Optical Characteristics of Stretchable Chiral Photonic Film based on Chiral Liquid Crystals via in situ Photopolymerization

Abstract

Chiral liquid crystals (CLCs) spontaneously form a supramolecular helical structure due to the helicoidal molecular rotations. This helical structure of CLC provides a periodic variation of dielectric tensor and results in electromagnetic light propagation forbidden band so-called photonic band gaps (PBGs) [1]. Similar to other LC phase materials, CLC shows stimulus responsive behaviours against various external stress including light, temperature, electric field, and mechanical strain. Thanks to the self-organizing feature of photonic band structures as well as, the band tunability by various external stimuli, CLCs have attracted considerable interest in diverse applications, such as sensors [2], laser devices [3], and reflective displays [4]. Especially, the PBG tuning by mechanical deformation is of interest for sensing or micro-actuating applications with great potential. Among several fabrication methods for mechanochromic CLC gels, including anisotropic deswelling or inducing biaxial stress method, in situ photopolymerization grants us highly aligned samples with qualitative optical performance and a simple fabrication process. In this study, we demonstrate the fabrication procedure and optical characteristics by a mechanical strain of free-standing CLC film via in situ photopolymerization (Fig.1).