Osmotic Effects in Track-Etched Nanopores

Asymmetrically etched ion-track membranes attract great interest for both fundamental and technical reasons because of a large variety of applications. So far, conductometric measurements during track etching provide only limited information about the complicated asymmetric etching process. In this paper, monitoring of osmotic phenomena is used to elucidate the initial phase of nanopore formation. It is shown that strong alkaline solutions generate a considerable osmotic flow of water through newborn conical pores. The interplay between diffusion and convection in the pore channel results in a substantially nonlinear alkali concentration gradient and a rapid change in the pore geometry after breakthrough. Similar phenomena are observed in experiments with cylindrical track-etched pores of 15-30 nm in radius. A theoretical description of the diffusion-convection processes in the pores is provided.