Creation of Nanostructure-Controlled Functional Membranes Using High-Energy Ion Beams

Abstract

The development of micro/nanofabrication techniques for organic polymers is essential to facilitate their potential future applications. This paper is devoted to the following two topics, i.e.,ion-track-etched porous membranes and ion-track-grafted electrolyte membranes for fuel cells and other electrochemical applications. Both membranes involve the creation of nanostructured functional membranes with swift heavy ions. Latent tracks of the MeV-GeV heavy ions in polymer films can be chemically etched to produce membranes with micro- and nano-sized through-pores, termed ion-track-etched membranes. Our focus was on track-etched membranes of poly（vinylidene fluoride）（ PVDF）, which was also considered as a matrix of polymer electrolyte membranes. Although the PVDF-based racketched membranes have already been investigated, their preparation methods have never been optimized. The etching behavior mainly depended on the energy deposition of the ion beams, and thus its depth distribution, which was estimated with theoretical simulations, was successfully applied to control the shapes and diameters of the etched pores. The cation and anion exchange membranes （CEMs and AEMs） for fuel-cell devices and separation processes were prepared by ion-track grafting, which involves direct graft polymerization into latent tracks in pol（y ethylene-co-tetrafluoroethylene）（ ETFE）. Interestingly, the resulting membranes exhibited an anisotropic ion transport, i.e., higher conductivity leading to lower resistance in the thickness direction. As determined from icroscopic observations, this is probably because the nearly columnar electrolyte phase with width ranging from tens to hundreds of nanometers extended through the membrane. This controlled structure also exhibited excellent membrane properties, e.g., high dimensional stability and low water permeability, which promoted investigations into novel electrochemical separation processes using ion-track-grafted CEMs and AEMs. Finally, worldwide recent advancements in irradiation technologies are presented to explore the potential industrial applications of our new functional membranes.