{"id":"eecce833-6aa8-4429-8bf1-d52ed02762a7","arxiv_id":"2608.10851","paper_version":1,"verdict":"CONDITIONAL","confidence":"MODERATE","novelty_score":6.0,"correctness_risk":"medium","formal_verification":"none","parameter_count":0,"one_line_summary":"Maximum spreading of impacting polymer drops is unaffected by elasticity; a new ratio Gamma of elastic to viscous energy remains far below one across all tested impact conditions.","lead":"Experiments with constant-viscosity polymer drops show that elasticity does not change the maximum spreading width of an impacting droplet, despite large Weissenberg and Deborah numbers. The authors add a dimensionless number, Gamma, that compares stored elastic energy with viscous dissipation and predicts when elastic resistance should appear.","discovery_kind":"new_method","skeptic_critique":{"model":"deepseek-v4-flash","headline":"The identical-spreading claim rests on a self-cited Newtonian baseline (Eq. 3) whose derivation and dataset are absent; an inaccurate baseline could hide elastic deviations within the quoted 10% scatter.","rationale":"The paper's central assertion is a null result: polymer elasticity does not change D_max. The evidence is a data collapse onto Eq. 3 with Gamma=0, a curve inherited from the authors' prior arXiv paper (ref. 4). The load-bearing step is therefore the accuracy of that Newtonian baseline over the full experimental range. The main text defers the derivation of Eq. 3, the V approx sqrt(E) closure, and the Gamma formula to a Supplement that is not part of the preprint; the data link is a placeholder. I checked the viscous limit: using Oh = We^(1/2)/Re, Eq. 3 reduces to beta proportional to Re^(1/5), consistent with classical scaling, so there is no obvious internal contradiction. But an unknown coefficient or interpolation error of order 10% cannot be excluded without the derivation or data. The 'quasi-Boger' category also raises the concern that shear thinning at impact shear rates might offset elastic resistance; the rheological characterization is again only in the missing Supplement. None of this refutes the conclusion, but it makes the conclusion unverifiable from the preprint as posted. The reader's weakest-assumption analysis identifies the same baseline issue, and I agree. The appropriate verdict remains conditional: the paper should be accepted only after the Supplement, dataset, and per-point uncertainties are released, and ideally after a direct comparison with an independent Newtonian baseline.","tokens_in":8465,"tokens_out":21844,"duration_ms":216753,"concrete_test":"Request the dataset and Supplement from the authors. Recompute the normalized spreading beta_max/sqrt(We E) for every polymer point against an independent Newtonian baseline (e.g., the universal rescaling of Lee et al. 2016 or Laan et al. 2014) instead of Eq. 3. If any Boger or quasi-Boger point deviates by more than 10% from this independent baseline while falling within 10% of Eq. 3, the identical-spreading conclusion is an artifact of the self-cited baseline. Also verify in the Supplement's rheometry that the Boger-fluid viscosity stays within 5% of mu_0 up to the largest impact shear rate (gamma_dot_s = (3 V_0 / 2 D_0) V beta_max^2); if viscosity drops by more than 10%, shear thinning could cancel elastic resistance.","verdict_should_be":"UNCHANGED","load_bearing_attack":"The central null result is established by comparing Boger-fluid spreading to the Newtonian master curve beta_max(Gamma=0) from Eq. 3, which is taken from the authors' own prior model (ref. 4). The derivation of Eq. 3, including the kinematic closure D_max = t_s V_s, the average-velocity closure V approx sqrt(E), and the harmonic-mean interpolation, is relegated to a Supplementary Material that is not included in the preprint, and the dataset link is the placeholder 'XXX'. If the baseline is inaccurate for the tested range (We 155-763, Re 18-11,500), the claimed collapse in Fig. 2b could be an artifact of the chosen normalization, and elastic effects of order 10% (the quoted experimental scatter) could be hidden. In addition, the decoupling from shear thinning assumes the Boger fluids are constant-viscosity at impact shear rates much greater than 1000 s^-1; the rheological evidence supporting mu_i = mu_0 is only in the same missing Supplement. Without these materials, the comparison cannot be independently checked.","agreement_with_reader":"agree"},"referee_report":{"model":"deepseek-v4-flash","summary":"The paper reports an experimental study of the maximum spreading ratio of viscoelastic drops, using Boger fluids (PEO and PAAM in Newtonian solvents) to decouple elasticity from shear-thinning over a