The measurement of the permeability of polymer membranes to solvating molecules

Methods previously used to measure the permeability of polymer membranes to solvating liquids and vapors have been reviewed. Experiments with polyethylene and several liquids, notably p‐xylene, indicate that the various methods are not necessarily equivalent. The medium over which the membrane is supported and, more particularly, the nonpermeant pressure differential during permeation are shown to influence the permeation rate. Failure to appreciate this latter fact is believed to be the cause of previously reported anomalies concerning the effect of preswelling on permeation rate and the difference in permeation rate between a liquid and its saturated vapor.