Blue-phase liquid crystal droplets

Significance Blue phases represent distinct liquid states of matter having a high viscosity, finite shear modulus, and Bragg reflections in the visible spectrum. These properties arise from a highly ordered defect structure, unique amongst complex liquids, which is stable only over a narrow range of temperature. The number and characteristics of the corresponding unit cells could in principle be altered by confinement. In this work we show that the stability of blue phases can be increased by preparing them into small droplets. We demonstrate that defect structure, color, and morphology can be manipulated by controlling droplet size, temperature, and anchoring, thereby offering intriguing opportunities for optical devices based on chiral liquid crystals. Blue phases of liquid crystals represent unique ordered states of matter in which arrays of defects are organized into striking patterns. Most studies of blue phases to date have focused on bulk properties. In this work, we present a systematic study of blue phases confined into spherical droplets. It is found that, in addition to the so-called blue phases I and II, several new morphologies arise under confinement, with a complexity that increases with the chirality of the medium and with a nature that can be altered by surface anchoring. Through a combination of simulations and experiments, it is also found that one can control the wavelength at which blue-phase droplets absorb light by manipulating either their size or the strength of the anchoring, thereby providing a liquid–state analog of nanoparticles, where dimensions are used to control absorbance or emission. The results presented in this work also suggest that there are conditions where confinement increases the range of stability of blue phases, thereby providing intriguing prospects for applications.