PROPERTIES OF HYDROGEL MEMBRANES OF POLY(VINYL ALCOHOL) AND POLY(ACRYLIC ACID) UNDER A PRESSURE-GRADIENT

The dependence of the electric potential difference on time under a pr essure gradient across hydrogel membranes, obtained by esterification of poly(vinyl alcohol) and poly(acrylic acid), was measured. At the mo ment when a pressure difference was applied, a sharp spike of the elec tric potential difference was observed. The overall variation of the e lectric potential difference on time consisted of two different proces ses. One of them, which gradually increased with time, and finally rea ched a steady-state value, reflects a relaxation of polymer chains dis solved in the liquid phase of the gel membrane under the pressure diff erence. The other, which showed a sharp inverse spike just after apply ing the pressure difference, and reached zero immediately, may have be en caused by a transformation of the membrane matrix due to a sudden c hange in pressure before the migration of the water, that is, by compa ction of the membrane matrix. When hydrogen molecules of the carboxyl groups in the gel membrane were exchanged with potassium ions, the gel membrane expanded. The relationship between the magnitude of the elec tric potential difference for each of the forms and the properties of the membranes is discussed.