R. Kiyono et al., PROPERTIES OF HYDROGEL MEMBRANES OF POLY(VINYL ALCOHOL) AND POLY(ACRYLIC ACID) UNDER A PRESSURE-GRADIENT, Bulletin of the Chemical Society of Japan, 68(3), 1995, pp. 810-815
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.