Investigation of nanopores in nanofiltration membranes using slow positron beam techniques

The pore distribution of the commercial nanofiltration membranes Desal 5DL, Desal 51HL, N30F, NTR 7450 and NF-PES-10 were analyzed by positron annihilation spectroscopy using slow positron beam analysis. From the depth selective 3 gamma/2 gamma analysis a dense nanoporous filtration layer could be determined. From the depth selective lifetime analysis the size and distribution of the nanopores could be extracted. The measurements indicate the presence of 2 pore sizes in the samples with a radius of 1.25-1.55 angstrom and 3.2-3.95 angstrom. These experimental values are compared with the molecular weight cut-off values of these membranes.