Piezodialysis in weakly amphoteric polymer membranes is discussed from
the viewpoint of non-equilibrium thermodynamics. Succinyl chitosans w
ere used as the weak polyampholytes. With varying pH in the outer solu
tion, the apparent isoelectric point of the membrane was defined as th
e point of zero membrane potential, where solute permeation is much en
hanced. Piezodialysis was confirmed from the phenomenological hydrauli
c permeability coefficients, reflection coefficients and solute permea
bility coefficients of the membrane, which were based on non-equilibri
um thermodynamics. Permeation experiments with mixed ion systems were
also performed. The permeation behaviour was in accordance with that e
xpected for the interactions of ions with polyampholytes in aqueous so
lutions. (C) 1996 Elsevier Science Ltd.