cond-mat.soft

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cond-mat.soft 2026-05-13 1 theorem

Asymmetry tuning makes dielectric spheres interact as point charges at contact

Designing Coulombic Contact Interactions between Polarizable Particles through Asymmetry

Derived radius, charge, and permittivity ratios cancel polarization so many-body self-assembly matches pure Coulomb systems

abstract click to expand

Polarizable particle systems, including charged colloids, polarizable ions, biomolecular assemblies, and soft nanomaterials, can exhibit contact electrostatic interactions that depart strongly from Coulomb behavior when dielectric mismatch and geometric singularities amplify polarization effects. Here we use charged dielectric spheres as a model system and show that these polarization contributions can be canceled by jointly tuning size, charge, and dielectric asymmetries. By extending a recently developed image-charge formula to contacting dielectric spheres, we derive analytical conditions under which the contact interaction reduces to the bare Coulomb form. Accurate two-sphere calculations validate the resulting contact design rules with relative errors below $3\%$. Strikingly, many-body molecular dynamics simulations reveal that systems satisfying these two-body rules self-assemble into structures that closely match their pure Coulomb references. These results establish asymmetry as a route for turning electrostatic complexity into Coulombic simplicity at contact, with implications for controlled self-assembly and materials design.

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cond-mat.soft 2026-05-13 Recognition

Embryo junction wiggles follow inverse-square law

Fluctuation spectra of embryonic cell-cell interfaces reveal inverse-square scaling

Spatial and temporal spectra match tension-dominated membrane models even in actively reshaping tissue.

abstract click to expand

Tissue-scale shape changes are driven by ensembles of intracellular forces. However measuring force in these contexts remains a difficult challenge. Here we perform spectral analysis of transverse fluctuations of cell-cell junctions in \emph{Xenopus} embryonic tissue explants undergoing convergent extension. We developed an image analysis pipeline to extract fluctuation amplitude profiles $u(x,t)$ from time-lapse confocal movies and computed two-dimensional spatiotemporal power spectra. We observe power-law scaling of mean-squared fluctuation power spectra consistent with $\langle u_q^2 \rangle \sim q^{-2}$ and $\langle u_f^2 \rangle \sim f^{-2}$. The spatial scaling agrees with predictions from the Helfrich Hamiltonian, and the temporal scaling agrees with overdamped dynamics of a fluctuating membrane, both in the tension-dominated regime. Pharmacological reduction of actomyosin contractility (via low-dose blebbistatin or latrunculin B) did not significantly alter either scaling exponent. Our results provide an early empirical characterization of junction fluctuation spectra in an actively shape-changing tissue. Simple tension-dominated membrane models appear sufficient to describe transverse junction dynamics despite their active and coupled nature. This work establishes a quantitative baseline for future studies of tension-bearing tissues and motivates the development of physical models specific to multicellular systems.

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cond-mat.soft 2026-05-13 2 theorems

Onsager principle derives drop dynamics on uneven surfaces

Variational approach to droplet motion on uneven solid surfaces, including contact line dynamics and evaporation

Equations for contact-line motion and evaporation follow from free-energy variation in the overdamped limit

abstract click to expand

We show how dynamical equations for liquid films and drops on uneven surfaces, including contact line dynamics and evaporation/condensation effects, may be formulated as a variational dynamics, generated via Onsager's variational principle. The theory applies in the isothermal overdamped-dynamics limit. We apply this general approach to obtain several well-known results on contact line dynamics and to study drops pinning and sliding on inclined corrugated surfaces. This approach constructs the dynamical equations starting from the free energy of the system and therefore has the advantage that it naturally incorporates the correct equilibrium properties.

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cond-mat.soft 2026-05-13 1 theorem

Two-grain bridges supply 85% of capillary pressure in wet grains

Morphology-resolved stress contributions in sheared wet granular materials

Morphology tracking during shear shows complex clusters add little to cohesion, allowing parameter-free friction prediction

abstract click to expand

Three-dimensional X-ray microtomography, coupled to rheometric measurements, enables a morphology-resolved reconstruction of capillary stresses at the grain scale in unsaturated wet granular materials. Liquid domains are automatically classified into capillary bridges, dimers, trimers, and larger clusters, and their spatial organization is tracked as a function of shear deformation and liquid content. We show that shear localization governs the redistribution of the liquid phase: capillary bridges remain uniformly distributed throughout the sample, while higher-order morphologies accumulate preferentially near the lower boundary of the shear-zone through a shear-driven coalescence mechanism. Despite this spatial localization, simple two-grain bridges generate the dominant contribution to the isotropic capillary pressure, accounting for nearly 85\% of the total at liquid-to-solid volume ratio $\epsilon = 0.05$, whereas more complex liquid clusters contribute only weakly to the overall cohesion. Incorporating the morphology-resolved capillary pressure into an effective-stress framework qualitatively reproduces the macroscopic friction coefficient across the full range of investigated liquid contents, without adjustable parameters. These results establish a predictive micro--macro link between liquid morphology and the rheology of wet granular materials.

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cond-mat.soft 2026-05-13 Recognition

Flux limit at surface corrects diffusivity error in elastomers

Following the thread: surface and bulk solvent migration in silicone elastomers from local volumetric swelling

Local 3D volume tracking shows solvent entry is rate-limited at the interface, fixing an order-of-magnitude underestimate from bulk models.

abstract click to expand

Poroelastic materials, consisting of a permeable solid matrix infiltrated with fluid, are ubiquitous in natural and engineering contexts. In poroelastic polymer solids, the elastic matrix swells to equilibrium when immersed in a solvent bath; thus, the network elasticity couples to the solvent transport. Despite the ubiquity and importance of poroelastic theory in describing phenomena as diverse as earthquakes and biological tissues, there is a paucity of experimental data that probe the local network response to controlled stress and solvent boundary conditions. Here, we first probe the baseline diffusion kinetics of a polymeric solvent during free swelling of a polydimethylsiloxane (PDMS) network with well-characterized silicone oils. In situ 3D spatiotemporal measurements identify a flux-limited interfacial boundary condition, contradicting the canonical fully drained assumption. This correction eliminates an order-of-magnitude underestimation of diffusivity in standard bulk analysis. The swelling equilibrium is accurately captured by a Flory-Rehner theory that requires modification to include the effective finite extensibility of the filled network. Solvent migration is then studied using a bending configuration for three material preparations: as-prepared, mobile-phase-free, and fully swollen in silicone oils. The as-prepared and mobile-phase-free beams show no discernible volumetric change or force relaxation, whereas local in situ measurements directly resolve tensile-side dilation and compressive-side contraction, yielding the effective diffusivities in agreement with the force-relaxation data. These measurements rigorously benchmark solvent diffusivity in polymer networks, underscoring the importance of unambiguous interfacial boundary conditions and shedding light on mechanics and engineering across poroelastic polymers and geomaterials.

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cond-mat.soft 2026-05-13 2 theorems

Cell divisions suppress avalanches in tissue rearrangements

Cell divisions suppress dynamical correlations in solid tissues

They fluidize tissues below yield stress yet limit long-range correlated events through a finite energy budget, unlike passive solids.

abstract click to expand

Developing tissues often maintain mechanical coherence while continuously remodeling through cellular processes such as cell divisions and rearrangements. In this way, they are an example of amorphous solids. In passive amorphous solids, local rearrangements can trigger one another through long-ranged elastic interactions, leading to system-spanning avalanches near yielding. Whether similar collective dynamics should be expected in living tissues is unclear, because cell divisions generate stress and remodeling events independently of local mechanical stability. Here, we address this question using a two-dimensional elastoplastic model in which cell divisions are treated as active plastic events. We find that while cell divisions fluidize the tissue below the passive yield stress, but preserve the marginal stability in the quasistatic limit. However, they also strongly suppress the system-spanning avalanches of cell rearrangements, in constrast with the expected behavior in passive amorphous solids. Finally, we show that the avalanche supression originates from the energy balance in the system. Namely, the energy injected by cell divisions allows for shear flow below the yield stress, but also provides a finite budget for rearrangements. These results suggest that proliferating tissues display the structural hallmarks of marginal amorphous solids while exhibiting much shorter-ranged correlations in dynamics, compared to passive amorphous solids.

0

cond-mat.soft 2026-05-13 1 theorem

Hydrogel permeability collapses to master curve with PEGDA surface

Nanostructure of PEGDA-PEG hydrogel membranes and how it controls their permeability

Scaling as volume over surface reveals thin water films between facetted polymer domains control flow.

abstract click to expand

The spacial heterogeneity of hydrogels composed of PEGDA and added polymer chains is expected to play a crucial role on their transport properties which can be exploited in filtration or tissue engineering. However little is known about the arrangement of the polymer chains in the matrix and the length scales of these heterogeneities. Here we combine solid-state NMR and Small Angle Neutron Scattering to unravel the structure and dynamics of PEGDA hydrogels containing added PEG chains of various concentrations. Our results show that the samples present heterogeneities in both the PEGDA and PEG concentrations and suggest that the PEG chains entangle with the PEGDA network. When plotting the sample permeability, K, as a function the specific surface of the PEGDA heterogeneities we obtain a master curve, showing that the heterogeneity of the PEGDA matrix controls the permeability of the sample. Moreover the scaling K ___ V/S suggests a structure composed of facetted PEGDA/PEG heterogeneities separated by a network of aqueous thin and flattened films in which the water can permeate.

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cond-mat.soft 2026-05-13 2 theorems

Second hole alters wrinkle nucleation and spread in tensed sheets

Tensional wrinkling of thin elastic sheets with two circular holes

Bipolar stress analysis and floating-film experiments show hole separation sets threshold, sites, orientation and extent under tension.

abstract click to expand

A paradigm for the study of wrinkling in elastic sheet is the Lam\'{e} configuration, in which azimuthal wrinkles form in an annular sheet subjected to tensile loads at both edges. Since wrinkles are spatially extended, this instability provides a mechanism for stress transmission over long distances. A natural extension of this problem is wrinkling in sheets with multiple holes or broken symmetry. Here, we investigate tension-induced wrinkling in thin elastic sheets containing two circular holes by combining analytical modeling and experiments. The pre-buckled state is solved analytically using bipolar coordinates, enabling identification of the wrinkling threshold as a function of the distance between the two holes. Near-threshold wrinkling and interactions between wrinkles are analyzed, and we validate our theoretical predictions against experimental observations obtained through video imaging of spin-coated polystyrene sheets floating on liquid surfaces with controlled surface tension. Our results demonstrate that geometric symmetry breaking, such as the presence of a second hole, strongly influences wrinkle nucleation, orientation, and spatial extent. Beyond mechanics, these findings might provide a simple mechanism for cellular mechanosensing, where force transmission is amplified by mechanical instabilities.

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cond-mat.soft 2026-05-13 2 theorems

Acoustic force quantifies single-condensate viscoelasticity

Tracer-free Contactless Acoustic Microrheometry Quantifies Viscoelastic Spectrum of Phase-separated Condensates

Contactless measurements on microscale droplets yield shear-modulus spectra from 0.01 to 10 Hz, validated on dextran and applied to nucleic酸

abstract click to expand

The rheology of phase-separated condensates plays a central role in applications spanning advanced materials design and cellular processes, yet quantitative characterization of their viscoelasticity remains challenging due to the limitations of existing microrheological methods that require tracer particles or mechanical contact. Here, we establish tracer-free and contactless acoustic microrheometry as a versatile platform for quantifying the frequency-dependent complex shear modulus of single microscale condensates over 0.01-10 Hz. Using spatiotemporally controlled acoustic radiation force generated within a micro-acoustic resonator, this method deforms condensates for creep-recovery and oscillatory viscoelastic measurements. Quantitative validation using dextran condensates in a polyethylene-glycol continuous phase successfully captures their size- and frequency-dependent mechanical responses, while application to nucleic-acid condensates reveals salt-dependent internal viscoelastic changes at single-condensate resolution. By enabling quantitative dissection of condensate mechanics without invasive probes, acoustic microrheometry provides a broadly applicable framework for investigating phase-separated condensates across materials science, soft matter physics, biology, and beyond.

0

cond-mat.soft 2026-05-13 2 theorems

Minimal two-network model explains double-network toughness

Defect screening and load transfer in minimal hard-soft double networks

Load transfer screens defects in the hard network, producing universal failure-strain scaling and delocalized damage.

abstract click to expand

Double network (DN) materials exhibit anomalous strength and toughness that far exceed the sum of their constituents. While widely exploited, the fundamental physical mechanisms underlying this synergy remain elusive. Here, we show that a minimal three-dimensional model of two coupled, disordered linear-elastic networks is sufficient to capture the essential physics of DN nonlinear mechanics. The model reproduces the full suite of unique mechanical behaviors, including yielding, necking, strain hardening, and the brittle-to-ductile transition. Mechanical contrast between the hard and soft networks drives inter-network load transfer, which screens defects and suppresses stress concentrations in the hard network. By defining a stress-concentration factor, K_sc, we find that the hard-network failure strain scales universally as 1/K_sc, directly bridging microscopic defect screening to macroscopic yielding. We further show that complete defect screening triggers the shift from localized necking to delocalized damage. Furthermore, the stable necking plateau is identified as an energetic selection governed by the balance between potential energy release and irreversible dissipation. These findings reveal that a simple linear-elastic framework can account for the rich nonlinear landscape of DN materials, providing a general principle for designing next-generation tough solids.

