A radiotracer technique for measuring solute diffusion with zero concentration gradient: diffusion of benzoic acid through polyethylene film

A simple glass apparatus has been designed to allow the study of solute diffusion under conditions of zero concentration gradient. Solutions of equal concentration of the solute, one containing the solute in radiolabelled form, are separated by a polymer membrane, and the diffusion of radionuclide is monitored. The system studied involves solutions of benzoic acid in toluene, separated by polyethylene film. The results show that the benzoic acid diffuses through the polymer film in monomeric form, despite that fact that it is almost 100% dimerized in the solution phase. (author)