Exchange Kinetics of Adsorbed Polymer and the Achievement of Conformational Equilibrium

We study adsorption-desorption kinetics of polymer chains at a solid surface. Protiopolystyrene, adsorbed from dilute cyclohexane to a single solid surface of oxidized silicon, was displaced by deuteriopolystyrene. A single time constant, τ_off, described displacement for a significant time (1-3 h), followed by a period of slower desorption kinetics. An aging effect, in which τ_off continued to increase even after the mass adsorbed had equilibrated, implied surprisingly slow rearrangements of adsorbed chains in the direction of conformational equilibrium. After long aging times, ranging from hours to days, τ_off reached a plateau value. This equilibrated desorption time increased exponentially with the length of adsorbed chains.