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cond-mat.soft 2026-05-13 Recognition

Model separates soft elasticity from viscoelasticity in LCEs

Thermoviscoelasticity of polydomain liquid crystal elastomers regulated by soft elasticity

Rate-independent mesogen reorientation sets the limiting stretch while polymer relaxation adds rate dependence and residual buildup, all erc

abstract click to expand

Liquid crystal elastomers (LCEs) are elastomeric networks with rod-like mesogens that reorient under load. In polydomain LCEs, this reorientation drives a polydomain-to-monodomain transition that produces a soft-elastic plateau. Coupling between this soft elasticity and polymer-network viscoelasticity yields a path-dependent thermoviscoelastic response, central to applications in damping, impact protection, and tough adhesives. However, the physics governing this response under complex thermomechanical histories remains insufficiently studied. We present a combined experimental and theoretical study of polydomain LCEs under three uniaxial protocols: single-cycle loading-unloading, stress-free recovery from various pre-stretches, and multi-cycle loading with progressively increasing amplitude. We develop a finite-deformation constitutive model combining two parallel mechanisms: rate-independent, temperature-dependent soft elasticity from mesogen reorientation, and time- and temperature-dependent viscoelasticity. With a single parameter set, the model quantitatively reproduces all three protocols and resolves each mechanism's contribution. A temperature-dependent soft-elastic limit governs the low-rate response and the long-time recovered stretch, while viscoelasticity controls the rate-dependent deviation and the cycle-wise accumulation of residual stretch away from this limit. A thermal recovery test above the nematic-isotropic transition confirms that all hysteresis and residual deformation are reversible, ruling out irreversible damage. The framework provides mechanistic understanding and a predictive basis for designing polydomain LCE components under complex thermomechanical histories.

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cond-mat.soft 2026-05-13 Recognition

Polarization modulation is sinusoidal in one antiferroelectric nematic but soliton-like in

Landau theory applied to antiferroelectric ordering in ferroelectric nematic liquid crystals

In the antiferroelectric phase the polarization modulation is reasonably well approximated by a simple sinusoid in DIO, whereas in FNLC919…

abstract click to expand

The polarization and density modulation associated with antiferroelectric ordering is studied experimentally as a function of temperature in two ferroelectric nematic liquid crystals, the prototypical single compound (DIO) and a commercial mixture (FNLC919). The modulation wavenumber qA is determined by small angle X-ray diffraction from the weak smectic-like density wave (wavenumber qS = 2qA) that accompanies the polarization modulation. Results for qS and the saturated value of the polarization are analyzed in terms of Landau theory previously developed to describe the para-/antiferro-/feroelectric sequence of phase transitions in solid ferroelectrics. The analysis indicates that the polarization modulation is reasonably well approximated by a simple sinusoid in the antiferroelectric phase of DIO, whereas in FNLC919 the modulation develops a strongly soliton-like profile (with sharply decreasing wavenumber) close to the antiferro- to ferrolectric transition.

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cond-mat.soft 2026-05-12 2 theorems

Active stresses broaden pores and thicken bundles in actin networks

Mechanics of heterogeneous fiber networks

Raising motor concentration increases local elastic modulus and lengthens the range of strain propagation at network heterogeneity scales.

abstract click to expand

Internally generated active stresses drive soft materials into architectures inaccessible to thermal self-assembly. We use a microtubule-based active fluid to assemble and irreversibly restructure actin-fascin networks. Subsequently, we probe the mesoscale mechanics of such networks by combining active microrheology with fluorescence imaging of the strain field around the probe. Increasing motor concentration broadens the pore-size distribution and thickens load-bearing bundles, raising the mean local elastic modulus and its spatial variability. Displacement fields of actively-processed networks propagate over longer range when compared to unprocessed networks. At large strains, both networks strain soften and plastically restructure. The combined microrheology and strain-imaging approach show that tunable active stresses reprogram the structure and viscoelastic response of fiber networks at the scale of their structural heterogeneity.

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cond-mat.soft 2026-05-12 Recognition

Partially wet states limited to specific contact angles and curvatures

Existent condition of partially wet state in capillary tubes

Energy minimization shows corner films exist only in a bounded region of parameter space for square tubes.

abstract click to expand

We develop a theory that predicts the equilibrium states of a fluid contained in a capillary which has corners. Each section of the tube can take three states: completely wet state where the tube section is completely occupied by the fluid, partially wet state where only the corners are occupied by the fluid known as corner film or finger, and completely dry state. We calculate the phase diagram of these states for a square tube with rounded corners. It is shown that the partially wet state can exist only in a certain region in the parameter space spanned by the equilibrium contact angle and the corner curvature.

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cond-mat.soft 2026-05-12 2 theorems

High-concentration lithium electrolytes couple coordination to mesoscale clusters

A molecular perspective on coordination, screening, and emergent length scales in lithium electrolytes

Screening and transport emerge together from correlated ion structures, requiring simultaneous control over all length scales.

abstract click to expand

Lithium electrolytes are commonly described using separate conceptual frameworks for local coordination chemistry, electrostatic screening, and ionic transport. This separation is effective in dilute conditions but breaks down at higher concentration, where coordination, ion pairing, clustering, and collective dynamics become intrinsically coupled. In this Perspective, we develop a unified multiscale framework that links local coordination motifs, mesoscopic ionic organization, and macroscopic transport within a single physical picture. Through representative examples spanning carbonate liquids, polymer electrolytes, concentrated systems, and confinement, we show that increasing concentration drives a systematic evolution from solvent-dominated Li$^+$ coordination to ion pairing, clustering, and correlated domains. In this regime, screening and transport are not independent phenomena but arise from the same underlying correlated structures. This perspective implies that rational electrolyte design must simultaneously control short-range coordination, mesoscale organization, and collective electrostatic response.

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cond-mat.soft 2026-05-11 2 theorems

Knot topology drives reentrant conformations in copolymer rings

On the thermal properties of knotted block copolymer rings

Small changes in attractive block length trigger nonmonotonic temperature responses and knot localization shifts.

abstract click to expand

We investigate the thermal and structural properties of knotted diblock copolymer rings using a coarse-grained lattice model in an implicit solvent. The system is studied by means of the Wang--Landau Monte Carlo algorithm, allowing us to analyze thermodynamic and conformational responses over a wide temperature range. Different knot topologies, including the unknot, trefoil, figure-eight, and pentafoil knots, are considered for both symmetric and asymmetric monomer compositions. In the AB model employed here, A-type monomers are self-repulsive, B-type monomers are self-attractive, and A-B interactions are neutral, such that the solvent is effectively good for A-type monomers and poor for B-type monomers at low temperatures. We analyze several key observables, including the heat capacity, the radius of gyration, and its temperature derivative for both the entire copolymer ring and the individual blocks, and the probability that a monomer belongs to the knotted region. Our results show that the interplay between knot topology, monomer composition, and temperature strongly influences polymer conformations. Small variations in the B-block length induce nonmonotonic, reentrant-like conformational behavior as a function of temperature, including transitions between knot localization and delocalization at low temperatures. These effects arise from the competition between energetic and entropic contributions imposed by topological constraints.

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cond-mat.soft 2026-05-11 2 theorems

Like-charged particles attract via solvent polarization in liquids

Interparticle Interactions in Nonlocal Media: Attraction and Repulsion from Charge-Polarization Coupling

Nonlocal dielectric model shows charge and polarization balance produces attractions, repulsions, and mobility absent from classical theory.

abstract click to expand

Recent measurements of microsphere interactions in diverse media suggest that the standard dielectric-continuum models of solution-phase interactions are fundamentally incomplete. Experiments indicate that the interactions of charged particles in liquids can be dominated by solvent structuring at interfaces, thereby motivating the concept of electrosolvation. While interfacial spectroscopy and molecular simulations have established that solvent molecules can exhibit net orientation at interfaces, conventional theoretical frameworks treat the fluid as a structureless medium described by a constant dielectric permittivity. This view does not envisage a contribution of interfacial polarization to interactions at longer range. Here, we employ nonlocal dielectric theory accounting for spatial correlations in polarization to describe interactions in solution. This model permits both charge and polarization to govern interactions, leading to dramatic departures from classical expectations. Specifically, the balance between charge and polarization generates a framework of symmetric (repulsive) and antisymmetric (attractive) interactions, wherein: (i) like-charged surfaces can attract at long range, (ii) oppositely charged objects can repel, and (iii) neutral matter can acquire effective electrical mobility and display long-range forces-potentially explaining long-range hydrophobic attraction. Further, like-charged biomolecules can attract in aqueous electrolytes even for modest polarization correlation lengths ($\xi=2$ \AA). Our results also suggest that electrosolvation effects may underpin flocculation in suspended matter, which has traditionally been attributed to attractive dispersion forces. These findings indicate how solvent structuring and correlations may play a dominant, complex role in fluid-phase physics.

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cond-mat.soft 2026-05-11 Recognition

Perpendicular orienting field lowers activity threshold in active nematics

Orienting-Field Effects on Instability and Mode Selection in Active Nematics

It also enables a new even-symmetry instability while parallel alignment raises thresholds and stabilises the system.

abstract click to expand

We examine the instabilities of a confined active nematic subjected to an orienting field using a low Reynolds number Ericksen-Leslie framework with active stresses and field-induced torques. Linear analysis reveals two distinct modes, with odd and even director symmetry, the instabilities of which depend on the interplay between activity and field strength. We derive exact and approximate analytic forms of the stability boundaries and show that an orienting field that aligns the director perpendicular to the substrate anchoring direction cooperatively lowers activity thresholds and enables a field-driven even symmetry mode instability, while an orienting field that aligns the director parallel to the substrate anchoring tends to stabilise the system. Numerical solutions of the full nonlinear equations show that the linear stability analysis correctly identifies the symmetries of long-time states. These results demonstrate how orienting fields can promote an instability below the classical critical activity and can be used to both tune the instability onset and control the mode selection in confined active nematics.

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cond-mat.soft 2026-05-11 2 theorems

Custom asperity shapes program nonlinear friction laws

Inverse Design of Metainterfaces for Static Friction Control: Beyond the Hertzian Limit

Differentiable contact model finds topographies matching target behaviors using few elements per unit cell

abstract click to expand

Programming the static friction of mechanical interfaces is critical for soft robotics, haptics, and precision gripping. Static friction is governed by the real contact area, and standard rough surfaces exhibit a linear area-load scaling inherent to classical Archard and Greenwood-Williamson models, severely restricting their functional range. Here, we propose a framework for the inverse design of tribological metainterfaces engineered for programmable contact behaviors. By utilizing general axisymmetric asperities, we unlock nonlinear macroscopic responses unattainable by standard Hertzian contacts. To solve the inverse problem, we embed a fully differentiable contact mechanics engine within a neural network and a quadratic optimizer. We leverage regularized physical gradients to automatically discover non-standard topographies that reproduce complex target friction laws, with only a few asperities in unit cells. The predicted designs are strictly validated against high-fidelity Boundary Element Method (BEM) simulations. This framework bridges data-driven optimization and rigorous physics, offering a scale-invariant pathway for discovering functional tribological surfaces.

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cond-mat.soft 2026-05-11 1 theorem

Nano-clay emulsions cut steel friction by 84 percent

Nano-Clay-Stabilized Water-in-Oil Colloidal Pickering Emulsions as Thixotropic Lubricant

Thixotropic water-in-oil Pickering emulsions outperform oil and water via adaptive interfacial films under high pressure.

abstract click to expand

The limitations of conventional mineral oil-based lubricants motivate the development of environmentally benign emulsions capable of providing lubrication and heat dissipation in demanding applications. In this study, nano-organoclay (Garamite 1958)-stabilized thixotropic water-in-oil Pickering emulsions are developed using sunflower oil as the base. The rheological and tribological properties of the emulsion system are systematically examined. Rheological findings reveal a pronounced increase in yield stress, shear thinning and thixotropic behavior on increasing Garamite loading percentage in the emulsion. The tribological performance is assessed against dry, water, and oil-lubricated conditions for a steel-steel interface under high contact pressure. The findings indicate that the tribological performance is significantly influenced by the microstructure and thixotropic behavior of the emulsions. The emulsion with the optimal nano-clay concentration demonstrates approximately 41\% and 84\% lower friction and approximately 80\% and 96\% lower wear than oil and water, respectively. The emulsion exhibits sensitivity to the sliding direction and displays load-responsive friction behavior with a memory effect owing to the reversible structuring of the clay-droplet network. This superior performance is attributed to the combined effects of thixotropy, anisotropic nanoclay morphology, and stable droplet armoring, which form a robust and adaptive interfacial film. This study advances the understanding of Pickering emulsions in metallic tribosystems by correlating the microstructure and rheology with tribological performance, thereby facilitating the design of high-performance, smart, and eco-conscious lubricants for metallic systems.