wide parameter range (We = 155–763, Re = 18–11,500, Oh = 0.002–1). The authors derive a dimensionless elasto-viscocapillary energy balance, introduce the ratio Gamma of elastic to viscous energy (Eq. 2), and show that Gamma < 1 for all tested conditions, concluding that elasticity is energetically negligible during spreading and that the maximum spreading ratio is identical to the Newtonian prediction, contrary to the expectations from Wi and De. The central evidence is the collapse of experimental data onto a Newtonian master curve in Fig. 2b, together with the theoretical sensitivity analysis in Fig. 3a.","tokens_in":8622,"tokens_out":6783,"duration_ms":68984,"significance":"If the central claim holds, the paper resolves a long-standing paradox by showing that polymer elasticity does not resist the expansion phase of drop impact, so maximum spreading remains governed by inertia, capillarity, and viscous dissipation alone. The study has clear strengths: the use of constant-viscosity Boger fluids is the right experimental strategy to separate elasticity from shear thinning; the parameter range is broad; the Hertzian-model choice is explicitly framed as a conservative upper bound; and the Gamma criterion is a parameter-free, falsifiable prediction rather than a fit to the observed spreading data. However, the verification is currently incomplete: the derivation of Eq. (3), the rheological characterization, and the dataset are all deferred to a Supplementary Material that is not included, and the Newtonian baseline is taken from the authors' own prior model. These gaps are significant because the null result is defined as a collapse onto that baseline.","major_comments":[{"comment":"The central comparison in Fig. 2b rests on Eq. (3), but the derivation of Eq. (3)—including the kinematic closure Dmax = ts Vs, the average-velocity closure V ≈ sqrt(E), and the harmonic-mean interpolation—is stated to be in the Supplementary Material, which is not included in this preprint. The data-availability link is also the placeholder \"XXX\". Without the derivation and the dataset, the claimed collapse onto the Newtonian master curve cannot be independently checked. Please provide the full derivation and make the data available at a permanent repository before the central claim can be assessed.","section":"Eq. (3) and Fig. 2b"},{"comment":"Eq. (3) with Γ = 0 recovers the Newtonian baseline βmax(Γ = 0) of ref. [4], which is the authors' own prior model; neither the derivation nor the raw dataset of that baseline is shown here. The statement that \"this collapse further validates the Newtonian baseline in [4]\" uses the same comparison that is supposed to establish the null result. If the baseline is inaccurate for the tested range, elasticity-induced deviations of order the quoted 10% scatter could be hidden. Please provide an independent validation of the baseline, for example Newtonian solvent data measured with the same setup, or the complete baseline dataset of ref. [4].","section":"Newtonian baseline, ref. [4]"},{"comment":"The decoupling from shear thinning assumes µi = µ0 for the Boger and quasi-Boger fluids at impact shear rates much greater than 1000 s^-1. The rheological evidence for constant viscosity in this range is said to be in the Supplementary Material, which is absent. If these fluids shear-thin at impact rates, enhanced spreading from thinning could offset elastic resistance and mimic the null result. Please provide high-shear rheometry for all fluids, or an explicit estimate of µi at the characteristic impact shear rate γdot_s defined in the text.","section":"Boger-fluid characterization, near Eq. (2)"},{"comment":"The detectability argument in Fig. 3a defines the observable elastic regime as deviations exceeding approximately 10% scatter, and the text states that the ratio of experimental to theoretical spreading yields an average deviation below 10%. However, no error analysis, per-condition statistics, or table of βmax values is presented in the manuscript. Since the 10% noise floor is a load-bearing threshold for the conclusion that Γ ≪ 1 produces no observable effect, please report the actual deviations and their uncertainties.","section":"Fig. 3a and experimental scatter"}],"minor_comments":[{"comment":"The word \"captublack\" in the Fig. 1 caption should be \"captured\".","section":"Fig. 1 caption"},{"comment":"The data availability statement contains the placeholder \"link XXX\"; a working permanent repository link is needed.","section":"Data Availability"},{"comment":"There are missing spaces in phrases such as \"diffusionandadsorptiontimescalesaresignificantly\"; please correct the line-breaking artifacts