Rheology of Poly(N-isopropylacrylamide)–Clay Nanocomposite Hydrogels

Abstract

We used molecular dynamics simulations and experiments to study the rheology of polymer–clay nanocomposite hydrogels. The molecular dynamics simulations studied the formation of physical cross-linked networks as a function of the clay concentration. Simulations showed that while the local structure changed from isolated polymer–clay clusters to a percolating network with increasing clay concentration the networks were only able to sustain stress at concentrations of roughly 1.5 times the percolation transition. Experiments using poly(N-isopropylacrylamide) (PNIPA)–clay nanocomposites at different clay concentrations were compared with simulation results. Experiments showed a transition from viscous to gel like behavior at a clay concentration of 15.24g/L, in good agreement with simulations. The modulus, G′ and G″, prior to yield was observed to increase exponentially with clay concentration and G′ at yield could be fitted to the modified Mooney’s equation.