Physical Properties of Anisotropically Swelling Hydrogen-Bonded Liquid Crystal Polymer Actuators

Glassy polymeric actuators are described which reversibly deform in response to changes in pH and/or the presence of water. Hydrogen-bonded liquid crystalline monomers act as precursors, and these materials are photopolymerized (without mechanical drawing) into monodomain nematic networks. We discuss the influence of film composition, polymerization conditions, and chemical treatments on the properties of these anisotropic networks. We show that large-amplitude reversible motion can be generated in response to small changes in pH. Pretreatment in basic solutions also activates a response to water, and this effect is investigated in detail. Elastic moduli, which are directly related to the generation of work, have not been reported previously, and therefore particular attention is given to mechanical properties. A marked anisotropy is observed in the moduli parallel and perpendicular to the nematic director. We find that pretreatment in basic solutions reduces this anisotropy yet preserves magnitudes on the order of 2 GPa. Employing complex director profiles (such as the twisted configuration), extremely large amplitude bending-mode deformations are induced in response to small pH changes, immersion in water, or variations in the relative humidity. Since the elastic moduli are large, work output significantly greater than conventional liquid crystal elastomers is predicted