Design of Hemispherical Surface Micropattern via Liquid Crystal Droplet Array

Immobilized microdroplets composed of liquid crystals (LCs) exhibit high birefringence and rapid response to external stimuli, making them ideal for optical and sensory applications. However, a major challenge still remains: controlling their size and local distribution while retaining high throughput. In this work, we simply but precisely manipulate the hemispherical LC microdroplet array on a substrate through controlled nucleation and growth. Specifically, we controlled both diffusion and phase separation of LCs within the polymer matrix upon heating and cooling sequences, respectively. Exact size and number density were achieved precisely by varying two representative temperature profiles, maximum heating temperature and cooling rate. The LC droplet arrays possess scattered structural color which arises from the matching of dispersion wavelength between polymer matrix and specific size of LC droplets. Moreover, the locally UV-irradiated region induces wettability differences on the substrate, which produces multi- or binary-colored optical images only under a predesigned temperature profile. This enables the design of a security platform that can only be decrypted using a unique physical key.