Polyacrylate-grafted polyethylene (PE-g-AA) membranes were studied in pervaporation. The membrane performances are improved by an increase in the acrylic grafting ratio. The water and ethanol sorption and diffusion properties in the membrane loaded with different counter-ions, as well as the interactions between the solvent and the membrane ion pairs, were measured. The results show that the ion pairs are preferentially solvated by water, and the water content in the liquid mixture at which the ion pair is dissociated is much smaller for the potassium membrane than for the lithium membrane. The easier dissociation of the K carboxylate ion pair in the water-ethanol mixture explains the increase in the permeability according to the sequence Li+ < Na+ < K+. The apparent contradiction between the sulfonate and the carboxylate membranes with regards to the alkaline cation sequence according to which the permeability changes is explained by the difference in the ionization ability of the sulfonate and carboxylate ion pairs.