throughout.","section":"Main text, first paragraph of Section 2"},{"comment":"The axis label \"Eq. [4]\" is ambiguous; it should refer to Eq. (3) of this paper or explicitly to the reference, not to a citation number.","section":"Fig. 2b axis label"},{"comment":"The term \"quasi-Boger fluids\" is used in Fig. 2b and Fig. 3 but is not defined in the main text; please provide a definition or a criterion for this category.","section":"Fluid classification"}],"recommendation":"major_revision","confidential_remarks":"The experimental program and the proposed Gamma criterion are potentially important and appear plausible, but the manuscript is not self-contained: the derivation of the central equation, the rheological support for the Boger-fluid assumption, and the dataset are all in a missing Supplementary Material, and the Newtonian baseline is a self-cited prior model. These are fixable within the scope of a revision, so I would not reject, but the authors should be asked to make the derivation and data fully available."},"author_rebuttal":null,"desk_editor":{"model":"deepseek-v4-flash","letter":"Dear colleague,\n\nQuick take: this is a solid experimental paper that makes a believable claim—polymer elasticity doesn't change maximum spreading for Boger fluids up to 1000 ppm—and it backs the claim with a wide parameter range (We 155–763, Re 18–11,500) and a clever decoupling of elasticity from shear thinning. The new thing is the Gamma criterion, the ratio of elastic to viscous energy, with a conservative Hertzian upper bound for the elastic term. That's a good idea: if the strongest plausible elastic scaling (beta^5) is negligible, weaker polymer-model scalings (beta^2) are also negligible. The logic is sound.\n\nThe experimental design deserves credit. Using Boger fluids (constant viscosity, high elasticity) is exactly how to isolate elastic resistance from thinning, and the collapse in Fig. 2b onto the Newtonian master curve is convincing at face value. The paper also honestly flags its own limitations: the full derivation of Eq. 3 and the Gamma evaluation are in a Supplementary Material that is not included, and the data link is a placeholder 'XXX'. That's a real problem for a null result, because the reference baseline comes from the authors' own prior model (ref. 4). If that baseline were inaccurate, elastic deviations at the 10% scatter level could be hidden. The stress-test note raises exactly this, and I think it lands.\n\nThe soft spots are real but proportionate. The derivation of Eq. 3 is not in the manuscript; the harmonic-mean interpolation and the V≈√E closure are stated but not shown. The paper says the details are in the supplement, which is fine for a preprint, but for a claim that rests on a specific baseline, it makes independent checking impossible right now. The experimental scatter is quoted as 'below 10%' without per-point error bars in Fig. 2b. And the comparison to the recent Avni et al. result (ref. 30) is only qualitative; a direct quantitative comparison would strengthen the paper.\n\nNone of this refutes the central argument. The conservative upper-bound reasoning is robust, and the empirical collapse is hard to fake. The paper deserves a serious referee, but the authors need to release the supplement, the dataset, and per-point uncertainties before the claim can be taken as established. I'd accept this for peer review conditionally, and I'd want to see those materials in the revision.\n\nWorth a reading group slot. I'd cite the Gamma criterion and the Boger-fluid data once the dataset is out.\n\nRecommendation: send to review, but insist on the supplementary material and data being made available.\n\nBest,\n[Your name]","headline":"A careful experimental study with a plausible energetic criterion, but the missing supplementary derivation and dataset placeholder make the central collapse impossible to audit.","tokens_in":9206,"tokens_out":2649,"would_cite":true,"duration_ms":25855,"reading_group":"yes","serious_thinker":"yes","would_accept_peer_review":true},"rs_alignment":null,"lean_confirmation":null,"pith_extraction":{"msc":[],"pacs":[],"model":"deepseek-v4-flash","headline":"Polymer elasticity does not change how far an impacting drop spreads, because the elastic energy stored during spreading is negligible compared with viscous dissipation.","keywords":["Drop impact","Viscoelastic drops","Boger fluids","Maximum spreading ratio","Elastic energy criterion","Polymer additives","Shear thinning"],"falsifier":"The predicted elastic regime is currently untested: prepare a constant-viscosity elastic fluid with $\\Gamma \\gtrsim 1$ by the paper's own formula (for example a low-viscosity Boger fluid