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cond-mat.soft 2026-05-11 Recognition

Zero modes in soft plates follow damped pendulum dynamics

Dynamical geometric modes in non-Euclidean plates

Periodic driving excites oscillations and rotations in the softest mode even after aging selects a preferred shape.

abstract click to expand

When subjected to specific prestresses, continuum elastic shells can exhibit geometric zero modes: complex motions that require vanishing elastic energy to excite, enabling them to be driven by weak and generic energy inputs. Despite recent interest in these modes, we understand very little about their dynamical properties. Non-Euclidean plates modeled on minimal surfaces are one example in which prestresses and geometry combine to produce a continuum of ground states that the plate can explore through a geometric zero mode. We demonstrate that a non-Euclidean plate with metric corresponding to Enneper's minimal surface exhibits the predicted continuous stability, but this degeneracy is ultimately lifted by aging. Despite developing a preferred configuration, the zero mode remains the softest mode. Using a combination of analytical theory and experiments, we show that the elastodynamics of this soft mode is captured by the dynamics of a damped pendulum. A periodic driving uncovers resonance phenomena in this pendulum mode, such as small oscillations and steady rotations, but mixes with an additional flapping mode at high frequencies.

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cond-mat.soft 2026-05-11 1 theorem

Yield-stress bath expands frontal polymerization to low-viscosity polymer inks

Embedded Direct Ink Writing of Thermoset and Elastomeric Polymers via Frontal Polymerization

Embedded printing decouples shape retention from chemistry, enabling smaller features and complex interlinked thermoset architectures.

abstract click to expand

Direct ink writing (DIW) using frontal ring-opening metathesis polymerization (FROMP) offers a compelling route to the rapid and energy-efficient fabrication of thermoset and elastomeric polymer architectures, leveraging a self-propagating exothermic curing reaction. While FP-DIW excels at freestanding path printing due to the rapid solidification, it is constrained by stringent rheological requirements, a lower bound on achievable feature size due to quenching, and the need for the reaction front to closely follow the nozzle during printing. Here, we overcome these constraints by leveraging embedded 3D printing to implement FP-DIW with delayed solidification, thereby decoupling shape retention and solidification from ink chemistry and rheology. The use of a yield-stress support medium enables extrusion of low-viscosity inks by suppressing gravitational and capillary instabilities, mitigating front quenching at small diameters, and allowing time-delayed solidification to fuse complex, overlapping, and mechanically interlinked features after deposition. Two complementary thermal initiation strategies are introduced:\ volumetric dielectric heating via microwaves and surface heating at the boundary of the support bath. Formulations based on dicyclopentadiene (DCPD), cyclooctadiene (COD), and mixtures thereof, result in tunable final mechanical properties with glass transition temperatures spanning $-50$ to $160 $$^\text{o}$C. The versatility of this approach is demonstrated through the fabrication of lattices, springs, mechanically interlocked, and multimaterial architectures. Compared to printing in air, this embedded approach introduces a substantially broader range of possible formulations, material properties, feature sizes, and architectures.

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cond-mat.soft 2026-05-11 2 theorems

Lubrication layer makes non-Newtonian flow Newtonian

Lubrication-Induced Newtonianization Enables Passive Transport of Non-Newtonian materials

Shear confined to a thin low-viscosity boundary lets geometry and lubricant set the transport rate, slashing required driving forces for a

abstract click to expand

Non Newtonian flows are typically governed by intrinsic bulk rheology, which imposes strong constraints on transport through confined geometries. Here, we show that stable boundary lubrication can fundamentally alter this behavior by localizing shear within a thin, low-viscosity interfacial layer. As a result, the nonlinear rheological response of a broad class of complex materials, including yield-stress, shear-dependent, and thixotropic materials, is strongly suppressed during flow. Using analytical solutions of Stokes flow and numerical simulations, we demonstrate that lubrication-induced shear localization leads to an apparent Newtonianization of transport, in which the macroscopic flow response becomes primarily controlled by the lubricating layer and geometric confinement rather than the intrinsic material properties. In this regime, materials that would otherwise require large pressure gradients can be transported at substantially lower driving forces. Notably, this boundary-dominated transport enables gravity-driven passive flow with orders-of-magnitude enhancement in throughput compared to rigid-wall conduits. These results establish lubrication as a powerful mechanism for tuning and simplifying complex fluid transport, with implications for biological systems, soft and jammed materials, and energy-efficient fluids.

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cond-mat.soft 2026-05-11 2 theorems

Insertion depth drives concentration-dependent bilayer destabilization

Concentration-Dependent Membrane Destabilization in DPPC Bilayers: Distinct Insertion Mechanisms and Stress Redistribution by Chloroform and Alkanols

Simulations show chloroform thins membranes while alkanols crowd interfaces and redistribute stress without full melting.

abstract click to expand

How do solute concentration and molecular chemistry govern the transition from membrane saturation to destabilization? We address this using microsecond-scale molecular dynamics simulations of dipalmitoylphosphatidylcholine (DPPC) bilayers with chloroform (CHCl$_3$) and a homologous series of alkanols (methanol, ethanol, octanol) over $0-50\%$ concentrations. Although complete membrane melting is not observed within $1000\, ns$, all systems exhibit clear precursors of destabilization, including enhanced thickness fluctuations, reduced lipid order, and mechanical softening. Chloroform induces pronounced thinning and large fluctuations, consistent with deep, transient insertion. Methanol perturbs primarily the headgroup region, while ethanol shows intermediate behavior with partial insertion. Octanol preserves bilayer thickness at high concentrations due to lipid-like insertion but significantly increases fluctuations and interdigitation. Across all systems, increasing concentration decreases the area compressibility modulus and deuterium order parameter, accompanied by smoothing of lateral pressure profiles, indicating stress redistribution. Free energy analysis reveals increased membrane partitioning and reduced translocation barriers with concentration, strongest for octanol and weakest for methanol. These results demonstrate that membrane destabilization is governed by the interplay of insertion depth, interfacial crowding, and lipid packing disruption.

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cond-mat.soft 2026-05-11 2 theorems

Model predicts wrinkling and crumpling of evaporating droplets at oil-air boundary

Elastocapillary morphing of self-encapsulated droplets floating at the oil-air interface

Energy minimization with a tension-relaxation rule produces phase diagrams controlled by Bond number, surface-tension ratio and density.

abstract click to expand

Self-encapsulated droplets floating at an oil--air interface undergo striking shape changes during evaporation, including flattening and localized loss of membrane tension leading to crumpling and wrinkling. Here we combine experiments, modeling and simulations to obtain predictive morphological maps. We perform contact-angle and evaporation experiments on water droplets coated by a hydrophobin protein film and floating in a fluorinated oil, providing reference profiles and volume-loss sequences for quantitative validation. We develop an axisymmetric mechanics framework in which equilibria follow from minimization of a total free energy combining surface energies, membrane strain energy and gravitational potential, subject to volume and contact-line constraints. A quasi-convex tension-relaxation rule accounts for compression-free states and enables coexistence of taut, wrinkled (one principal tension vanishes) and crumpled (both vanish) membrane domains. A finite element algorithm computes quasi-static morphing under volume reduction; key parameters are identified by fitting the reference contact-angle profile and then used without further tuning. The model reproduces the experimentally observed shape evolution and resolves the associated stress redistribution. Systematic parameter scans yield morphological phase diagrams governed by the Bond number, the oil--droplet surface-tension ratio and the density ratio. For buoyant droplets, crumpling relocates between exposed and submerged caps as parameters vary; for heavy droplets, a crossover to circumferential wrinkling along the immersed sidewall emerges. Wall-meniscus variations shift phase boundaries and can suppress bottom crumpling, consistent with wall-affected experiments.

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cond-mat.soft 2026-05-11 Recognition

Odd viscosity leaves droplet deformation unchanged at leading order

Droplet Deformation and Emulsion Rheology in Two-Dimensional Odd Stokes Flow

Analytical solution shows Taylor parameter equals capillary number to first order while higher-order effects and emulsion viscosities depend

abstract click to expand

We study the deformation of a two-dimensional viscous droplet in simple shear in the presence of odd viscosity. We derive an analytical solution for the droplet shape and surrounding flow field within the framework of odd Stokes flow, allowing for differences in both even and odd viscosity between the droplet and the surrounding fluid. This solution yields closed-form expressions for the macroscopic apparent even and odd viscosities of a dilute emulsion. We show that, provided all viscosity differences remain moderate, the steady-state Taylor deformation parameter satisfies $D_T^\infty = \text{Ca} + \mathcal{O}(\text{Ca}^2)$ so that the leading-order droplet deformation is unchanged from the classical (even-viscous) result. Nevertheless, pronounced effects emerges beyond leading order, where our direct numerical simulations reveal odd-viscous differences to the droplet deformation. In addition, we show that the flow is influenced only by the difference in odd viscosity between the droplet and the medium and not on their individual values. Our analysis clarifies how odd viscosity might modify the effective rheology of dilute emulsions and provides a framework for interpreting droplet-based measurements of odd-viscous response. Key words: odd viscosity $|$ droplets $|$ emulsions $|$ surface tension $|$ chiral fluids

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cond-mat.soft 2026-05-08

Weighted dissipative stress restores local rheology in dense flows

Non-Local Particle Flows Become Local When Considering Dissipative Stress

Redefining stress as shear-rate average of irreversible work makes μ(J) hold throughout the bulk of inhomogeneous suspensions

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Dense granular and suspension flows under inhomogeneous shear exhibit persistent particle motion in regions where the local yield criterion is subcritical, an apparent breakdown of locality that has motivated the development of a generation of nonlocal rheological models. Using particle-resolved simulations of frictionless dense suspensions in two-dimensional Kolmogorov flow, we show that two independent considerations together account for this signature. First, replacing the conventional shear stress by a shear-rate-weighted dissipative stress $\tau_W=\langle \tau \dot \gamma \rangle/\langle \dot \gamma \rangle$, which isolates the component of stress that performs irreversible work, restores the homogeneous $\mu(J)$ law throughout the bulk of the flow, with the inferred friction remaining strictly above yield. Second, a simple geometric mixing-length construction, applied with conventional stresses and requiring no fluctuation input, accounts for the residual sub-yielding within a sub-diameter layer at flow reversals. Each approach is based on a different philosophy and mechanism, and together they suggest that much of the apparent non-locality in this geometry and frictionless case is an artefact of how stress is measured and averaged rather than an intrinsic breakdown of local rheology.

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cond-mat.soft 2026-05-08

Cooking time tunes fudge from ductile to brittle

Cooking crystalline candies and the ductile to brittle transition in concentrated suspensions

The same progression appears in calcite suspensions as crystal volume fraction rises from jamming toward close packing.

abstract click to expand

The existence and origin of the ductile to brittle transition in non-Brownian suspensions and pastes is underexplored despite the ubiquity of such materials in practical applications. We demonstrate the phenomenon in candies of sugar crystals in a water-protein-fat matrix prepared by boiling a sugar-cream-butter mixture (known as 'fudge' in some countries). As cooking time or final cooking temperature increases, we observe a transition from a fluid to a ductile solid, then to a brittle solid that abruptly fractures in compression. We propose that this is driven by rising solid sugar crystal volume fraction, and indeed find the same sequence of behaviour in a suspension of non-Brownian calcite particles as the solid fraction moves from frictional jamming to random close packing. Particle-based simulations reveal the sensitivity of the observed phenomenon to boundary conditions.

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cond-mat.soft 2026-05-08

Solvent memory produces two-step ionic relaxation

Solvent-induced memory effects in a model electrolyte

Modeling ions and solvent as Brownian particles yields explicit charge-fluctuation formulas for fast solvents and predicts an extra slow-rel

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The fluctuations of ions in polar solvents remain poorly understood theoretically due to the complex coupling between ionic motion and solvent polarization. Indeed, while all-atom resolution can be achieved in numerical simulations, analytical approaches require suitable levels of coarse-graining. In this work, we describe ions and solvent molecules as interacting Brownian particles and use stochastic density functional theory to derive a generalized Langevin equation for the ionic charge density, explicitly accounting for solvent-mediated memory effects. In the regime where there is a clear timescale separation between fast solvent and slow ion dynamics, we obtain simple expressions for dynamical charge structure factors, which are validated by BD simulations. For slow solvents, we predict an emerging two-step relaxation in ionic dynamics. These results provide a mesoscopic approach for ion-solvent dynamics and open pathways to study fluctuation-induced phenomena in electrolytes.

