Effect of supercritical carbon dioxide on nanoporous polyhexafluoropropylene

The effect of supercritical CO₂ (sc-CO₂) on the size distribution of free volume holes (nanopores) in a polyhexafluoropropylene (PHFP) polymer matrix has been studied. Residual (after CO₂ release) swelling improves gas transport properties of the material. Relaxation of these properties over time has been compared with changes in permeability and nanoporosity. For PHFP samples with different histories, the data on nanoporosity have been obtained using positron annihilation lifetime spectroscopy (micropores) and the lowtemperature gas sorption technique (mesopores and part of micropores). Matching of the data is intended to reveal the role of pores of different sizes in permeability of membrane materials to different gases and determine the specifics of application of the positron annihilation technique to studying sc-CO₂-modified objects.