Study on the Optical and Mesomorphic Properties of Cholesteric Side-Chain Liquid Crystalline Elastomers Containing a Nematic Cross-Linking Agent

Abstract

To study the effect of the content of the nematic cross-linking units on the mesophase behaviors, the optical and mesomorphic properties of liquid crystalline elastomers (LCEs), a series of LCEs have been synthesized by hydrosilylation reaction with poly (methylhydrogeno)siloxane, a cholesteric liquid crystalline monomer, and a nematic crosslinking agent. The chemical structures and properties of the synthesized LCEs have been investigated by use of various techniques. Homopolymer P 0 bearing only cholesteric component displays a smectic A phase, but elastomers P 1 -P 5 containing different content of Color versions of one or more of the figures in the article can be found online at www.tandfonline.com/lpte. 661 nematic cross-linking units show a cholesteric mesophase. The reflection wavelengths of the LCEs show a weak temperature dependence at lower temperatures but a strong temperature dependence at higher temperatures. Furthermore, the maximum reflection wavelengths of the LCEs can be stabilized over a wide temperature range when the LCEs are heated, suggesting that the helical structure and pitch of the cholesteric phase can be stabilized with a polymer network. INTRODUCTIONLCEs represent the model of fascinating soft matter materials, combining entropy elasticity and the mechanical characteristics of elastomers with the orientational order and anisotropic properties of liquid crystals [-5] . Recently, LCEs have attracted both industrial and theoretical interests due to their remarkable properties, such as mechanical, thermal, electrical, and optical properties [7][8][9][10][11] . The lightly cross-linked network structures of LCEs can be obtained by copolymerization of different LC mesogens with various cross-linking agents. The different LC mesogens and cross-linking segments in LCE systems can result in materials with a variety of mesophases and distinct properties [12][13][14][15] , which make them promising for applications in actuators, photonics, and shape-memory materials [16][17][18][19][20][21] .Among the various mesophases of LCEs, the study of cholesteric LCEs is one of the most important and complex topics due to their special piezoelectricity, tunable mirrorless lasing, and photonics besides conventional properties of the cholesteric mesophase [22][23][24][25][26][27][28] . Correspondingly, they have the potential to act as nonlinear optical materials, electro-optical materials and the novel piezoelectric device. In recent years, more and more research interests have been focused on the helical structure and regulating the pitch of the cholesteric mesophase because of their unique properties that stem from the periodic helical supramolecular structure characterized by handedness architecture and helical pitch. The helical structure and the pitch depend on temperature and the concentration of different constituents, which is very useful for practical applications in optical devices including light modulators, refractive displays, and temperature sensors [29][30][31][32][33] . Meanwhile, the pitc...