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cond-mat.soft 2026-05-07 2 theorems

Three tests determine fracture behavior of any cementitious structure

A Guide to Fully Characterize the Fracture Properties of Cementitious Materials from Simple Experiments

Cylinder compression, Brazilian splitting, and wedge splitting extract the elasticity, strength surface, and toughness that predict crack on

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Guided by recent advances in the understanding of nucleation and propagation of fracture in elastic brittle materials, this paper proposes a suite of three simple experiments that permit the measurement of the three macroscopic material properties governing when and where cracks nucleate and propagate in structures made of cementitious materials that are subjected to arbitrary monotonic quasi-static loading conditions. The first experiment is that of the uniaxial compression of a cylindrical specimen, which enables the extraction of the elastic properties -- namely, the Young's modulus and Poisson's ratio -- as well as the uniaxial compressive strength. The second experiment is the Brazilian fracture test, performed with flat platens on a material disk to determine the uniaxial tensile strength. Having knowledge of the uniaxial compressive and uniaxial tensile strengths then allows for the estimation of the strength surface of the material via interpolation (e.g., a Drucker-Prager fit). Finally, the third experiment is the wedge split test on a notched cube, which yields the fracture toughness. We demonstrate by means of direct comparisons with four-point and three-point bending tests on both unnotched and notched beams made of a 3D-printable mortar mixture that the elasticity, strength, and toughness properties obtained from the proposed tests are sufficient to predict the nucleation and propagation of fracture for any structure (granted separation of length scales) made of cementitious materials under any monotonic quasi-static loading condition.

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cond-mat.soft 2026-05-07

Defects break chiral order in nonreciprocal flocks

Breakdown of Emergent Chiral Order and Defect Chaos in Nonreciprocal Flocks

Rotating states collapse into chaotic patterns with finite correlation length that diverges when nonreciprocity vanishes.

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We show that chiral order in two-dimensional nonreciprocal flocking mixtures is generically unstable. Combining large-scale agent-based simulations with a coarse-grained continuum description, we demonstrate that rotating chiral states emerging from antisymmetric couplings are destroyed by the proliferation of topological defects. The resulting dynamics is spatiotemporally chaotic and characterized by a finite correlation length that diverges as nonreciprocity vanishes. On length scales below this cutoff, density and orientational order fluctuations remain scale-free, but the associated scaling exhibits nonuniversal exponents. We attribute this atypical behavior to the coupling between density and order, which causes topological defects to act as persistent sources of nonlinear fluctuations.

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cond-mat.soft 2026-05-07

Disorder lengthscale drives nonlinear phonon dispersion in solids

Nonlinear phonon dispersion in disordered solids and non-Debye vibrational spectra

The same scale sets wave attenuation; both it and non-phononic modes shape the boson peak depending on disorder strength.

abstract click to expand

All solids, whether crystalline or disordered, support elastic wave propagation with a linear dispersion relation in the long-wavelength limit. These waves, corresponding to low-frequency phonons, feature a vibrational density of states that follows Debye's classical model. Deviations from Debye's predictions with increasing frequency can emerge from phonon dispersion nonlinearity and from non-phononic vibrational modes, which exist in non-crystalline solids due to structural disorder. Both nonlinear phonon dispersion in disordered solids and its relative contribution to non-Debye anomalies, most notably manifested by the controversial boson peak, remain poorly understood. Here we show that nonlinear phonon dispersion in a broad range of disordered solids, including elastic networks and various glasses, emerge from a mesoscopic, disorder-induced lengthscale, which also controls wave attenuation. We subsequently use analysis and large-scale computer simulations to quantitatively determine the relative contributions of nonlinear phonon softening and non-phononic vibrations to the onset of non-Debye anomalies and to the boson peak. We show that the relative magnitude of the two contributions strongly depends on the strength of disorder of the solid, e.g., controlled by the thermal history upon glass formation, and that for realistic laboratory glasses both pieces of physics significantly contribute to the boson peak. These findings constitute basic progress in understanding disordered solids.

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cond-mat.soft 2026-05-07

Colloidal glasses act like homogeneous materials at particle diameters

Local elastic perturbation of colloidal suspensions near the colloidal glass transition

Oscillatory motion decays as 1/r from the probe and moduli match bulk rheology, showing macroscopic descriptions hold at microscopic lengths

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Isolated microscopic magnetic particles are used to induce local perturbations in dense colloidal suspensions by rotating an external magnet. Confocal microscopy enables tracking of both the magnetic probe particle and adjacent colloidal particles. A probe particle moves with a circular trajectory. Knowing the external force and measuring the amplitude and phase of the probe motion allows us to infer the storage and loss moduli of colloidal suspensions at various volume fractions. These measurements are in qualitative agreement with previous results from conventional rheology. To further analyze the system's response, the oscillatory amplitude of colloidal particles is evaluated as a function of distance from the probe, revealing a 1/r decay in amplitude, consistent with a homogeneous viscoelastic material. These observations confirm that continuum descriptions of the colloidal samples are effective down to length scales comparable to the particle diameter.

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cond-mat.soft 2026-05-07

Friction shapes colloidal clusters more than its strength suggests

Understanding the Dynamics of Evaporation-Driven Colloidal Self-Assembly

Simulations show that varying interparticle friction switches evaporating particles between open, closed, and compact clusters across wide,

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Complex colloidal cluster morphologies are desirable for the fabrication of advanced materials, such as photonic crystals and meta-materials, and can be formed through evaporation-driven packing. By coupling lattice Boltzmann and discrete element methods, here we elucidate the rich interplay between fluid and particle dynamics during evaporation-driven self-assembly of spherical colloidal particles. We construct a regime diagram for a wide range of evaporation rates, interparticle friction coefficients, and particle numbers, identifying parameter regimes for open, closed, and minimal moment of inertia cluster configurations. Analyzing the competition between capillary, hydrodynamic, normal, and friction forces, we show that interparticle friction can exert a disproportionately strong influence on the final packing outcome despite being considerably smaller in magnitude than other forces at play. Our simulation results further highlight the potential for tuning colloidal cluster configurations via their dynamic trajectories.

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cond-mat.soft 2026-05-07

Model sets polymer brittle-ductile transition to inverse of beta-relaxation time

Predicting the Brittle-to-Ductile Transition in Amorphous Polymers

Upper strain-rate bound for uniform flow in the SL-TS2 description reproduces measured transitions in polystyrene, PMMA and PVC.

abstract click to expand

Brittle-ductile transition (BDT) is an important characteristic of amorphous (and semicrystalline) polymers. For a given strain rate, at temperatures above BDT, the polymers exhibit strain softening followed by yield and strain hardening, while at temperatures below BDT, the same materials exhibit brittle failure at relatively low strains. Surprisingly, today there is no simple model describing BDT as a function of polymer chemistry, sample history, deformation type, and strain rate. Experimental data suggest that BDT is often, though not always, associated with the beta-transition. We formulate a simple scalar model to describe the visco-elasto-plastic shear stress-strain curves as functions of temperature and strain rate. We also show that within this model, there is always an upper bound on the strain rate where the material can have a uniform viscoplastic flow; this upper bound is taken to represent the BDT. We stipulate that this upper bound is inversely proportional to the Johari-Goldstein beta-relaxation time. Using our "general" Sanchez-Lacombe "two-state, two-(time)scale" (SL-TS2) model, we compute the BDT for three polymers (polystyrene, poly(methylmethacrylate), and poly(vinylchloride)) and found a good agreement with experimental data.

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cond-mat.soft 2026-05-07

Condensin reverses DNA loops via catch-bond intermediate

Loop Extrusion Reversal by Condensin Motor is Mediated by Catch Bonds

Postulated ATP-cycle state shows lifetime that rises then falls with force, explaining observed backward steps.

abstract click to expand

Structural Maintenance Complexes (SMC) are energy consuming motors that are important in folding the genome by loop extrusion (LE) in all stages of the cell cycle. Single molecule magnetic tweezer pulling experiments have revealed that condensin, a member of the SMC family involved in mitosis, takes occasional backward steps, thus coughing up the gains in the length of the extruded loop. To reveal the mechanism of the forward and backward steps simultaneously, we developed a theory using the stochastic kinetic model and the scrunching mechanism for LE. The calculations quantitatively account for the measured force-dependent step size and dwell time distributions in both the directions. By postulating the existence of an intermediate state in the ATP-driven cycle that is poised to take a forward or a backward step, we predict that its lifetime increases as the external mechanical force increases till a critical value and subsequently decreases at higher forces. The surprising finding of lifetime increase in an active motor, at sub-piconewton forces, is the characteristic of catch bonds, known in force-induced rupture of several passive protein complexes. The identification of catch bond-like states in condensin not only expands our understanding of LE but also highlights the significance of mechanical forces in regulating genome organization.

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cond-mat.soft 2026-05-07

Attraction boosts colloid spreading in porous media

Diffusiophoretic dispersion of a colloidal blob in porous media

Experiments show the opposite of intuition because particles swap between fast and slow flow paths under diffusiophoresis.

abstract click to expand

Predicting and controlling the transport of colloids in porous media is essential for applications ranging from contaminant remediation to drug delivery. In these complex environments, solute gradients are ubiquitous and could drive diffusiophoretic particle migration, yet their impact on macroscopic colloid dispersion remains poorly understood. Here we combine experiments and simulations to quantify how diffusiophoresis alters the spreading of a colloidal blob in a 2D ordered/disordered porous medium. A joint blob of colloids and salt at high concentration is introduced into a medium filled with salt at low concentration and advected by a background flow. Intuition suggests that when colloids are attracted toward or repelled from the solute-rich blob, dispersion should be suppressed or enhanced, respectively. Instead, we observe the opposite trend: longitudinal dispersion is enhanced in the attractive case, whereas dispersion is suppressed in the repulsive case. Numerical simulations reveal that this striking reversal arises from diffusiophoretic exchange of particles between slow and fast streamlines, which we capture using a minimal two-layer model of coupled fast and slow plug flows. Finally, we probe how geometric disorder in the medium modulates this mechanism. Our results demonstrate that diffusiophoresis can strongly modulate macroscopic dispersion of colloids in porous media with implications for transport in subsurface and biological environments.

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cond-mat.soft 2026-05-06

Rotating drives switch binary particles between stripes and jams

Pattern Formation and Stick-Slip Dynamics in Binary Particle Assemblies with Rotating Drives

Frequency changes trigger lane patterns with abrupt transport jumps at low rates and restore small-orbit ordering at high rates in repulsive

abstract click to expand

We numerically examine a binary system of particles with repulsive interactions, where one species is driven by a rotating drive and the other is subjected either to a constant drive in a fixed direction or to a rotating drive that is out of phase with the first species. As a function of rotation frequency, we find a variety of order-disorder transitions and pattern forming states, including density-modulated stripes, partially jammed states, phase separated fluids, and mixed fluids. When one species has a constant drive and the drive on the other species is rotated at low frequencies, the system switches between different pattern forming phase-separated lanes including density-modulated stripes and partially jammed states, similar to what is observed for oppositely driven colloids. The lanes tend to align with the net direction of rotation, resulting in a series of order-disorder switching transitions. The transport curves show abrupt jumps up or down at the transitions, which also correspond with changes in the topological order. We find similar switching transitions when both species rotate out of phase with each other. For intermediate driving frequencies, the system becomes increasingly fluid-like and the laning behavior is lost. At high frequencies, however, the system can again exhibit patterned flow when the rotation orbits become smaller than the average spacing between particles. The switching is reduced when a finite temperature is included, but even for temperatures at which the uniform equilibrium bulk system is liquid, the partially jammed state can generate local density enhancements that lead to recrystallization. We demonstrate the pattern switching behavior for systems with different screened repulsive interaction potentials.

