Swelling Dynamics of Ultrathin Polymer Films

Solvent uptake and swelling of ultrathin spin-coated polyacrylamide films in the presence of saturated vapor of water at room temperature was studied using gravimetric and X-ray reflectivity methods. Solvent uptake was observed to be a faster process, compared to swelling, governed by the Fickian dynamics of the diffusion of water molecules into the free volume of the polymer structure. The swelling demonstrates a slower dynamical behavior that can be modeled in terms of the swelling of a free polymer coil in the presence of a good solvent. Unlike interdiffusion of polymer chains at the interfaces, the attractive interaction of the substrate was found to have no influence on the diffusion process in the case of swelling.