Permeabilities (P), diffusion coefficients (D) and time lags (Theta) for wa
ter, alcohols and carboxylic acids passed through undoped and doped polyani
line membranes are reported. Permeabilities through undoped polyaniline are
stable and linear, but both permeabilities and diffusion coefficients tend
to be low. As an example, for water, P=0.111+/-0.05 g mm/m(2) h, with a di
ffusion coefficient of D=5.0x 10(-10) cm(2)/s. Methanol has the highest per
meability through undoped polyaniline (P=0.83+/-0.02g mm/m(2) h), despite i
ts small diffusion coefficient (D=1.5x10(-10) cm(2)/s). Fully HCl-doped pol
yaniline membranes have higher permeabilities (up to 5-6 g mm/m(2) h) with
correspondingly larger diffusion coefficients (e.g. D-water>1.0x 10(-8) cm(
2)/s) and shorter time lags. Larger alcohols (e.g. 2-propanol) and carboxyl
ic acids (e.g. acetic acid) show no permeation through doped polyaniline. T
herefore, fully HCl-doped polyaniline membranes can be used to effectively
separate water from acetic acid (alpha H2O approximate to 200). Unfortunate
ly, when HCl-doped polyaniline is used as a pervaporadon membrane, the perm
eation rates of the feed decline over time. For example, the permeability o
f water declines from a high of similar to 2.5 g mm/m(2) h to a much lower
average steady-state value of 0.3 g mm/m(2) h over 48 h. This effect has be
en traced to the leaching of HCl dopants out of the polyaniline membrane an
d into the feed solution. The problem of dopant leaching can be eliminated
by using a polymer dopant in a blend with polyaniline. The permeation rates
of ethanol/water feeds through blends of 10 wt.% polyamic acid/90 wt.% pol
yaniline and 10 wt.% polyacrylic acid/90 wt.% polyaniline are linear and st
able. This demonstrates that polymeric dopants eliminate the problem of dop
ant leaching. Both blends possess permeabilities and selectivities in-betwe
en undoped and doped polyaniline. (C) 2000 Elsevier Science B.V. All rights
reserved.