A Monte Carlo simulation has been used to model the effects of medium-energy ion-beam modification of Nafion. With typical ion energies of 100-200 keV, the treatment affects the outer 0.5-2-mum surface layer. An equation has been developed for predicting the expected range of implantation as a function of the ion energy and atomic number. The expected range of displacement damage due to the ion beam can similarly be described over the whole parameter range of interest with a double logarithmic fit. A full characterization of the distributions with their first four statistical moments is also presented. The quantitative description of the profiles obtained is useful for the rational design of an ion-beam treatment for the preparation of integrally skinned membranes. (C) 2004 Wiley Periodicals, Inc.