(551f) Cholesteric Blue Phase Liquid Crystal Core-Shells

A high level of chirality gives rise to a 3D assembly of anisotropic molecules into double-twisted cylinders (DTC). The arrays of DTCs and networks of line defects can later pack into cubic lattice symmetries and form the so-called cholesteric blue phases (BPs). BPs exhibit distinct optical features thanks to the inherent coupling of crystallinity and fluidity, which have a multitude of practical implementations, such as tunable photonic band-gaps materials, waveguides, and variable iris. The majority of these applications rely on confining cholesteric BPs in meso- or sub-micro correlated lengths to control and manipulate the visible light direction. Accordingly, geometrical confinement introduces additional frustration to BP molecular orientations leading to the emergence of exotic molecular organizations and morphologies which does not generate in bulk (unconfined) state and consequently affecting their optical properties.

In this research work, We demonstrate the effect of geometrical frustration on molecular configuration, domain morphologies, and phase behavior of the cholesteric BPs in shell geometries as function of shell thickness and boundary condition. The morphologies of BPs confined in shell geometries significantly affected by surface anchoring conditions in which the homeotropic induced anchoring alters BPI domain alignments resulting in 30 nm blue-shift in the reflected color. Moreover, BP confined in shells exhibit the new phase behavior upon reducing the shell thickness. Our experimental observations are accompanied by computational simulations to obtain more insights into the underlying physics of the new orientational principles.