Poly(N-isoproylacrylamide) (PNIPAM) has a lower critical solution temperature (LCST) at ~32 �C. PNIPAM undergoes coil-to-globule transition across the LCST. Experimentally, one observes a hysteresis associated with the transition from coil-to-globule and globule-to-coil conformations. The atomistic details of the origin of hysteresis and the effect of heating rate on the hysteresis shown by the PNIPAM is not yet understood. In this study, molecular dynamics (MD) simulations of a fully atomistic level model of PNIPAM-water system is used to understand the origin of hysteresis associated with the globule-to-coil transition. Heating and cooling cycles in the temperature range of 278 to 315 K were carried out with equilibration time of 2 and 5 ns, respectively. Simulation trajectories were analyzed to study structural and dynamical properties of PNIPAM and water. Analysis of the simulation trajectories, carried out at two different heating rates, suggests that the extent of hysteresis is strongly correlated with the heating and cooling rate.

Effect of heating rate on the hysteresis in coil-to-globule transition in single poly(N-isopropylacrylamide) chains solvated in water: A molecular dynamics study

243rd National Meeting (2012)

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