Thiol-Acrylate Main-Chain Liquid-Crystalline Elastomers with Tunable Thermomechanical Properties and Actuation Strain

The purpose of this study was to investigate the influence of cross-linking on the thermomechanical behavior of liquid-crystalline elastomers (LCEs). Main-chain LCE networks were synthesized via a thiol-acrylate Michael addition reaction. The robust nature of this reaction allowed for tailoring of the behavior of the LCEs by varying the concentration and functionality of the cross-linker. The isotropic rubbery modulus, glass transition temperature, and strain-to-failure showed strong dependence on cross-linker concentration and ranged from 0.9 MPa, 3 degrees C, and 105% to 3.2 MPa, 25 degrees C, and 853%, respectively. The isotropic transition temperature (T-i) was shown to be influenced by the functionality of the cross-linker, ranging from 70 degrees C to 80 degrees C for tri- and tetra-functional cross-linkers. The magnitude of actuation can be tailored by controlling the amount of cross-linker and applied stress. Actuation increased with increased applied stress and decreased with greater amounts of cross-linking. The maximum strain actuation achieved was 296% under 100 kPa of bias stress, which resulted in work capacity of 296 kJ/m(3) for the lowest cross-linked networks. Overall, the experimental results provide a fundamental insight linking thermomechanical properties and actuation to a homogenous polydomain nematic LCE networks with order parameters of 0.80 when stretched. (C) 2016 Wiley Periodicals, Inc.