with $G \\approx 2 \\mu_i V_0 / D_0$), impact it, and measure $\\beta_{\\max}$. The paper predicts a measurable reduction below the Newtonian baseline in that regime; if none appears, the criterion fails.","tokens_in":8252,"feed_emoji":"💧","tokens_out":6983,"duration_ms":64009,"temperature":0.7,"pith_summary":"The paper sets out to resolve why viscoelastic drops spread exactly as far as Newtonian ones even when classical dimensionless numbers ($Wi$ and $De$) predict elastic, solid-like resistance during impact. The authors' answer is that elasticity is energetically irrelevant in the spreading phase: the stored elastic energy is much smaller than the viscous dissipation for all conditions they could reach. They test this with Boger fluids (constant-viscosity, highly elastic PEO and PAAM solutions), which isolate elasticity from shear-thinning, and find the maximum spreading ratio collapses onto the Newtonian master curve up to 1000 ppm. The paper also derives a dimensionless criterion $\\Gamma$ that bounds when elastic resistance could become observable, and argues that shear-thinning, not elasticity, explains the extra spreading of concentrated polymer drops. If correct, this settles the debate in favor of inertia, capillarity, and viscosity controlling maximum spreading, and shows that $Wi$ and $De$ expectations do not apply to this phase of impact.","feed_headline":"Polymer elasticity does not slow droplet spreading","feed_subtitle":"Impact tests on elastic Boger drops match Newtonian spreading; elastic energy is negligible during impact.","key_machinery":"The load-bearing object is the dimensionless elastic-to-viscous damping ratio $\\Gamma$ (Eq. 2), derived from an energy balance in which the impact kinetic energy is split into surface energy, viscous dissipation, and elastic storage. The elastic storage is deliberately overestimated by treating the drop as a Hookean solid in Hertzian contact, giving an elastic term scaling as $G \\beta_{\\max}^5$; any weaker polymer-constitutive model (Neo-Hookean, Oldroyd-B, FENE-P) would give even less resistance. The kinematic closure $D_{\\max} = t_s V_s$ and the leading-order average-velocity closure $V \\approx \\sqrt{E}$ turn the balance into a closed expression $\\beta_{\\max}(\\Gamma)$, with $\\Gamma = \\frac{8}{5\\pi} \\frac{G D_0}{\\mu_i V_0 \\sqrt{E}}$. The paper also introduces the impact Carreau number $Cu_i = \\dot{\\gamma}_s / \\dot{\\gamma}^*_{\\mathrm{rheo}}$ to separate Newtonian-adherent Boger fluids from shear-thinning concentrated solutions.","core_discovery":"The central discovery is that the maximum spreading ratio $\\beta_{\\max} = D_{\\max}/D_0$ of Boger-fluid drops (PEO and PAAM, up to 1000 ppm) is indistinguishable from the Newtonian baseline for the same impact parameters, with deviations below the typical 10% scatter. The authors formulate an energy balance with inertial, capillary, viscous, and elastic terms, and define $\\Gamma$ as the ratio of elastic to viscous energy, $\\Gamma = \\frac{8}{5\\pi} \\frac{G D_0}{\\mu_i V_0 \\sqrt{E}}$. Evaluating $\\Gamma$ with two independent relaxation-time estimates (Zimm lower bound and CaBER upper bound) gives $\\Gamma \\ll 1$ for every impact tested, so the elastic term is too small to shift the spreading. They conclude that Weissenberg and Deborah numbers, while large, do not predict spreading because they compare microscopic polymer relaxation to the deformation rate rather than the macroscopic energy budget. The observed enhanced spreading of concentrated shear-thinning fluids is attributed to viscosity reduction, not elastic resistance, and concentration actually lowers $G/\\mu_i$ and $\\Gamma$.","pith_inferences":["The authors do not test the predicted elastic regime, since all data sit at $\\Gamma \\ll 1$; a deliberate attempt to reach $\\Gamma \\approx 1$ (for instance a low-viscosity solvent with a high-modulus polymer) would provide the sharpest test of the criterion.","The same energy-budget logic could be applied to other rapid deformations where $Wi > 1$ is used to infer elasticity, such as splashing thresholds or atomization, replacing relaxation-time criteria with an elastic-to-viscous energy ratio.","If the Newtonian baseline's kinematic closures fail at the extremes of the tested Weber and Ohnesorge ranges, part of the claimed collapse could be masking an elasticity effect inside the noise; direct measurements of spreading time and average velocity would reveal it."],"forward_implications":["For Boger-fluid drops up to 1000 ppm, the maximum spreading ratio falls on the pure Newtonian master curve within experimental scatter, so adding elasticity without changing viscosity does not alter how