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cond-mat.soft 2026-05-06

Hydrophobic surfaces mix wall friction with flow drag for adsorbed polymers

Macromolecular tribology at flowing solid/liquid interfaces

Single-molecule tracking shows chains rubbing the solid while being dragged by near-surface flow, with broad friction coefficients from slow

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Molecular-scale interactions between solvated macromolecules and solid surfaces govern a large number of processes, from biology to engineering. Yet, despite extensive characterization at the macroscopic level, our molecular understanding of polymer/surface interactions remains limited, particularly under out-of-equilibrium conditions. Here, we combine wide-field single-molecule microscopy with microfluidic transport to directly track the nanoscale dynamics of individual fluorescently tagged macromolecular PEG adsorbates, and investigate their subtle couplings with interfacial hydrodynamic flows. At equilibrium, we evidence marked surface dependence, with macromolecular dynamics switching from heterogeneous non-Brownian diffusion on hydrophilic glass to bidimensional Brownian-like transport in an interfacial physisorbed state on hydrophobic self-assembled monolayers. While for hydrophilic glass, the effect of the flow is restricted to an advective contribution during solvent-mediated flights, we uncover for the hydrophobic surfaces a peculiar regime of mixed macromolecular friction, whereby the adsorbed chain rubs on the solid wall while being continuously dragged by the near-surface hydrodynamic flow through interfacial slippage. Through joint analysis of equilibrium and out-of-equilibrium transport, we finely disentangle these molecular level frictional interactions with both the solid surface and the interfacial liquid. Beyond population-averaged dynamics, we further unveil a broad distribution of friction coefficients associated to individual chains, which we attribute conformational heterogeneities with sluggish reorganization timescale. By enabling direct observations of molecular-scale interfacial dynamics, our approach provides a novel molecular picture of macromolecular friction and adsorbate/surface interactions at flowing solid/liquid interfaces.

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cond-mat.soft 2026-05-06

Standard simulations produce hard-sphere fluid-crystal coexistence

Comment on "The elusive fluid-and-crystal coexistence state in simulations of monodisperse, hard-sphere colloids"

A comment shows metastable fluid nucleating spontaneously into coexistence using ordinary methods, addressing prior reports of elusiveness.

abstract click to expand

In a recent article [J. G. Wang, U. Dhumal, M. E. Zakhari, and R. N. Zia, AIChE Journal 72, e70275 (2026).], the authors discuss the absence of simulations of monodisperse hard spheres in which a metastable fluid spontaneously nucleates into a stable fluid-crystal coexistence. Here, we show that such a simulation can be readily accomplished with standard simulation methods.

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cond-mat.soft 2026-05-06

Model shows nanonucleation for polyamorphism near glass transition

Polyamorphism in Glassy Network Materials

Tuned network liquid reproduces water-like phase diagram and predicts tiny domains plus nonclassical kinetics when the transition nears Tg.

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One dramatic feature of network liquids is the emergence at low temperatures and high pressures of polyamorphism, where multiple distinct liquid phases are accessed in a single material. Polyamorphism can arise from the competition between distinct local inherent structures corresponding to bonded and nonbonded ordering. Thermal bond breaking thus can lead to a phase transition often accompanied by thermodynamic anomalies away from the transition itself, such as the familiar density maximum in water at atmospheric pressure and $4^\circ$ C. Water exhibits network interactions in the form of hydrogen bonding between water molecules. The polyamorphic transition in water, however, is difficult to study due to the rapid crystallization of supercooled water and due to glassy effects at low temperatures. In the present work, we propose a simple microscopic model where the glassy and thermodynamic properties are both calculated directly from the microscopic potentials. The model contains a liquid-liquid phase transition, which, after tuning the microscopic parameters, may be located either above, near, or below the glass transition. By applying the Random First Order Transition theory of the glass transition to this simple microscopic model, we shine light on the interplay of polyamorphism and glassy properties in network liquids. We show the connection between the thermodynamic water-like anomalies and corresponding anomalies in the glassy kinetics. The analysis unveils key details on the way glassy dynamics modifies the phase transition kinetics. When the parameters of the model are tuned to produce a phase diagram resembling that of water, the liquid-liquid phase transformation near $T_g$ occurs via ``nanonucleation'', resulting in extremely small domains sizes and nonclassical nucleation kinetics which are predicted from the RFOT theory.

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cond-mat.soft 2026-05-06 3 theorems

Minimal model predicts tracer motion in crowded cells

A framework for modeling and inferring tracer diffusion in crowded environments

Steric and hydrodynamic simulation plus Gaussian process surrogate matches experiments and infers structure orders of magnitude faster

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Tracer diffusion in crowded environments is central to many biological and soft matter systems, but quantitative frameworks for linking tracer motion to environmental structure remain limited. Here, we study the transport of rigid tracers in suspensions of soft particles and within living cells. Experiments reveal a transition from diffusive to confined motion as the matrix area fraction increases. We develop a minimal simulation that incorporates steric exclusion and hydrodynamic hindrance to reproduce the observed mean-squared displacements (MSDs). Using simulation outputs, we train a parallel partial Gaussian process (PPGP) model that rapidly predicts MSDs from matrix geometric variables, including area fraction, particle size, and polydispersity. The PPGP model accelerates predictions by several orders of magnitude relative to simulation and experiments. Analysis reveals that tracer transport is primarily governed by accessible pore sizes and that distinct global structures can produce indistinguishable MSDs. We find that the minimal model can also capture the MSDs of internalized tracer particles in cells. The framework enables rapid inference of structural properties in crowded environments, including transport in the intracellular environment.

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cond-mat.soft 2026-05-06

Two-step yielding occurs in single biopolymer networks too

Linear and Non-Linear Rheology of Single and Double Cross-Linked Biopolymer Networks under Viscous Shear Flow

Double networks' large-strain curves match summed singles while small-strain curves do not, according to shear-flow simulations.

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In this research study, a numerical tool, which is based on a version of Slender Body theory, has been used and also modified to simulate the mechanical behaviour of single- and double-cross-linked biopolymer networks (hydrogel) under oscillatory shear flow. The hydrodynamic interactions among fibres of intertwined networks were considered. Then, the stress and Fourier coefficients (i.e. shear moduli) were evaluated for both linear and nonlinear regimes. It was found that the double peaks (two-step yielding) of two double network at 100% maximum strain amplitude (nonlinear regime) cannot happen due to changes in fibre alignments and seed numbers, although the crosslinkers between two subnetworks present, which was previously reported in the literature. In fact, we also observed two peaks for single network in nonlinear regime. Furthermore, it was shown that the stress-strain curve of double network is not predicted by just superimposing the results from the corresponding single networks at 5% maximum strain amplitude (linear regime), but this prediction can be provided at 100% maximum strain amplitude (nonlinear regime). The Fourier coefficients and corresponding amplitude (an indication of nonlinearity effects) for double network were quite considerable from zero to fifth modes in nonlinear regime, despite enough zero and first modes in linear regime. It was also shown that the nonlinearity effects can be related to the morphology of the initial structure, i.e. the seed number rather than the flow condition for the single network. These results can help scientists to better design enhance fibrous materials used in wound healing or tissue engineering.

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cond-mat.soft 2026-05-06

Adhesion changes sliding mode in smooth soft contacts

Adhesion-controlled sliding and the Stribeck curve in hydrophobic soft contacts

Rough PMMA-PDMS surfaces follow lubrication theory, but smooth adhesive ones show low-speed instabilities that vanish at higher speeds.

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We present an experimental and theoretical study of dry and glycerol-lubricated sliding for polymethyl methacrylate (PMMA) cylinders with different surface roughness sliding on polydimethylsiloxane (PDMS) rubber. This system represents a hydrophobic soft contact, where adhesion may persist even in the presence of the lubricant and thereby modify both the real contact area and the sliding response. Dry-friction measurements, combined with contact-area calculations that include adhesion, provide a baseline for the lubricated study. For the two sandblasted surfaces, the measured Stribeck curves are described reasonably well by a mean-field mixed-lubrication theory with a fitted velocity-independent effective interfacial shear stress. In contrast, the smooth surface exhibits qualitatively different behavior. We attribute this to an adhesion-controlled sliding mode involving macroscopic Schallamach-wave-like instabilities at low sliding speeds, which are progressively suppressed as the sliding speed increases and forced wetting reduces direct solid-solid contact. The results show that, for soft hydrophobic contacts, the Stribeck curve cannot always be understood from classical fluid flow and load sharing alone. For sufficiently smooth and adhesive surfaces, adhesion changes not only the real contact area but also the sliding mode itself.

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cond-mat.soft 2026-05-06

Interstitial gas changes granular transport coefficients

Dynamic properties of a confined quasi-two-dimensional granular fluid driven by a stochastic bath with friction

Viscous drag and random forcing modify viscosity and conductivity relative to dry granular systems

abstract click to expand

This paper investigates the dynamic properties of a confined quasi-two-dimensional granular fluid at moderate densities, modeled within the framework of the Enskog kinetic equation. The system is described using the so-called $\Delta$-model, which incorporates energy injection through modified collision rules, and is further extended to account for the influence of an interstitial gas via a viscous drag force and a stochastic Langevin-like term. By applying the Chapman-Enskog method, the Navier-Stokes transport coefficients and the cooling rate are derived analytically considering the leading terms in a Sonine polynomial expansion. The study focuses on steady-state conditions and examines how the combined effects of inelastic collisions and external driving influence transport properties such as the viscosity and the thermal conductivity. Theoretical predictions for the steady temperature and the kurtosis are validated against direct simulation Monte Carlo (DSMC) results, showing excellent agreement. The findings reveal that the external driving significantly alters the transport coefficients compared to dry (no gas phase) granular systems, challenging previous assumptions that neglected these effects. Additionally, a linear stability analysis demonstrates that the homogeneous steady state is stable across the explored parameter space.

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cond-mat.soft 2026-05-06

Chiral active fluids sparkle with unstable rotating bubbles

Sparkling bubbles in chiral active fluids

At optimal densities bubbles form but repeatedly break and reform, according to hydrodynamic theory from odd transverse forces.

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We study an inertial chiral active fluid, formed by repulsive particles that transfer angular momentum through odd interactions, i.e. transverse forces. Chirality induces an inhomogeneous phase, consisting of rotating bubbles, whose formation is favored at an optimal packing fraction. In this regime, we discover that bubbles may be dynamically unstable, breaking up and reforming in the steady state, thereby showing a spontaneous sparkling-like behavior reminiscent of supersaturated liquids. Bubbles and sparkling bubbles are predicted by a coarse-grained hydrodynamic theory, revealing the intrinsic non-linearity of these collective phenomena, and call for experimental verifications in granular spinners or spinning colloids.

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cond-mat.soft 2026-05-05

Curvature sensitizes vesicle undulations to membrane viscosity

Equilibrium fluctuations of a quasi-spherical vesicle: role of the membrane dissipation

Theory shows faster lipid density relaxation without the stretched-exponential regime of planar membranes

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We theoretically investigate the thermally-driven curvature and lipid density fluctuations of a quasi-spherical vesicle, accounting for the dissipation due to monolayer viscosity and intermonolayer friction. The theory predicts that membrane curvature makes long-wavelength undulations sensitive to membrane viscosity and speeds up the relaxation of the lipid density fluctuations. Implications for the dynamic roughness and Dynamic Structure Factor measurements of submicron liposomes on nano-second time scales are discussed. Specifically, a clear stretched-exponential relaxation regime may not exist, in contrast to the behavior of planar membranes for which an anomalous diffusion exponent of 2/3 has been predicted [Zilman and Granek, Phys. Rev. Lett. (1996)].

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cond-mat.soft 2026-05-05

Multistable landscapes let micro-machines adapt under one field

Multistable energy landscapes for adaptive microscopic machines

Internal state selects which function runs when the external magnetic drive stays unchanged

abstract click to expand

The past few years have seen great strides in our ability to build synthetic microscopic machines. However, the function of such machines is often controlled directly by externally applied fields that deterministically specify the instantaneous machine dynamics. A crucial step towards machines that can respond adaptively to changes in their environment is the ability to program multiple functions that actuate under the same external driving field, so that their internal state dictates which function is executed. Here, we demonstrate that energy landscapes with designed multistability enable the same externally applied field to drive multiple configurations and dynamic responses in microscopic machines, enabling increasing levels of autonomy. We show three examples. First, we write a bistable energy landscape into a microscopic device, enabling the device to exhibit two stable mechanical configurations under the same external magnetic field. Next, adding a second degree of freedom enables differing dynamic responses to the same external magnetic field, which we direct into net displacement of the environment. Finally, we demonstrate how a microscopic machine with a continuous symmetry autonomously channels a single degree-of-freedom magnetic actuation into locomotion and adaptively responds to forces induced by other machines.

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cond-mat.soft 2026-05-05

Noise transition in active colloids depends on density but pinning does not

Emergent flocking dynamics in chemorepulsive active colloids: interplay of disorder and noise

Polar order survives higher noise levels at higher densities, while the pinning fraction needed to destroy order stays fixed.

abstract click to expand

Recent studies of active colloidal matter have revealed that a global polar order can arise from chemorepulsive interactions among particles without any explicit alignment interaction between them. In this work, we investigate such chemically interacting active colloids in the presence of quenched disorder, where a fraction of particles are randomly pinned in space. These pinned particles are restricted to rotational motion while remaining chemically coupled to the mobile population. In addition, angular noise is incorporated into the rotational dynamics to capture stochastic effects. To elucidate the interplay of quenched disorder and noise, we construct phase diagrams based on polar order and its fluctuations, and systematically analyze the associated disorder- and noise-driven phase transitions. Surprisingly, we find that the phase transition driven by the noise is significantly dependent on the density of the particles, whereas such a density-dependence is not present when the control parameter is the pinning fraction. The finite-size effects on these transitions are also examined. An effective interaction range, governed by the coefficient related to screening of the chemorepulsive interaction, plays a crucial role in collective behavior. When the effective interaction range is much smaller than the system size, the system exhibits density band formation, a feature absent in the long-range interaction regime. Moreover, near the transition point, the order parameter distribution becomes bimodal for the case of short-range interaction.

