Structure of polycarbonate track-etch membranes: Origin of the “paradoxical” pore shape

The process of pore formation in ion-irradiated polycarbonate films on treatment with alkali solutions in the presence of a surfactant is studied. It is found that the pore shape depends on both the structure of the initial films and the peculiarities of the interaction of the surfactant with the polymer surface and the transport of the surfactant into tracks. Due to heterogeneity of the films the diameter of a track pore channel varies along its length. The presence of the surfactant results in a further effect. Surfactant molecules adsorb on the solution/polymer interface at the pore entries and reduce the etch rate which leads to formation of cigar-like pore channels. The use of surfactant as a component of chemical etchant enables one to control the pore shape in track membranes thus optimizing their retention and permeation properties.