Deformable cholesteric liquid crystal microcapsules for high-reflectivity smart coatings

Abstract

The periodic helical structure of cholesteric liquid crystals (CLCs) makes them an ideal material for smart chromogenic coatings. To address their high fluidity and susceptibility to environmental contamination, CLCs are commonly encapsulated in spherical microcapsules. Within these microcapsules, CLCs usually adopt a radial alignment, resulting in a small Bragg reflection spot at the center of the sphere, which contributes to coatings with low reflectivity. Although large microcapsules can enhance the reflectivity, their application is often limited by the intrinsic brittleness of common polymer shells, such as melamine–formaldehyde (MF) resin, making them vulnerable to rupture during the drying process. In this study, we modified MF resin with hydroxy-terminated polydimethylsiloxane (HTPDMS), significantly improving the toughness of the shell and thereby ensuring the structural integrity of large microcapsules during the drying process. Notably, we observed that the microcapsules with toughened shells transition from a spherical to an oblate shape during drying. This deformation increases the area of the central reflection region, leading to a substantial enhancement in overall reflectivity, with the thermochromic coating's reflectivity increasing from 28% to 36%. Furthermore, the modified shell exhibits excellent versatility, enabling the encapsulation of various CLC cores with different response characteristics. This capability provides a promising strategy for creating multi-responsive smart coatings with enhanced reflectivity.