BULK AND SURFACE CHARACTERIZATION OF COMPOSITE UF MEMBRANES ATOMIC-FORCE MICROSCOPY, GAS ADSORPTION-DESORPTION AND LIQUID DISPLACEMENT TECHNIQUES

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.