Tough Liquid Crystal Hydrogels*

Hydrogels are hydrophilic polymer networks swelling in water solutions. They are widely found in biological systems and used in engineering applications. Mechanical enhancement of them are done by modifying the polymer network, while chemical and biological functioning are realized through the water inclusion. These hydrogels are mostly isotropic and therefore has no optical functions. Here we present a new breed of liquid crystalline hydrogels that bears intrinsic molecular anisotropy by incorporating chromonic liquid crystals in the polymer network. They show strong photoelastic effects, temperature dependence of the mesogenic phases, and a remarkable toughness, making them readily applicable as optical strain sensors. The generic approach of fabricating the liquid crystal gels allows us to combine different polymers and chromonic liquid crystals. It also makes it possible to independently tune the mechanical and optical properties by through chemical composition, crosslink density and hydration rate.