Novel polyacrylamide hydrogels by highly conductive, water-processable graphene

Three-dimensional polymeric hydrogels are usually brittle and insulating in nature, which sets limitations to high-end applications. It remains a great challenge to develop electrically conductive and mechanically strong hydrogels. We developed polyacrylamide (PAM) composite hydrogels, by using electrically conductive yet processable graphene sheets and employing in situ free radical polymerization of acrylamide in the aqueous suspension of graphene sheets. Cost-effective graphene sheets were prepared via the simultaneous oxidation and sonication of commercial graphite, which could make the sheets compatible with hydrogel matrices. The sheets proved to reach a percolation threshold of electrical conductivity at 0.8 vol% graphene in the hydrogel matrix; at 1.0 vol% Young's modulus and compressive strength were found to respective increase by 255% and 2000%. Graphene sheets were observed to uniformly disperse in the matrix and they had hydrogen bonding with PAM, both of which contributed to the improvements. The hydrogels hold many potential applications. (C) 2016 Elsevier Ltd. All rights reserved.