Effect of polyacrylamide morphology templated by lyotropic liquid crystal on proton conductivity of acid hydrogels
Acid hydrogels composed of polymer network are promising soft electrolytes whose proton conductivities are most often regulated by acid contents. Herein, promotion of conductivity only by regulating polymer morphology is demonstrated for acid hydrogels with identical acid content. Polymerization of acrylamide at different temperatures in the same aqueous solution, which is a lyotropic liquid crystal (LLC) of 4-(1-ethyldecyl) benzenesulfonic acid (EDBSA) exhibiting a phase transition at 30 ºC, give acid hydrogels composed of ordered and random polymer networks. The ordered polymer network templated by the lamellar liquid crystal at 15 ºC has more interconnected and extended pores than that obtained in the isotropic solution at 45 ºC. Electrochemical characterization shows that the ordered network results in a proton conductivity 48% higher than the random one for the hydrogels holding EDBSA LLC. The higher conductivity is ascribed to more long-range transport pathways formed in larger pores and less barriers of the network for protons to pass through. Enhanced conductivities are also obtained from the ordered polymer network for the hydrogels composed of micellar EDBSA solution and H2SO4 solution but in less degrees. The results shed a light on the dependence of electrochemical performance on polymer morphology of hydrogels and offers a strategy to enhance conductivity of hydrogels without changing the polymer fraction.