A generic approach to directed self-assembly of polymerizable blue-phase liquid crystals

Blue-phases (BPs) occur in a narrow temperature window between the chiral nematic and the isotropic liquid crystalline phases. They exhibit unit cell sizes of order ~100 nm, making them soft photonic crystals. BPs are promising candidates for displays, sensors, and lasing. Polycrystallinity and thermal instability have still greatly limited their applicability. Chemically patterned surfaces with alternating planar and homeotropic anchoring regions can be used for the epitaxial growth of monocrystalline BPs. We show that such stripe-like patterns direct the self-assembly of BPs with different chemical compositions into single crystals. Experiments together with the support of free energy calculations propose that the strategy of nano-patterned substrates is generally applicable and may serve as a general platform for nucleation and growth of the single-crystalline area with controlled crystal orientation. Each single crystal reflects the light differently which results in the formation of a colorful spectrum. We also demonstrate that the thermal stability of such prepared single crystals can be improved by photopolymerization. Combining the directed self-assembly and the photopolymerization lead to the preparation of thermally stable single crystals of a desire lattice orientation.