Photoresponsive Coatings by Light-Driven Molecular Motors in Cholesteric Liquid Crystal Microcapsules

Photoresponsive coatings that can change their color in response to light at ambient temperature have large potential applications. Cholesteric liquid crystals (CLCs) are promising photochromic materials, as they are known to reflect light selectively and their optical properties can be modulated with a wide range. However, it remains a major challenge to fabricate photoresponsive coatings that combine fast and good responsivity, fabrication feasibility, and mechanical strength and, more importantly, that can be applied at a large area with excellent stability. In this study, Pickering emulsions containing CLC microdroplets doped with light-driven molecular motors as photoresponsive chiral dopants were prepared via cellulose nanocrystals (CNCs) which serve as both Pickering emulsifiers and alignment agents of CLCs. A melamine-formaldehyde (MF) resin hybrid shell was fabricated via in situ polymerization to form thermally stable CLC microcapsules. These microcapsules were mixed with curable binders, resulting in photoresponsive coatings. The photochromic material which features highly selective addressability of the reflective light wavelength in the visible light region, good reversibility, and viewing angle independence was painted in a large area on both hard and soft substrates, providing a versatile platform for enhanced encryption and smart coatings.