Facile fabrication of patternable and large-area elastic liquid crystal polymer films

Cholesteric liquid crystal elastomers (CLCEs) can change structural colour in response to mechanical stimuli, which can be applied as sensors and optical devices. Thus, the facile fabrication of large-area CLCE films is critical but challenging. Herein, a simple procedure for the preparation of CLCE films by adding a chain-transfer agent is reported. When the CLCE films are fixed between two thermoplastic polyurethane (TPU) films, the obtained TPU/CLCE/TPU sandwich films exhibit mechanochromic behaviours. Due to the decrease of the helical pitch of CLCE film upon stretching, the selective Bragg reflection band shifts to short wavelength. Based on this structural colour change, a flower pattern can emerge or vanish upon stretching. Moreover, a two-dimensional tetragonal grating with elasticity is prepared. The TPU/CLCE/TPU films can be facilely fabricated over large area and used as car films.