Diode-like single-ion track membrane prepared by electro-stopping

The preparation of an asymmetric membrane in poly(ethylene terephthalate) ( PET) is described, using a combination of chemical and electro-stopping. Fo r this purpose, a single-ion-irradiated PET film is inserted into an electr olytic cell and etched from one side in 9 M sodium hydroxide while bathing the other side in a mixture of 2 M KCl and 2 M HCOOH (1:1 by volume), elect rically retracting the OH- ions from the tip of the etch pit during pore br eakthrough. When a preset current has been reached, the etch process is int errupted by replacing the etching solution with acidic 1 M potassium chlori de solution. After etching, the current-voltage (I-V) characteristic is det ermined under symmetric bathing conditions, immersing both sides of the mem brane in KCI solutions of identical concentration (0.01-1 M) and pH (3-8). The I-V characteristic is strongly non-linear, comparable to that of an ele ctrical diode. If the polarity during etching is reversed, pushing the OH- ions into the tip of the etch pit, the resulting pores are larger and the d egree of asymmetry smaller. The importance of electro-stopping is compared with chemical stopping. (C) 2001 Elsevier Science B.V. All rights reserved.