DIFFERENTIAL PERMEATION .1. A METHOD FOR THE STUDY OF SOLVENT DIFFUSION THROUGH MEMBRANES

We describe the differential permeation method for the study of the di ffusion of solvents from a liquid (or liquid mixture) through flat or tubular membranes. This method consists of measuring the transient per meation rates through the membrane when one of its faces is suddenly p ut into contact with the liquid medium. The change in the transient ra te with time is analyzed by numerical best fitting methods to determin e the Fickian diffusion coefficient. A simplified equation is proposed for the fitting of the response of a tubular membrane. Deviations fro m the Fickian transport mechanism with concentration-independent diffu sion coefficient can be evidenced and eventually analyzed by using oth er mechanistic models.