Carbon Dioxide Sorption and Plasticization of Thin Glassy Polymer Films Tracked by Optical Methods

Abstract

Our previous publications have demonstrated that thin glassy polymer films respond to highly sorbing penetrants, such as CO2, quite differently than thick films. These studies focused on CO2 permeation behavior and revealed that, for thin films, CO2 permeability at constant CO2 pressure goes through a maximum followed by a continual decrease in permeability owing to physical aging. So far, thick and thin glassy polymer films have been compared in the context of permeability, but lack of substantial means of obtaining thin film sorption data has prevented adequate comparison of thick and thin films in the context of gas solubility. In this paper, spectroscopic ellipsometry is used to obtain simultaneously the film thickness and CO2 sorption capacity for thin glassy polymer films. This allows a more comprehensive look at CO2 permeability, sorption, and diffusivity as a function of both CO2 pressure and exposure time. The evidence reported here suggests that thin film sorption behavior is substantially diffe...