T. Murata et al., An application of percolation theory to the electrolyte penetration through porous water-swollen cellulose triacetate membrane, J COLL I SC, 220(2), 1999, pp. 250-254
Permeability coefficients P of KCl through porous cellulose triacetate (CTA
) membranes were measured as a function of the water volume fraction V-W an
d diffusion coefficients D were determined using solubility parameters K an
d a membrane thickness d from the relationship of P = KD/d. D increased wit
h an increase in V-W. D especially increases abruptly around V-W = 0.5, whi
ch corresponds to 2% triethylene glycol (TEG) content. The percolation theo
ry was applied to the experimental results under the conditions D-A = D (V-
W = 1) = 1.8 x 10(-5) cm(2) s(-1), D-B = D(V-W = 0) = 1.8 x 10(-8) cm(2) s(
-1), coordination number (Z) = 2.5, 3, 3.5, and 4, and packing fraction f =
1.0. A good fit was obtained at Z = 3.5 because the experimental and calcu
lated results also shifted at the same V-W below V-W = 0.5. It is suggested
that a phase inversion, that is, change of a discontinuous water phase to
a continuous water phase, occurs around V-W = 0.5. Above V-W = 0.5, the exp
erimental results agree well with the calculated line for Z = 3 or Z = 2.5
which means that the coordination numbers decrease with an increase in wate
r content. It is thought that V-W is overestimated because it is hard to co
mpletely wipe off the excess water quickly from the membrane surface. Z = 3
.5 means that a pore can connect in 3.5 directions. (C) 1999 Academic Press
.