(5dc) Novel Liquid Crystal Networks

The combination of liquid crystals and polymers results in fascinating materials in which the elasticity of polymers is coupled to liquid crystal (LC) order. In this work, we explore a variety of novel LC gels and elastomers and explore their electro-optical response, mechanical actuation, and flexoelectric behavior. Physical gels made by polymer self-assembly in an LC solovent are thermoreversibly crosslinked. These gels can be made sufficiently dilute that they show a fast electro-optical response in the gelled state. Due to the coupling of polymer network elasticity and LC order, the gel exhibits fascinating texture transitions with temperature. Furthermore, dynamic light scattering studies reveal multiple director relaxation modes, in contrast to covalent gels which show a single relaxation mode. Dilute chemically crosslinked gels can be prepared via ?Click? chemistry of a telechelic SGLCP with azide end-groups and a tri-functional alkyne crosslinker. In contrast to the physically crosslinked networks, the electro-optical behavior is fully reversible. Networks swollen in LC solvents have a low-threshold electro-optic response and show changes in size with temperature due to swelling by the LC solvent. Finally, liquid crystal elastomers based on bent-core liquid crystals have the potential for enhanced flexoelectricity, an electro-mechanical phenomenon whereby a macroscopic polarization develops in response to deformations of the liquid crystal alignment. In order to incorporate bent-core liquid crystals into a polymer network, we prepared two different types of reactive bent core LCs with either an alkene or acrylate functionality. Monofunctional bent-core LCs with a reactive alkene group can be used to make aligned nematic elastomers, and these elastomers can either be studied in the bulk or swollen with bent core LC to investigate their flexoelectic behavior. Following a method demonstrated for calamitic LCs, monofunctional bent-core monomers with an acrylate functionality can also be dissolved in a nematic solvent and polymerized in the presence of a crosslinker to make bent-core LC networks and gels. These various studies of different LC networks and gels provide insight into the connection between physical properties and network structure and also reveal the diversity of behavior accessible with different synthetic approaches.