Disjoining Pressure and Swelling Dynamics of Thin Adsorbed Polymer Films under Controlled Hydration Conditions

Abstract

In this paper we study the static properties and the dynamical swelling behavior of thin spin-coated layers of natural polysaccharides on Si/SiO2 substrates: the neutral and slightly branched dextran and the negatively charged, linear hyaluronic acid, by ellipsometric observation of the film swelling in a humidity-controlled environmental chamber. Equilibrium swelling ratios and disjoining pressures are measured as a function of the relative humidity of the surrounding atmosphere, which was varied from 4% up to 98%, with the former corresponding to intermolecular separation distances smaller than 6 A. With increasing water uptake the disjoining pressure curves exhibit a crossover from hard-core repulsion to a regime dominated by hydration forces, which were recently recognized to dominate the interaction of polysaccharides at close distances. On the basis of the static measurements, the kinetics of swelling of the adsorbed polymers were determined by a sudden application of an osmotic stress. The kinetic...