Adsorption Kinetics and Adsorption Isotherm of Poly(N-isopropylacrylamide) on Gold Surfaces Studied Using QCM-D

The adsorption kinetics and the adsorption isotherm of poly(N-isopropylacrylamide) (PNIPAM), in its stretching state, on a gold surface have been studied using a quartz crystal microbalance with dissipation monitoring (QCM-D). The adsorption process exhibits an exponential behavior following a concentration change in the solution; the decay constant (reciprocal time constant) of the adsorption shows a linear relationship with concentration, from which the adsorption and desorption rates of the molecule on the gold surface have been determined. The equilibrium coverage of the adsorbed PNIPAM rises sharply at low concentration and approaches a plateau as the concentration reaches 20 ppm in weight. The plateau is interpreted as monolayer completion of PNIPAM. The dissipation factor increases with concentration at low coverage and shows a slight decrease as the monolayer completion of PNIPAM is approached.