Molecular dynamics studies of poly(N-isopropylacrylamide) endgrafted on the surfaces of model slab pores

We report first results of a systematic study of the properties of thermo-responsive polymer chains of poly(N-isopropylacrylamide) (PNIPAM), which are endgrafted onto the inner surfaces of a slab pore of approximately 9 nm width. We have systematically varied the strength of the PNIPAM-surface interaction energy to estimate the variation of the extent of the thermo-responsive effect on different surfaces. For weak to intermediate PNIPAM-surface interactions, the MD simulations show thermo-responsive behavior as characteristic changes of the radius of gyration and other measures of the polymer structure and polymer-water interactions, when comparing simulations below (at 280 K) and above (at 320 K) the lower critical solution temperature of PNIPAM, which is at 305 K. When the PNIPAM-surface interactions become stronger, the polymer loses its thermo-responsive behavior and is adsorbed flatly on the pore walls at both investigated temperatures.