Tj. Chou et A. Tanioka, IONIC BEHAVIOR ACROSS CHARGED MEMBRANES IN METHANOL-WATER SOLUTIONS -2 - IONIC MOBILITY, JOURNAL OF PHYSICAL CHEMISTRY B, 102(1), 1998, pp. 129-133
The permeability coefficients across cation-and anion-exchange membran
es were measured for LiCl methanol-water solutions. The experimental d
ata were analyzed on the basis of the Donnan equilibrium and the Nerns
t-Planck equation of ion flux considering the effect of the mean activ
ity coefficient of an electrolyte in an external solution, and the the
oretical predictions agreed well with the experimental data. The mobil
ities of ions in the membrane were determined by using the results of
the effective membrane charge densities and the cation-to-anion mobili
ty ratios obtained from the previous paper and a nonlinear regression
method. The results showed that the mobility of ions in the membrane w
ould decrease with an increase in the weight fraction of methanol. It
is postulated that the counterions prefer to make ion pairs with the f
ixed charge groups in the mixed solvent system since the dielectric co
nstant of methanol is smaller than water. Thus the ion pairs between t
he counterions and fixed charge groups will increase with the increase
in methanol concentration, and the mobilities of the counterions will
decrease.