Through the Spherical Looking-Glass: Asymmetry Enables Multicolored Internal Reflection in Cholesteric Liquid Crystal Shells

摘要

Spheres of cholesteric liquid crystal generate dynamic patterns due to selectivernreflection from a helical structure subject to continuously curved boundaries.rnSo far the patterns are investigated exclusively as function of reflections at thernsphere exterior. Here it is shown that the cholesteric shells in a microfluidics producedrndouble emulsion enable also a sequence of internal reflections if the shellsrnhave sufficiently thin top and thick bottom. While such asymmetry is promotedrnby buoyancy when the internal droplet has lower density than the liquid crystal,rnthe elasticity of the cholesteric helix prefers a symmetric shell geometry, actingrnagainst gravity. This subtle balance can hide the internal reflections for longrntime. Eventually, however, the asymmetry is established, revealing a new class ofrnphotonicrnpatterns characterized by colored sharp concentric rings. With the completernknowledge of the diverse light-reflecting behavior of cholesteric liquid crystalrnshells, and utilizing the tunability of the structure period by, e.g., temperature,rnelectric field, or exposure to various chemical species as well as polymer stabilizationrnfor making the shells long-term stable, they may be developed into remarkablernnew optical elements for photonics, sensing, or security pattern generation.