Mechanochromic Responses of Cholesteric Liquid Crystal Droplets with Nanoscale Periodic Helical Structures Showing Reversible and Tunable Structural Color

Abstract

Cholesteric liquid crystal (CLC) droplets with nanoscale periodic helical structures are omnidirectional under planar anchoring, and light is selectively reflected from the droplet center at all directions. However, when CLC droplets are too small, random light scattering dominates. In this regard, we present a facile method to increase the selective Bragg reflection of CLC droplets and demonstrate the unique mechanochromic responses of CLC-droplet-dispersed polymer films. The films are originally opaque and white, when the films are bidirectionally stretched, spherical CLC droplets are squeezed into oblate shape and the point defect at the center of each CLC droplet transitions to a ring defect, greatly increasing the selective Bragg reflection region and resulting in the appearance of structural color. By tuning the helical pitches via the chiral dopant concentration from 1.7 to 3.0 wt %, the desired structural color is achieved. Smart sensors show color changes in response to hydration and dehydration are designed, paving the way for the developments of CLC-based functional materials and smart devices.