Rainbows in a bottle: Realizing microoptic effects by polymerizable multiple emulsion particle design

In nature, structural colour generation is based on discriminative light propagation associated with physical structures in the range of the wavelengths of light1. These iridescent structural colours are of immense significance2 but not easy to control experimentally and therefore difficult to exploit for applications. In this work, we employ microfluidics to produce polymerizable double emulsions that can not only induce the already known lensing effect3 but also result in the spectral separation of white light. Here, liquids of varying refractive in-dex that constitute the emulsions resulted in patterns of iridescent colours. After polymerization, the inner emulsion cores collapse and this results in curved concave surfaces on these polymeric microspheres. Interestingly, the light propagation along the curved surfaces undergo total internal reflection, followed by near-field interference along exit structures on the polymerized microspheres4. These structured polymeric particles that are able to generate colour dispersions can be exploited for optical devices, displays and even sensing technologies.