Abstract
Effect of the co-ion on the membrane permeability coefficient was studied theoretically and confirmed experimentally for cellulose membrane and for bovine lens capsule. When the mobility of the co-ion was much larger than that of the counter-ion, the reduced membrane permeability coefficient, Pγ, became larger than 1.0 and had a maximum value in the concentration range where the concentration of solution was almost equal to the charge density of the membrane. The permeability coefficient defined on the basis of the concentration gradient in the membrane, P*, and the diffusion potential, εD, in the membrane were estimated from experimental data. and also calculated theoretically. The agreement between experimental and theoretical values was good and values of both P* and εD increased in the same concentration range as Pγ became larger than 1.0 if the mobility of the co-ion was much larger than that of the counter-ion. It was concluded that, in the concentration range where the concentration of solution is almost equal to the charge density of the membrane, the reduced membrane permeability coefficient becomes larger than 1.0 and has a maximum value because the diffusion potential εD in the membrane has a maximum value and the the value of P* increases in this concentration range.
