EXCHANGE KINETICS OF ADSORBED POLYMER AND THE ACHIEVEMENT OF CONFORMATIONAL EQUILIBRIUM

We study adsorption-desorption kinetics of polymer chains at a solid s urface. Protiopolystyrene, adsorbed from dilute cyclohexane to a singl e solid surface of oxidized silicon, was displaced by deuteriopolystyr ene. A single time constant, tau(off), described displacement for a si gnificant time (1-3 h), followed by a period of slower desorption kine tics. An aging effect, in which tau(off) continued to increase even af ter the mass adsorbed had equilibrated, implied surprisingly slow rear rangements of adsorbed chains in the direction of conformational equil ibrium. After long aging times, ranging from hours to days, tau(off) r eached a plateau value. This equilibrated desorption time increased ex ponentially with the length of adsorbed chains.