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cond-mat.soft 2026-05-05

Matching domain and particle sizes boosts disk adsorption

Equilibrium Adsorption of Hard Disks on Patterned Adhesive Surfaces: A Monte Carlo Simulation Study

Monte Carlo simulations show pattern geometry raises adsorption at intermediate chemical potentials when domains equal disk diameter, before

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Equilibrium adsorption of disk-like particles on patterned adhesive surfaces is studied using Monte Carlo simulations. The surface is represented as a two-dimensional plane with circular adhesive domains arranged either regularly or randomly, while the particles are modelled as hard disks. The interaction energy between a particle and the surface is defined by the contact area between the particle and the adhesive domains. It is shown that the adsorption behaviour is controlled not only by the total area of the adhesive regions, but also by the geometry of the surface pattern. In particular, the domain size is found to have a significant effect on the adsorption efficiency. The most pronounced effect is observed when the particle and domain sizes are equal, which leads to enhanced adsorption at intermediate values of the chemical potential. At high values of the chemical potential, however, when the particle surface coverage increases, steric effects become important, which weakens the influence of the surface pattern geometry. The obtained results demonstrate that the adsorption efficiency and surface organization of particles can be tuned by choosing the size, coverage, and spatial arrangement of adhesive domains. This study may be useful in the design of functional surfaces, selective adsorption platforms, biosensors, and affinity-based cell sorting systems.

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cond-mat.soft 2026-05-05

Knot probability in polymer films peaks at chain-size thickness

Polymer Knots in Thin Films: Thickness Dependence, Local Effects, and Stiffness

It vanishes in thinner films, recovers in thicker ones, and arises from flattening and longer entanglements near the walls.

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We study how confinement affects topology and conformations in polymer films of varying thickness $h$. The knotting probability exhibits a maximum at intermediate thicknesses near the bulk radius of gyration $h \approx R_\mathrm{g,bulk}$, vanishes at small $h$ and approaches bulk values for large $h$. Close to walls, the entanglement length increases monotonically and conformations become flatter. A layer-resolved analysis of structural and topological properties allows us to reconstruct the explicit thickness dependencies by integrating layer-resolved properties of a thick film.

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cond-mat.soft 2026-05-05 3 theorems

Rod shape and density dictate swarming

Shape anisotropy governs organization of active rods: Swarming, turbulence, flocking, and jamming

Light-driven rod experiments show aspect ratio and area fraction alone control shifts between these collective states.

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Shape anisotropy of individual building blocks plays a crucial role in creating exotic structures and controlling phase behavior in equilibrium systems. We present a combined experimental and simulation study in which we used light-driven self-propelled rods to investigate when and how shape-induced alignment and steric and hydrodynamic interactions govern self-organization. Varying rod aspect ratio and area fraction causes the system to evolve from active Brownian motion to swarming, active turbulence, flocking, large clusters, and jamming. A state diagram summarizes emergent behaviors, and spatiotemporal analyses reveal distinct giant-number fluctuations across states. This minimal model offers insight into the self-organization of biological rodlike microswimmers, enabling the decoupling of physical from biological mechanisms. Our results provide design rules for programmable synthetic active materials and highlight parallels with bacterial swarms and other biological assemblies.

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cond-mat.soft 2026-05-05 3 theorems

Odd elasticity suppresses square bifurcations under tension

Nonlinear isotropic odd elasticity

In 2D, nonconservative responses eliminate the instabilities of the classic Rivlin problem; 3D versions retain them despite no linear oddity

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The nonconservative elastic responses of active solids have driven a recent explosion of interest in two-dimensional "odd" elasticity: small, linear deformations of these Cauchy elastic solids enable new behaviour absent from classical, passive elasticity. Here, we establish the description of large, nonlinear deformations of isotropic two-dimensional Cauchy elastic solids. We apply our framework to the Rivlin problem, perhaps the simplest problem of elasticity lacking a linear analogue: a square deforms under dead load tractions. Surprisingly, we find that oddness suppresses the bifurcations of a passive Rivlin square. By contrast, we discover that the bifurcations of a three-dimensional Rivlin cube survive oddness even though there is no isotropic, odd linear elasticity in three dimensions. Our results thus form the basis for describing large deformations of active, biological solids while revealing their unexpected nonlinear behaviour that arises even in minimal problems.

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cond-mat.soft 2026-05-05 3 theorems

Diffusio-osmosis drives flows in nanochannels without semi-permeable walls

Diffusio-osmotic transport in nanochannels

Entropic forces in boundary layers produce the same transport as classical osmosis, removing the need for membrane selectivity and enabling

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In this chapter, I will enter into the roots of entropically-driven transport with a focus on diffusio-osmotic transport in nanochannels. Diffusio-osmosis is a subtle surface transport, originating in entropic driving forces occuring within the diffuse layers at solid boundaries. Specifying diffusio-osmosis to nanochannels may first look like a marginal refinement, yet it reveals that osmotic drivings can arise in channels and membranes without the prerequisite of semi-permeability, so that diffusio-osmosis extends the domain of existence of entropically driven transport. Osmosis and diffusio-osmosis are two faces of the same phenomenon, naturally embedded in an Onsager framework and quantified by local and global force balances. This perspective clarifies why nanochannels are privileged arenas where diffusio-osmosis and its consequence do flourish. Throughout the chapter, I discuss a set of conceptually relevant examples to show how diffusio-osmosis "pops up" in various situations: as enhanced diffusion, mechano-sensitivity, rectified osmotic flows and, ultimately, as a lever for osmotic energy conversion from single nanopores to membrane modules approaching industrial reality.

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cond-mat.soft 2026-05-05 2 theorems

Clustering changes composite stress fields at fixed volume

Quantifying the effects of particle clustering in random thermoelastic composites -- numerical and mean-field analyses

Mean-field cluster model matches full simulations by showing nearest-neighbor distance alters local strains and effective thermoelasticity

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The effect of space distribution of randomly-placed particles in a representative composite volume on the thermoelastic effective properties and local stress and strain distribution is analyzed. Quantitative assessment is performed using both the full-field finite element analyses and the mean-field interaction model, known also as a ''cluster'' model. The latter model is developed in the multi-family setting enabling one to study the mean stress and strain separately for each inclusion of the representative unit cell. The particles are assumed to be spherical and of equal size, while considered examples differ by the volume fraction of inclusions and mean nearest-neighbour distances.

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cond-mat.soft 2026-05-04

Bond strength selects three distinct assembly paths for cubic colloids

Unraveling and controlling the self-assembly pathways of cubic colloids

Small-cluster tracking shows how increasing attraction switches from reorganization-driven crystals to diffusion-limited arrested clusters,

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The self-assembly of anisotropic building blocks into complex spatial architectures is an important design strategy in material science but the mechanisms by which the anisotropic interactions influence the early-stage growth and formation of disordered (non-)equilibrium structures remain poorly understood. Here, we experimentally demonstrate that tuning the strength of shape-induced directional bonds changes the self-assembly pathways of cubic colloids. By tracking the growth kinetics and internal reorganizations of small clusters at increasing attraction strength, we identify three self-assembly regimes: (i) nucleation and growth regime: slow reorganization-dominated growth of crystalline clusters, (ii) dynamic regime: diffusion-limited growth with dynamic cube reorganizations leading to disordered crystalline clusters and (iii) static regime: diffusion-limited growth of kinetically arrested clusters unable to reorganize due to directional bonding constraints. We further show that transitions between these regimes are reversible and allow pathway engineering to control the structure and disorder. Our results reveal how directional bonding governs pathway selection, providing important insights for the rational design of reconfigurable colloidal, nano-, and biomaterials.

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cond-mat.soft 2026-05-04

Dual heterogeneity shifts membrane trade-off to higher permeability at fixed rejection

Hindered transport of spherical particles in cylindrical pores: The role of structural heterogeneity in rejection-permeability trade-offs

Coupled size variations in pores and particles widen local flow conditions and expand the attainable selectivity-throughput space.

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Membrane separations rely on balancing rejection and permeability. Extensive work has clarified how pore structure and operating conditions control each quantity in idealized or weakly heterogeneous systems. However, it remains unclear how this trade-off emerges in strongly heterogeneous media, where coupled distributions of pore and particle sizes shape the local balance between advection and diffusion and generate substantial variability in performance among distribution realizations. Here we present a steric hindered-transport framework for spherical particles in cylindrical pores that explicitly resolves both single and coupled dual heterogeneity in size distributions. We show that the ensemble-averaged rejection increases with the particle-pore aspect ratio $\lambda$ and with the P\'eclet number $Pe$, while advection enhances steric exclusion by up to $\sim$20\% at intermediate $\lambda$. Dual heterogeneity broadens the distribution of effective $Pe$, increases the variability and incidence of anomalous rejection trends, while systematically shifting the rejection-permeability trade-off toward higher permeability at fixed rejection. These results suggest that controlled heterogeneity can serve as a design lever to expand the attainable operating space for simultaneous high selectivity and high throughput.

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cond-mat.soft 2026-05-04

Dimples encode reprogrammable hinges for origami

Dimple-Encoded Reprogrammable Origami

One elastic sheet folds into triangles, squares or cubes by selectively inverting dimples to set hinge angles

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Programmable folding of elastic sheets typically relies on predefined flexible creases or active materials-enabled hinges, which lack intrinsic bistability and limit reprogrammability within a single structure. Here, we present a dimple-encoded origami platform that converts bistable dimple snapping into spatially addressable hinges with prescribed folding angles in a continuous sheet. This interaction-enabled mechanism enables the design of distributed hinge networks through the arrangement and selective inversion of dimples. We establish folding-angle design charts that can be directly used to select local dimple arrangements for target fold angle, forming a practical hinge library without altering the underlying unit geometry. Using this approach, a single dimpled sheet can be reprogrammed to realize multiple distinct configurations, such as triangle, square, and pentagon shapes. We further extend the method to flat-to-3D morphing of polyhedral origami and validate the results through experiments and finite element simulations. As demonstrations, we realize self-supporting cubic shells with enhanced impact resistance and partially deployable cube configurations that remain stable upon opening, highlighting their potential for protective enclosures and deployable architectural structures. The proposed strategy provides a fabrication-friendly route to reprogrammable shape-morphing and adaptive mechanical systems.

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cond-mat.soft 2026-05-04

DNA oligomers set colloidal layer count and composition

Colloidal layer deposition with a controllable number of layers and compositional order

Equilibrium fixes thickness while reaction speeds keep particle types on separate planes in surface-triggered assembly.

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We design a system with a binary suspension of colloids and a surface that triggers the self-assembly of crystallites with a finite thickness. The proposed design allows controlling the number of layers forming the aggregate and constrains the two types of particles to lie on different planes. These functionalities are achieved by decorating the colloids and the surface with multiple DNA oligomers featuring specific interactions. The surface triggers a chain of reactions between DNA oligomers, leading to localized self-assembly. Equilibrium principles control the thickness of the aggregates. Instead, compositional order is achieved by engineering the reaction kinetics between DNA oligomers in a way that limits interactions between colloids of the same type. We validate our design using theory and reaction-diffusion simulation algorithms, which capture the multibody nature of the interactions. This work demonstrates how engineering the kinetics provides a new avenue for controlling the morphology of aggregates assembled by DNA.

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cond-mat.soft 2026-05-04

Inverse density as ħ refines polymer phase separation binodals

Loop expansion in polymer field theory: application to phase separation

The leading correction improves dilute-phase coexistence density over RPA while critical point error stays similar, according to simulations

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Liquid-liquid phase separation underlies phenomena ranging from protein condensate formation to the phase coexistence of synthetic polymers. Although the random phase approximation (RPA) is widely used to predict such phase behavior, its quantitative accuracy for binodals of polymer solutions, particularly outside the high-density regime, remains incompletely characterized. Here, we develop a field theoretic loop expansion in homopolymer systems by identifying the inverse polymer density $\rho^{-1}$ as the Planck constant $\hbar$ in quantum field theory. We calculate the leading-order and next-to-leading-order corrections to the RPA free energy, denoted as RPA+ and RPA++, respectively. Testing the binodal predicted by the RPA+ against molecular dynamics simulations of bead-spring chains with Gaussian pair interactions, we find that the RPA+ qualitatively improves the dilute-phase coexistence density over the RPA, while the critical point error remains comparable to that of the RPA. Our results establish the loop expansion as a systematic route for refining the RPA-based binodal predictions for polymer phase separation.

