A Generalizable Approach to Direct the Self‐Assembly of Functional Blue‐Phase Liquid Crystals

Blue phases (BPs) are soft and stimuli‐responsive photonic crystals that are interesting for sensing, display, and lasing applications. Polycrystallinity has, however, limited both the study and applicability of BPs. Continuum simulations, which lack molecule‐specific details, predict that striped chemical patterns, consisting of alternating homeotropic and planar regions, can be used to nucleate single crystals of BPs. Here it is experimentally demonstrated that, independent of the chemistry and complexity of the BP forming material, chemical patterns direct the self‐assembly of BPs; these results indicate that a general, thermodynamics‐based continuum description of BP self‐assembly is adequate for a broad range of materials. When the pattern periodicity equals the BPII unit cell size, single crystals with (100) orientation form for all studied materials. Chemical patterns also promote the growth of BPI crystals with (110) orientation. Importantly, the self‐assembly of a photopolymerizable BP is directed and thermally stable, UV‐polymerized single crystals are prepared. The ability to create arbitrarily large, polymeric photonic single crystals with uniform lattice orientation, may have broad implications for optical applications. Chemically patterned surfaces with alternating homeotropic and planar regions promote the growth of BP single crystals and monocrystals with different chemical composition. Pattern design is based on predictions of continuum simulations. By directing the assembly of different BPs, a colorful range of single crystals and monocrystals is obtained. The blue‐phase structure can be made thermally stable through photopolymerization.