On the Limits of Sensitivity of PALS to Incorporated Free Volume Holes in Polymeric Membranes and Sorbents: Effect of sc-CO_2 in Polyhexafluoropropelene

摘要

Positron annihilation lifetime spectroscopy (PALS) is a recognized method for the studies of size-distribution of nano-pores (intrinsic free volume holes FVH) in polymers, particularly membrane materials. The limits of this application in the case of "alien" pores, produced on residual swelling of poly(hexafluoro propylene) PHFP by the gas (CO_2) in supercritical (sc-) state are discussed. The obtained conclusions are controlled by measurements of low temperature gas (N_2) sorption (LTGS) and by comparison of the data with the results on permeation of various gases through the PHFP membrane. Attention is payed to relaxation with time of the newly created FVH in the PHFP membrane.