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cond-mat.soft 2026-05-04

Graphite nanoslits turn pressure into ionic signals via inlet charging

Architecting mechanosensitive nanofluidic transport in graphite nanoslits

Selective surface charge lets flowing water carry excess ions to modulate conductance without deformation.

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Mechanosensitive ion transport plays a central role in enabling living systems to perceive and adapt to their environment through the deformation of soft, embedded ion channels. In this work, we demonstrate that ion transport within a two-dimensional graphite nanoslit can be rationally engineered to achieve a bipolar, pressure-sensitive response without any structural deformation. The mechanosensitivity arises from the selective charging of one channel inlet, which acts as a reversible source of mobile charge carriers. These excess-ions can then be advected in or out of the channel by the pressure-driven water flow, thereby modulating the ionic conductance. This mechanism is captured through a comprehensive electrohydrodynamic model that analytically accounts for coupled diffusion, convection, surface transport, diffusio-osmosis, and interfacial slippage, both inside and outside the nanoslit. The theoretical framework quantitatively reproduces the experimental data, showing that a simple surface charge pattern can give rise to complex, pressure-dependent conductance. These findings reveal how rich nonlinear couplings at the nanoscale can be harnessed to design adaptive, bioinspired nanofluidic systems, exemplified here by ionic pressure sensors.

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cond-mat.soft 2026-05-04

Channel geometry inhibits ion dispersion for enhanced separation

Dispersion of multiple charged species in an axially symmetric slowly varying channel

Self-induced electric fields in slowly varying channels lead to non-monotonic number of theoretical plates.

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The transport and dispersion of multiple species of charged ions are central to many biological and physical processes, including electrokinetic ion separation. However, most theoretical studies of dispersion in channels have focused on neutral solutes, leaving the transport of multiple charged species comparatively unexplored. Differences in ionic diffusivities in a multispecies electrolyte solution generate an self-induced electric fields that drive electromigration. To capture these effects at the macroscopic scale, we combine the lubrication approximation with homogenization theory, under electroneutrality and zero-current constraints, to derive an effective transport equation governing the cross-sectionally averaged concentrations. We apply our model framework to a range of channel geometries and compute the resulting effective dispersion coefficients. Finally, we investigate how channel geometry can be tuned to enhance ionic separation. We observe a geometry-induced electro-diffusive coupling that inhibits solute dispersion in certain channels, leading to a non-monotonic Number of Theoretical Plates (NTP) and making such channels ideal for separation processes.

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cond-mat.soft 2026-05-04

Pre-charged polymers hand ions to droplets and speed their motion

Pre-charging polymer surfaces enhances droplet mobility and electrification

Charge picked up by droplets matches deposited amount for moderate densities and contact angles fall, easing movement on the surface.

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Surface-bound electric charge on polymer materials can strongly influence droplet behaviour and solid-liquid charge transfer, but the mechanisms and the means to control these effects remain unclear. In this work, we systematically controlled the surface charge on polymer surfaces, including polytetrafluoroethylene (PTFE) and Nylon-66, by first neutralising the surfaces with an anti-static ion blower and then applying charge using an ion gun. We find that droplets pick up pre-deposited surface ions during the first wetting of the surface, and that the transferred charge directly correlates with the deposited charge encountered by the wetted area for moderate deposited densities (|{\sigma}_d |<40 {\mu}C/m2) independent of material properties. We also demonstrate that the deposited charge reduces contact angle and increases contact-line mobility in a manner consistent with an increase in effective solid surface energy. For higher surface charge densities, we observe instabilities such as droplet splitting or detachment. This work demonstrates an effective approach to control solid-liquid electrification, enabling amplification or suppression of surface charge and the directed manipulation of fluid motion on surfaces.

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cond-mat.soft 2026-05-04

Neural network ranks structural descriptors for supercooled water

Machine learning evaluation of structural descriptors for supercooled water

Temperature classification task shows which local order parameters best capture changes in hydrogen-bond networks.

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The anomalous behavior of liquid water is widely associated with a liquid-liquid phase transition between high- and low-density states in the supercooled regime. At the microscopic level, tetrahedral hydrogen-bond networks govern these properties, motivating structural descriptors that characterize local molecular environments. These structural descriptors quantify features such as tetrahedral order, local density, and the separation between the first and second coordination shells; however, they have largely been proposed independently, with limited systematic comparison. Here we evaluate 16 previously proposed descriptors using a neural-network-based temperature classification framework, enabling an objective assessment of their ability to distinguish temperature-dependent structural changes in supercooled water. We further apply an explainable artificial intelligence method that identifies the structural features responsible for the model predictions. This approach reveals how different descriptors encode local structural information and establishes a data-driven framework for benchmarking structural descriptors in liquid water.

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cond-mat.soft 2026-05-01

Block copolymer nanodroplets switch between multiple surface structures

Surface-Adsorbed Nanodroplets of Symmetric Diblock Copolymers Form Versatile and Stimuli-Responsive Nanostructures

Symmetric diblocks form reversible patterns on surfaces that change with surfactant addition or temperature.

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Block copolymers often create droplets when placed on a substrate. Such nanostructured droplets can be arranged into regular microstructured arrays, thereby forming hierarchically organized materials that can be used in microelectronics, plasmonics, sensing, photonics, metamaterials production, and even cryptography. However, it is unclear if such materials can be stimuli-responsive, i.e., be able to change their nanostructure on a single droplet level upon applying external stimuli. In this work, we discovered that small (10-100 nm) surface-adsorbed droplets of symmetric diblock copolymers can form a multitude of different externally switchable nanostructures. We obtained a near-equilibrium, comprehensive 4D diagram of droplet morphologies by performing large-scale self-consistent field theory (SCFT) calculations under various wetting and phase separation conditions. The SCFT modeling was augmented with a computational algorithm that established an equilibrium droplet morphology in a given system without assuming potentially equilibrium structures prior to simulation. The discovered droplet nanostructures agreed excellently with previously published experimental data. Crucially, we showed that direct and reversible transitions between different droplet morphologies are possible upon changing the interaction strength between components, which can be tuned externally in experiments by adding surfactants or controlling temperature. We confirmed experimental realizability of such stimuli-responsiveness by modeling surfactant addition that led to a switch between droplet nanostructures. This work demonstrates that even the simplest symmetric diblock copolymers are able to produce versatile and stimuli-responsive structures on a surface when confined to a small nanodroplet. This opens the possibility to produce smart coatings with externally switchable hierarchical micro- and nanostructures.

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cond-mat.soft 2026-05-01 2 theorems

Model simulates gas cluster ripening in sandstone over 48 hours

Time-dependent pore-network modelling of Ostwald ripening in porous media

It reproduces lab observations of ganglion changes and enables predictions of trapped saturation for hydrogen and CO2 storage.

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We present a time-dependent pore-network model that couples transient mass transfer in the aqueous phase, capillary pressure heterogeneity, and realistic pore-throat geometries to capture the dynamic evolution of gas clusters during Ostwald ripening in porous media. The model is applied to Bentheimer sandstone to study Ostwald ripening after imbibition to residual gas saturation. Both imbibition (shrinkage) and drainage (growth) events occur as the local capillary pressure in trapped gas clusters approaches equilibrium. The model tracks event statistics, capillary pressure equilibration, cluster volume distributions, and spatial saturation profiles over 48 hours. While the volume-weighted average capillary pressure is constant, there is a rapid initial decline in average number-weighted cluster pressure and a shift in cluster size distributions toward fewer, larger ganglia, consistent with pore-scale imaging studies. Pore and throat occupancy analysis reveal persistent gas trapping in larger pore spaces. Since growth is by drainage, the pore-scale configuration of fluid is different from that predicted by an equilibrium percolation-without-trapping model that only allows imbibition events. The model reproduces displacement and ganglion rearrangement during time-limited laboratory experiments, and can then provide predictions of trapped saturation, relative permeability and capillary pressure under field-scale conditions with application to hydrogen, natural gas and carbon dioxide storage in the subsurface.

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cond-mat.soft 2026-05-01

Emulsion yield stress grows as E squared in high-frequency regime

Insights into the electrorheological and electrohydrodynamic regimes in electrically driven emulsion

Data collapse and microrheology agreement show scale-independent electrorheological response distinct from one-second electrohydrodynamic re

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Recently, we reported the electrorheoimaging (ERI) technique (Bahraminasr et al, 2026), and found that frequency-dependent electric field of an oil-in-oil emulsion yields two distinct regimes: a high-frequency dipolar, electrorheological (ER) regime and a low-frequency electrohydrodynamic (EHD) regime. In this work, we identify a phenomenological model to fit the results in the ER regime to a classic yield-stress fluid, and find collapse onto a master curve upon rescaling, consistent with a yield stress that grows approximately as $E^2$. Macroscopic small-amplitude oscillatory shear (SAOS) rheology is compared with passive microrheology employing differential dynamic microscopy (DDM), with the close agreement implying scale independence of the ER behaviour, and indicating that, unlike steady shear, SAOS measurements do not restructure these samples and probe underlying material properties. Finally, under the presence of both steady shear and electric fields in the EHD regime, the emulsion forms banded structures composed of alternating droplet-rich and droplet-depleted regions. We explore recurrence and divergence in the location of these bands: they emerge within seconds of field application and decay rapidly after the field is switched off. Using the Jensen--Shannon divergence between radial intensity profiles, we show that the driven structure loses memory on timescales of order $1~s$ commensurate with the timescale of the EHD convection roll. For much longer field-off intervals successive banding events become statistically independent.

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cond-mat.soft 2026-05-01

Neural net maps Vicsek phases at 0.92 accuracy

Mapping the Phase Diagram of the Vicsek Model with Machine Learning

Clustering simulation observables reveals a narrow coexistence region and extends boundaries beyond sampled points.

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In this study, we use machine learning to classify and interpolate the phase structure of the Vicsek flocking model across the three-dimensional parameter space $(\eta,\rho,v_0)$. We construct a dataset of simulated parameter points and characterize each point using long-time dynamical observables. These observables are then used as inputs to a K-Means clustering procedure, which assigns each point to a disorder, order, or coexistence phase. Using these clustered labels, we train a neural-network classifier to learn the mapping from model parameters to phase behavior, achieving a classification accuracy of 0.92. The resulting phase map resolves a narrow coexistence region separating the ordered and disordered phases and extends the inferred phase boundaries beyond the originally sampled simulation points. More broadly, this approach provides a systematic way to convert sparse simulation data into a global phase diagram for collective-motion models.

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cond-mat.soft 2026-05-01

Active phase separation propels colloids indefinitely

Propelling catalytic structures using active phase separation

A protein-enzyme cycle nucleates condensates that repel and drive micron-sized particles in uniform environments at up to 100 μm/s.

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Living systems routinely consume energy to achieve motility, often using intricate biomolecular machinery. In this work, we show that active droplets can sustain indefinite self-propulsion of a spherical colloid in an otherwise homogeneous, isotropic, and autonomous environment. Our proposed minimal mechanism consists of phase-separating proteins, enzymes passivating them, and complementary enzymes anchored to the colloid surface that reactivate the proteins. This passivation-activation cycle gives rise to a symmetry breaking - nucleation and stabilization of a condensate near the colloid surface, which in turn exerts a repulsive force on the colloid. We numerically demonstrate that this mechanism can propel micron-sized colloids at speeds of up to a hundred microns per second. This propulsion mode is strongly resistant to Brownian fluctuations and external forces, suggesting that propulsion mechanisms based on biomolecular condensates may offer a complementary, motor-free route to biological transport.

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cond-mat.soft 2026-05-01

Ultrasound shifts shear thickening to higher shear rates

Acoustic modulation of shear thickening transition in dense adhesive suspensions

Rather than lowering viscosity, acoustic waves destabilize force networks so jamming requires stronger shear.

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Discontinuous shear thickening (DST) in dense suspensions leads to flow instabilities that limit processing in many systems. While high-power ultrasound has been reported to reduce the apparent viscosity of such materials, the origin of this effect remains unclear. Here, we investigate dense adhesive cornstarch suspensions, where shear thickening arises from fragile, load-bearing force networks embedded in heterogeneous density-wave structures. Using a rheo-ultrasound setup, we show that ultrasound does not directly reduce viscosity but instead shifts the shear-thickening transition toward higher shear rates. This is evidenced by the collapse of stress probability distributions onto master curves, revealing a continuous evolution toward more fluid-like states without a sharp threshold. We interpret these results through a separation of time scales, in which the suspension behaves as an effectively immobile porous medium subjected to high-frequency interstitial flows. Fluidization then arises from a combination of boundary slip, bulk destabilization of force networks by drag-force fluctuations, and localized acoustic streaming. Beyond these mechanisms, we propose that ultrasound modifies the stability of force networks by introducing fluctuating hydrodynamic forces at the pore scale. As a result, larger stresses or shear rates are required to sustain jammed states, leading to a continuous renormalization of the DST transition. These findings provide a consistent physical picture of acoustic fluidization in adhesive suspensions and establish ultrasound as a powerful tool to control discontinuous shear thickening in confined flows.

