We investigated the water flux through neutral carrier membranes cause
d by the osmotic pressure difference of the solutions on both sides of
these membranes. Miniaturized thin-film ion-selective electrodes were
used as their extremely small internal electrolyte volume as well as
their extremely thin membrane make them specifically suitable for such
studies. The dilution of the internal electrolyte due to the transmem
brane water nux results in a significant shift of the ISE potentials.
A model explaining the potential versus time curve of thin-film sensor
s was developed. The penetration coefficient of water is determined ex
perimentally with respect to the lipophilicity of the membrane plastic
izer used. The inverse of the square root of the penetration coefficie
nt depends linearly on the logarithm of the lipophilicity for almost a
ll investigated membranes.