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The average pore size and the pore size distribution of reverse osmosis membranes have been determined on the basis of the surface force-pore flow model by use of separation data of reference solutes. The results confirm the correspondence between the pore size distribution of unshrunk membranes and the shrinkage temperature profile proposed by Kunst and Sourirajan. The change in the pore size of unshrunk membranes to those of membranes shrunk at various temperatures is further related to the change in the thermodynamic properties associated with the movement of polymer molecules. The significant effect of the type of pore size distribution on the fractionation of solute molecules is also illustrated.

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The average pore size and pore size distribution on the surface of membranes made from cellulose and different cellulose acetate materials, and obtained by shrinkage in hot water at different temperatures, were determined on the basis of the surface force-pore flow model for reverse osmosis transport. It was found that the two Gaussian normal distributlons-model applied to the pore size distributions of membranes Involved in this study. From data on the change in pore radius at different shrinkage temperatures, the relative variations in the free energy changes Involved could be quantitatively ascertained as a function of the pore radius and the acetyl content of the membrane material; such variations could be further related to the regularity in the macromolecular structure of the cellulosic membrane materials used.