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cond-mat.soft 2026-05-01

Cyanobacterial colonies resist lake mixing forces

On Linear and Non-Linear Mechanics of Cyanobacterial Colonies

Tensile strengths match biofilms and rise under low phosphorus, far above typical hydrodynamic stresses.

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Toxic cyanobacterial blooms are a growing environmental concern that affects freshwater ecosystems, drinking water supplies, and public health. The cyanobacterium Microcystis is among the most important bloom forming species. It often grows in large colonies, which enhances its flotation, reduces grazing, and improves nutrient regulation. Microcystis cells are held together by a matrix of extracellular polymeric substances (EPS), making colony mechanics crucial for bloom formation. However, an analysis of the biomechanical properties of cyanobacterial colonies, and how these properties relate to environmental conditions like nutrient availability, remains largely missing. Here, we use micropipette force sensors to quantify the linear and non-linear mechanical properties of individual colonies at single-cell resolution. Bulk shear rheology complements these measurements by probing macroscopic properties. The measured tensile strength and yield stress are broadly comparable to those of bacterial biofilms and are far greater than the hydrodynamic stresses typically found in wind-mixed lakes. This implies that cyanobacterial colonies are highly resistant to fragmentation by natural mixing processes. We also show that low nutrient availability, particularly low phosphorus, produced stronger colonies, suggesting structural changes in the EPS. Overall, our results establish mechanical testing as a tool for a more complete and physically grounded understanding of cyanobacterial colony formation.

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cond-mat.soft 2026-05-01

Guided waves in elastomer strips extend mechanical testing past rheometer limits

Guided elastic waves for soft elastomer characterization: an alternative to conventional rheometry

Dispersion curves measured under stretch are matched to a coupled viscoelastic-acoustoelastic model to obtain broadband parameters that stay

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Elastic wave propagation is intrinsically sensitive to the mechanical properties of the medium through which it travels. In soft elastomers, this makes guided elastic waves natural probes of viscoelastic and acoustoelastic behavior over a broad frequency range. In this work, we introduce a wave-based mechanical characterization method in which a thin elastomer strip acts as a waveguide supporting multiple in-plane guided modes. By combining stroboscopic measurements of monochromatic wave fields with a theoretical framework that couples frequency-dependent viscoelasticity and elongation-dependent acoustoelasticity, we extract complex-valued dispersion relations for guided modes under controlled static elongation. A dedicated numerical implementation allows these experimental dispersion curves to be quantitatively matched to theory, enabling identification of the material's rheological and hyperelastic parameters. Applied to several commercial silicone elastomers, the method yields mechanical parameters that are consistent with conventional plate-plate rheometry, while extending the accessible frequency range beyond that of conventional techniques. By exploiting the richness of guided-wave dispersion and the sensitivity of waves to both frequency and pre-stress, this approach provides a unified, broadband, and experimentally simple route to the mechanical characterization of soft elastomers.

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cond-mat.soft 2026-05-01

Asymmetric particle fluxes drive directional cluster migration in vibrated compartments

Directional Cluster Migration Driven by Escape-Rate Asymmetry in Multi-Compartment Granular Systems

Small particles increase large-particle escape rates while large particles decrease small-particle rates, producing net transport without an

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Granular materials are inherently out-of-equilibrium systems due to energy dissipation through inelastic collisions and friction. When driven by mechanical agitation such as vibration, they exhibit rich collective behaviors including segregation, clustering, and spontaneous oscillations. Here, we report directional stepwise migration of particle clusters from one compartment to the next in a vertically vibrated granular system composed of small and large particles. To clarify the underlying mechanism, we directly measured how the flux of both particle species depends on the instantaneous particle populations. The measurements reveal an asymmetric interaction between particle species: the flux of small particles is enhanced by the presence of large particles, whereas that of large particles is suppressed by small particles. A minimal flux model incorporating these measured fluxes reproduces the observed directional dynamics and provides an experimentally grounded framework for collective transport in vibrated granular systems.

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cond-mat.soft 2026-05-01

Jacob's ladder toy shows annihilating topological kink waves

Topological antiqued mechanical toy

Gravity bistability and symmetric strings allow kink-antikink coexistence and pair annihilation forbidden in standard chains.

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{\it Jacob's ladder} -- a classic children's toy -- is a simple mechanical frame comprising rigid blocks connected by strings that shows curious unidirectional flipping waves. Nonetheless, its physical origin remains elusive. By combining experiment, numeral simulation, and theory, we show that understanding the underlying design principle of this toy requires diverse physical ideas. First, we conduct a water-tank experiment that excludes the domino-like mechanism, thus defying widespread expectations. Subsequently, we analytically demonstrate that the toy is bistable under gravity, thus implying its kink wave as a class of topological solitons. The waves are surprisingly reminiscent -- both experimentally and theoretically -- to those in the Kane--Lubensky topological chain, owing to the stiffening of zero modes by the pretension under gravity. However, a close examination based on the index theorem reveals that the similarity remains superficial and that the floppiness of the toy underlies the kink and antikink coexistence -- a forbidden mode in the topological chain. By analyzing a generalized asymmetric toy, we reveal that its symmetric connection renders it topologically singular, thus resulting in amusing motions. We demonstrate these ideas by experimentally observing a dramatic pair annihilation of kink and antikink waves.

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cond-mat.soft 2026-05-01

Viscoelastic microswimmers reverse direction at critical frequency

Propulsion and far-field hydrodynamics of linked-sphere microswimmers with viscoelastic deformability

Four-sphere linked designs change swimming direction when actuation frequency crosses a threshold set by body relaxation time.

abstract click to expand

Viscoelasticity governs the locomotion strategies of deformable microorganisms, rendering it a fundamental mechanical property of microbial motility and an integral component in the design of envisioned microbots. Recent studies have shown that it can enable effective propulsion through non-reciprocal body deformations, even under time-reversible actuation. In this work, we investigate the dynamics of model microswimmers driven by reciprocal actuation, wherein the passive body exhibits viscoelastic deformability. We consider two linked-sphere designs, distinguished by the location of actuation: applied at one end (3-sphere design) or at the midpoint of the swimmer body (4-sphere design). Adopting Kelvin-Voigt deformability, we characterize the kinematic performance of both designs: the three-sphere swimmer possesses an optimal actuation frequency, while the four-sphere swimmer exhibits a critical frequency at which the locomotion direction reverses. We examine the swimmer's far-field hydrodynamic signature and find that resulting flow field is characterized by dominant dipolar and quadrupolar contributions, whose magnitudes are sensitive to the relative length of the actuator segment.

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cond-mat.soft 2026-04-30

Light and magnets program tunable random walks in active particles

Programmable Persistent Random Walks in Active Brownian Particles Govern Emergent Dynamics

This setup lets particles switch motion modes on demand and steer complex paths while changing how they cluster.

abstract click to expand

Self-propelled particles serve as minimal models for emulating the dynamic self-organization of microorganisms, yet most synthetic systems remain limited to a single mode of motion, namely active Brownian particles (ABPs). Here, we present an experimental strategy to encode various persistent random walks in ABPs by combining light-modulated propulsion strength with magnetic control of propulsion direction. Our system enables programmable Levy walks with tunable step-length distributions, run-and-tumble dynamics, self-avoiding random walks, and Gaussian walks, with on-demand switching between motion modes within a single experiment. In addition, particles are steered along complex trajectories such as Fibonacci spirals and nested polygons. Beyond single-particle behavior, we show that propulsion modes influence clustering dynamics by comparing ABPs with chiral active particles undergoing circular motion. These results establish a versatile platform for investigating how encoded motion at the level of individual particles governs transport, search strategies, and emergent organization in active matter systems.

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cond-mat.soft 2026-04-30

Point force deforms thin gel film only near contact

Linear poroelastic response of thin permeable gel films

Poroelastic layer on rigid substrate confines response to distance of order the thickness, supplying closed-form predictions for evolving 3D

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When a hydrophilic and deformable porous material is immersed in a bath, it may absorb the solvent and expand by several times its volume, thus forming a highly soft and porous hydrogel. A stress applied on the soft hydrogel surface deforms it and forces the absorbed solvent to move by flowing through the network of pores. This coupled phenomenon sets the framework of poroelasticity. Moreover, polymeric gels are often used in ultra-thin coatings to tune surface properties. Together with the characteristic poroelastic coupling, this thinness challenges the modelling of their response. In this article, we derive the point-force mechanical response of a thin, permeable and poroelastic layer bounded to a rigid substrate. We show that the gel surface is only deformed around the indentation point, within a radius on the order of the layer thickness. The obtained Green's function can be directly used to predict the space- and time-dependent surface deformation of the gel. Our findings are relevant for a broad range of applications, such as indentation experiments on swollen gels, thin membranes or soft and living systems, as well as lubrication problems involving a soft and porous wall, for instance in microfluidics.

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cond-mat.soft 2026-04-30

Category theory turns biological hierarchies into engineered actuators

A Category-Theoretic Framework from Biological Mechanics to Engineered Stimulus-Response Systems

A structure-preserving functor maps pinecone mechanics to four actuator classes realized in parametric scripts and physical tests.

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Natural materials achieve adaptive behavior through hierarchical organization and coupled mechanisms across scales. Their translation into engineering, however, remains largely heuristic. What is missing is a formal translation framework that carries biological design logic into engineered realization while preserving physical consistency across levels of abstraction. Here we present a category theoretic compositional framework for verified nature-derived design. The framework defines a category of stimulus response dynamical systems with natural and artificial subcategories. It introduces a structure preserving implementation functor from biological mechanics to engineered systems. It also formalizes a machine agnostic specification layer that links behavioral intent to executable fabrication programs. We instantiate the framework on the hygromorphic pinecone hierarchy as a representative biological case. We implement the full pipeline in Grasshopper, where formal specifications are translated into modular parametric scripts that preserve the compositional structure of the model. The resulting designs are fabricated by fused filament fabrication, evaluated experimentally, and tested against model predictions derived from the pipeline. The current implementation generates four actuator classes spanning two stimulus types and two kinematic responses. One actuator arises purely through composition from previously validated components, without additional manual derivation. The results show that compositionality can function not just as a descriptive language, but as a generative and system level verifiable method for mechanical material design. More broadly, the work provides a concrete route for embedding formal multiscale reasoning within increasingly computational, generative, and physics-driven design workflows.

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cond-mat.soft 2026-04-30

Generalized phase rule limits coexisting patterns in active mixtures

Coexistence of patterned phases in chemically active multicomponent mixtures

A Lyapunov functional whose minimization shows complex patterns form modularly from independent phases.

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Chemically active mixtures exhibit complex patterns that emerge from the interplay of physical interactions and reactions among components. Individually, these two processes are well-understood: Physical interactions can give rise to phase separation, whereas reactions can form reaction-diffusion patterns. To understand the combination of both processes, we identify a Lyapunov functional for a class of chemical reactions. By minimizing this functional, we identify a generalized Gibbs phase rule that governs the number of coexisting patterns, and we demonstrate that complex patterns can be created by the modular combination of independent phases. Our theory unveils complex stationary patterns in chemically active mixtures and provides a framework for analyzing more complex systems.

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cond-mat.soft 2026-04-30

Constant volume cuts solidification driving force for low-density solids

A Thermodynamic Analysis of Enhanced Metastability in Isochoric Supercooled Liquids

Helmholtz free-energy bias is smaller than Gibbs under isochoric constraint, exponentially lowering nucleation rates when solids expand on 4

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Experiments show that isochoric (constant-volume) conditions enhance supercooling stability relative to isobaric (constant-pressure) conditions. Here, combining Helmholtz equilibrium thermodynamics with a first-order perturbation methodology, we derive an inequality governing nucleation stability under volumetric constraint. The derivation provides a general thermodynamic proof that for any substance undergoing phase transformation in which the solid is less dense than the liquid, the Helmholtz driving force for solidification in isochoric systems is smaller than the Gibbs driving force in isobaric systems. Since nucleation rates depend exponentially on the inverse square of the driving force, this provides a thermodynamic basis for the observed suppression of nucleation rates. While a full stochastic treatment is beyond the scope of this work, the reduction in driving force implies a weakening of the bias toward growth of pre-critical fluctuations, increasing their probability of thermal dissolution. The analysis yields a dimensionless isochoric stability number. This number is computable from bulk thermodynamic data alone and provides a geometry-independent criterion for comparing metastable liquid stability across materials and conditions.

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