Ji. Calvo et al., BULK AND SURFACE CHARACTERIZATION OF COMPOSITE UF MEMBRANES ATOMIC-FORCE MICROSCOPY, GAS ADSORPTION-DESORPTION AND LIQUID DISPLACEMENT TECHNIQUES, Journal of membrane science, 128(1), 1997, pp. 7-21
In this work, the pore size distributions referred to volume, surface
and number of bulk pores, along with the internal surface area and the
size parameters of surface pores are determined for two polyethersulp
honic microporous composite membranes of nominal MWCO of 4000 and 3000
0 Da. The microporous support pore size distribution has also been obt
ained. These goals have been achieved using several characterization t
echniques: atomic force microscopy (AFM), N-2 adsorption-desorption at
77 K and a liquid displacement technique. A computerized analysis of
the AFM micrographs allowed determination of the pore size distributio
n of surface pores at different magnifications. Also, surface roughnes
s can be obtained. Adsorption isotherms, combined with the BET theory
for multilayer adsorption, allowed determination of the internal surfa
ce area of the membrane, while the volume, surface and pore number dis
tributions were calculated from the Kelvin equation, both in the desor
ption process to obtain the so-called mesopore distribution. Further a
nalysis, by extending the pore size analysis to pores where the Kelvin
equation is not valid, allowed determination of the micropore distrib
ution. Finally, the membrane support has been detached and analyzed by
a modified bubble point or liquid displacement technique. Analysis an
d comparison of all results show that several pore populations (includ
ing micro- and mesopores) are present in the membrane with considerabl
e differences between surface pores and bulk pores, the latter being t
hose which should determine permeation. Two further mese- and macropor
e populations could be assigned to the membrane-support transition or
the support itself.