The diffusivity and solubility of a pure gas in a polymer film are usually measured with barometry, gravimetry or permeation tests. In the case of mixed gases additional optical techniques are required. Swelling, plasticization or even partial crystallization of an amorphous polymer could be induced by the sorption of gases and vapours at specific thermodynamic conditions. These structural modifications are normally measured with independent experiments based on separate optical techniques.

We propose a new method coupling in situ FTIR Spectroscopy in the transmission mode and barometry to investigate simultaneously gas diffusion in polymers and the sorption induced structural modifications [1,2]. Pure and mixed gases in rubbery, glassy and semicrystalline polymers can be studied. We first investigate the sorption of pure CO₂ in Polydimethylsiloxane (PDMS) at 35°C up to 9 bar and of pure CO₂, C₂H₆ and C₃H₈ in Poly(2,6-dimethyl-1,4-phenylene) oxide (PPO) films at ambient temperature and 35°C up to 1 bar approximately. Structural modifications of the matrix are evaluated by analysing the polymer IR spectrum. The solubility of each pure gas in the polymer is quantified with Barometry. Then, after calibrating the IR peaks of each absorbed species in the gas and the polymer phases, the solubility of binary gas mixtures is investigated. Diffusion experiments of gas pairs constituted of CO2 and either methane, ethane or propane in amorphous and semicrystalline PPO are presented. The concentration of each absorbed species is measured directly in the polymer phase by analysing the corresponding IR signal [3]. The partial pressure of each component is measured at sorption equilibrium coupling the IR and pressure measurements. The advantages of the reported technique make it a promising tool for the investigation of transport and mechanical properties of polymeric films.

[1] V. Loianno et al.; Ind. Eng. Chem. Res. 2021, 60, 5494−5503

[2] V. Loianno et al.; J. Mem. Sci. 2022, 652, 120445