Nanoprobe imaging molecular scale pores in polymeric membranes

► A new nanoprobing technique to measure the pore size in nanofiltration membranes. ► Skin layer thickness of the integrally skinned asymmetric membranes was measured. ► Measured pore size correlates well with nanofiltration performance. ► Nanoparticle size in the permeate is comparable to the measured pore size. ► It has been proposed that size exclusion is the separation mechanism for asymmetric P84 membranes.