far a drop spreads.","The dimensionless criterion $\\Gamma$, not $Wi$ or $De$, sets the detectability of elastic resistance: only when $\\Gamma \\approx 1$ should a measurable (greater than 10%) reduction below the Newtonian baseline appear.","The material threshold for elastic resistance is approximately $G \\approx 2 \\mu_i V_0 / D_0$, which impact conditions do not reach because the viscous stress at impact shear rates overwhelms the polymer network's elastic modulus.","In concentrated polymer drops, the extra spreading comes from shear thinning, not elasticity, and polymer concentration lowers $G/\\mu_i$ and therefore $\\Gamma$, making elastic resistance even less relevant."],"supporting_citations":[{"why":"Supplies the Newtonian energy balance and kinematic closure ($D_{\\max} = t_s V_s$, $V \\approx \\sqrt{E}$) that defines the $\\beta_{\\max}(\\Gamma = 0)$ baseline used for comparison.","marker":"[4]"},{"why":"Reports the original paradox that polymer additives suppress retraction without changing maximum spreading, the phenomenon this paper explains.","marker":"[14]"},{"why":"Shows rebound suppression arises from normal stresses at the moving contact line, motivating the separation of spreading from retraction.","marker":"[16]"},{"why":"Provides the Zimm-model relaxation times and dilute-solution framework used as the lower bound for elastic modulus estimates.","marker":"[13]"},{"why":"Supplies CaBER relaxation-time and dynamic surface tension data, and the concentration dependence of $G/\\mu_0$, used to evaluate $\\Gamma$.","marker":"[21]"},{"why":"Numerical simulations finding elastic energy below 1% of impact energy, used to support the framework's generality beyond PEO and PAAM.","marker":"[31]"},{"why":"Hertzian contact mechanics used to build the conservative upper-bound elastic-energy scaling ($G \\beta_{\\max}^5$).","marker":"[32]"}],"fun_headline_variants":["Elastic drops spread just like Newtonian ones","Polymer stretch doesn't alter droplet spreading","Elastic energy too weak to change drop spread","Droplet spreading ignores polymer elasticity","Elastic drops match Newtonian spreading exactly"],"cache_read_input_tokens":3200,"weakest_assumption_plain":"Everything rests on the Newtonian baseline from the authors' companion model being accurate for the tested conditions; if that baseline is off by more than the experimental scatter, an elasticity-induced change in spreading could be hidden inside the roughly 10% noise.","fun_headline_variants_meta":{"raw":{"variants":["Elastic drops spread just like Newtonian ones","Polymer stretch doesn't alter droplet spreading","Elastic energy too weak to change drop spread","Droplet spreading ignores polymer elasticity","Elastic drops match Newtonian spreading exactly"]},"model":"deepseek-v4-flash","effort":"low","cost_usd":0.000198,"raw_usage":{"total_tokens":1362,"prompt_tokens":932,"completion_tokens":430,"prompt_tokens_details":{"cached_tokens":384},"prompt_cache_hit_tokens":384,"prompt_cache_miss_tokens":548,"completion_tokens_details":{"reasoning_tokens":363}},"tokens_in":548,"tokens_out":430,"duration_ms":4508,"temperature":1.0,"reasoning_tokens":363,"cache_read_input_tokens":384,"cache_creation_input_tokens":0},"cache_creation_input_tokens":0},"created_at":"2026-08-12T15:45:09.520579+00:00","model_set":{"reader":"deepseek-v4-flash"},"falsifier":"The predicted elastic regime is currently untested: prepare a constant-viscosity elastic fluid with $\\Gamma \\gtrsim 1$ by the paper's own formula (for example a low-viscosity Boger fluid with $G \\approx 2 \\mu_i V_0 / D_0$), impact it, and measure $\\beta_{\\max}$. The paper predicts a measurable reduction below the Newtonian baseline in that regime; if none appears, the criterion fails.","supporting_citations":[{"cited_title":"Kinematic Closure of Drop Impact","cited_arxiv_id":"2605.11797","evidence_quote":"Supplies the Newtonian energy balance and kinematic closure ($D_{\\max} = t_s V_s$, $V \\approx \\sqrt{E}$) that defines the $\\beta_{\\max}(\\Gamma = 0)$ baseline used for comparison."},{"cited_title":"Clasen, J","cited_arxiv_id":null,"evidence_quote":"Provides the Zimm-model relaxation times and dilute-solution framework used as the lower bound for elastic modulus estimates."},{"cited_title":"Gaillard, R","cited_arxiv_id":null,"evidence_quote":"Supplies CaBER relaxation-time and dynamic surface tension data, and the concentration dependence of $G/\\mu_0$, used to evaluate $\\Gamma$."},{"cited_title":"Shende, E","cited_arxiv_id":null,"evidence_quote":"Numerical simulations finding elastic energy below 1% of impact energy, used to support the framework's generality beyond PEO and PAAM."}],"review_version":1}