Effect of thermal modification on swelling dynamics of ultrathin polymer films

Abstract

Abstract Swelling dynamics of spin coated ultrathin polyacrylamide films, annealed at the onset of thermal degradation temperature (220 °C) of polyacrylamide have been studied using in situ X-ray reflectivity technique to understand the effects of thermal modification of the polymer to their swelling dynamics. The results are compared with those of thermally annealed unmodified films from our previous study. Significant changes in swelling dynamics and swellability of the modified films are observed. The swellability of the modified films was greatly reduced compared to the annealed ones. The swelling dynamics of the films are analyzed with a model where the dynamical behavior for the swelling was expressed in terms of combination of two independent components namely “free” and “restricted”. Analyzes of the results show that the effect of thermal modification can be clearly observed in the free component whereas it was not distinguishable for the dynamics of attached component. The study of mass uptake behavior of solvent molecules shows that this process was dependent on film thickness and was non-Fickian in nature. Comparison of the diffusion coefficients of water to that of the free component of the polymer chains shows that for thinner films swelling was controlled by the solvent uptake whereas for the thicker ones the two processes are independent.