L. Zeman, ARE PORE-SIZE DISTRIBUTIONS IN MICROFILTRATION MEMBRANES MEASURABLE BY 2-PHASE FLOW POROSIMETRY, Journal of membrane science, 120(2), 1996, pp. 169-185
The issue of evaluating equivalent pore diameter distributions in memb
rane microfilters from gas-liquid (g-l) porosimetry data has been crit
ically examined. Experiments performed with one isotropic and one comp
osite anisotropic membrane in both possible orientations revealed cons
picous dependence of the obtained (g-1) porosimetry peaks on imposed p
ressure ramp rates, rho. Interference of this kinetic effect can be el
iminated from the measured data by extrapolation to rho = 0. The ramp
rate effect is most likely caused by tortuous pore length distribution
, and relatively long times required for liquid expulsion. For two exp
eriments, the observed effects of rho could be reconciled with predict
ions of the Schlesinger-Bechhold theory [Bechold et al., Kolloid Z., 5
5 (1931) 172-198]. The data obtained with the thin top layer of the co
mposite membrane facing intruding air directly did deviate somewhat fr
om the theory. Pores characterized by (g-l) porosimetry are likely of
the ''throat type'', and their size distribution is considerably more
narrow than that obtained for the ''node-type'' pores by SEM-image ana
lysis [Zeman and Denault, J. Membrane Sci., 71 (1992) 221-231]. A sing
le bivariate distribution function was constructed for these two disti
nct pore populations. Flow-weighted or number fraction distributions c
an be calculated from the extrapolated porosimetry data. For narrow ra
nges of ''throat'' diameters, these distributions are fairly similar.