Do the soft-etched and UV-track membranes actually have uniform cylindrical subnanometer channels?

Abstract

Bioinspired nanoporous membranes have attracted great attention because of their potential for ion separation. Radiation-based approach to the fabrication of ion-selective subnanoporous and nanoporous membranes includes irradiation of polymer films with accelerated heavy ions and further physico-chemical treatment. This study aims at better understanding of the mechanisms responsible for the formation of ion-permeable and ion-selective channels in biaxially oriented polyethylene terephthalate films bombarded with heavy ions and treated with soft ultraviolet (UV) radiation. The amount of matter removed from the films by energetic ions and by liquid extraction is measured and compared with the amount of carboxyl groups produced by the ion and UV exposure. The change in electrical conductivity of the films during the liquid extraction is studied depending on the atomic number of bombarding ion, ion fluence, temperature, mechanical stress, and properties of starting material. Examination of samples irradiated at different angles shows that interconnection of ion tracks in the membrane bulk drastically enhances the ionic permeability by reducing the intrapore energy barrier. It is shown that molecular relaxation and internal stress play a significant role in the formation of the ion-conductive structure in the ion-irradiated polymer. The resulting structure resembles a heterogeneous ion-exchange membrane.