Rheology of Poly(N-isopropylacrylamide)–ClayNanocomposite Hydrogels.

We used molecular dynamics simulationsand experiments to studythe rheology of polymer–clay nanocomposite hydrogels. The moleculardynamics simulations studied the formation of physical cross-linkednetworks as a function of the clay concentration. Simulations showedthat while the local structure changed from isolated polymer–clayclusters to a percolating network with increasing clay concentrationthe networks were only able to sustain stress at concentrations ofroughly 1.5 times the percolation transition. Experiments using poly(N-isopropylacrylamide) (PNIPA)–clay nanocompositesat different clay concentrations were compared with simulation results.Experiments showed a transition from viscous to gel like behaviorat 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 concentrationand G′ at yield could be fitted to the modifiedMooney’s equation. [ABSTRACT FROM AUTHOR]