Adaptation of evapoporometry (EP) to characterize the continuous pores and interpore connectivity in polymeric membranes

Abstract

Evapoporometry (EP) determines the pore-size distribution (PSD) based on the Kelvin equation that relates the evaporation rate of a volatile wetting liquid to the pore diameter. EP offers several advantages relative to other PSD characterization methods. EP is adapted here to characterize only the continuous pores rather than all the pores. This adaptation involves sequentially injecting a volatile wetting liquid under the membrane followed by a denser, non-volatile, non-wetting liquid to seal the pores as the overlying volatile liquid evaporates. EP characterization of only the continuous pores shifts the PSD based on all the pores towards smaller pores as indicated by a decrease in the average pore diameter from 15.2 nm to 13.2 nm for a 500 kDa PVDF membrane and from 12.8 nm to 11.7 nm for a 300 kDa PES membrane. The difference between the total pore mass for the two EP characterization protocols was 46.2% and 36.3% for the PVDF and PES, respectively. This provides an assessment of the interconnectivity of the pores, which was quite high as would be expected for these two solvent-cast membranes. By injecting an underlying, non-volatile, non-wetting liquid, EP can be adapted to use non-wetting volatile liquids of interest in some applications.