(543e) Directed Crystal Nucleation and Growth of Blue Phases By Chemically Patterned Surfaces

Blue phase liquid crystals (BPs) are states of matter that exhibit fluid properties and a configurational structure that produces ordered networks of topological defects. The kinetics of the crystal nucleation and growth processes of such networks are central to the understanding and manipulation of the properties of BPs. In this work, the nucleation and epitaxial growth of BPs are examined with exquisite detail by relying on chemically nano-patterned surfaces to direct their assembly. The use of nano-patterns enables formation of single-crystal BP domains, which grow from BP nuclei that arise when the material is heated up from a cholesteric phase, or when it is cooled down from the isotropic phase. Through a combination of field-theoretic simulations and experiments, it is shown that once a single-crystal BP is formed, the transition into another BP with a different defect network proceeds through a local re-organization of the crystalline structure, which does not require a nucleation stage and exhibits little hysteresis. The transition between single-crystal BPs is shown to be weak first order, with the characteristics of a martensitic-like transformation which is remarkably fast and is the first example of a diffusion-less transformation of this type in soft materials, this opens intriguing possibilities for development of optical devices. From a fundamental perspective, perfectly ordered BPs are shown to offer fertile grounds for the study of directed crystal-nucleation and growth of soft matter.