Atomic force microscopy of dense and asymmetric cellulose-based membranes

The surface structures of dense and integrally skinned cellulose acetate (C A) and cellulose acetate butyrate (CAB) membranes, prepared by phase invers ion under different casting conditions, are investigated by tapping mode at omic force microscopy (TM AFM). The results obtained show that: (i) The top and bottom surfaces of the dense CA membrane were quite uniform in compari son with the corresponding faces of asymmetric CA and CAB membranes. Despit e the casting conditions the active and support layers of the asymmetric me mbranes display large differences on the roughness parameters. (ii) The asy mmetric membranes prepared with an organic system as a non-solvent pore-for mer (method IV) display smaller nodule aggregates and lower values of the r oughness parameters than the ones prepared using an inorganic system as swe lling agent (method I). This is more pronounced for the CA membranes than f or the CAB membranes. (iii) In the active layer of asymmetric CA membranes casted at longer evaporation times, the measured values of surface roughnes s parameters tend to decrease. Also, for these CA membranes, as the evapora tion time increases the average size of the depression areas observed on th e surface decreases. The laboratory-made CA and CAB membranes display a wide range of nanofiltra tion and reverse osmosis permeation characteristics. These characteristics are correlated to surface roughness parameters of the active layers. (C) 19 99 Elsevier Science B.V. All rights reserved.