(574b) Azobenzene Containing Main-Chain Liquid Crystalline Elastomer for Fully Reversible Photo- and Thermal Actuation

A series of main-chain liquid crystalline elastomers (LCE) containing novel azobenzene mesogens, containing two, three, four phenyl rings respectively, were synthesized via hydrosilyzation addition reaction under ambient condition.  Their structures and properties of the elastomer films were studied in detail by a combination of nuclear magnetic resonance (NMR), differential scanning calorimetry (DSC), polarized optical microscopy (POM), RSA solid dynamic mechanical analyzer and in-situ two-dimensional X-ray scattering. With large uniaxial stretch at elevated temperature, followed by annealing procedure, a very perfect reorientation monodomain Smectic-C liquid crystalline phase was obtained and confirmed by the X-ray diffraction pattern. The prepared monodomain films showed strong opto-mechanical responses upon exposure to ultraviolet (UV) light at 365 nm, as a result of an optically induced isomerization of azobenzene moieties in the backbone. Compared to the previously reported side-chain and copolymer LCEs, the new end-on main-chain LCEs presented much more pronounced mechanical responses due to the large backbone molecular motion during the trans-cis transition of the azobenzene moieties upon UV irradiation. The UV light induced stress responses that obtained with the mesogenic groups reached over 800 kPa, which provide a promising prospect for artificial muscle, actuation and sensor applications.