Transport processes during the incubation time of ion track etching in polymers

The processes which take place in polymers before visible etch track formation sets in after exposure to alkaline solutions, i.e. during the so-called "incubation time", are thought to consist of the penetration of the liquid into the polymer and the polymer's subsequent glassy-to-rubbery phase transformation. We have studied systematically the first of these steps - the penetration process - by measuring the depth distributions of tracer ions dissolved in the penetrant solutions in different polymers as a function of pH value, temperature, and penetration time. Determination of the free volume of pristine and ion-irradiated polymers by positron annihilation spectroscopy served as an additional important source of information. Our findings show that the solutions' penetration is often a highly complex process which eventually dominates the overall incubation time.