The change in roughness of polyethersulfone (PES) ultrafiltration membranes by plasma treatment is quantified by atomic force microscopy (AFM). A wavelet-based analysis of surface morphology images from AFM is used to evaluate the surface roughness changes of polymeric membranes. Discrete wavelet transform with 3D image analysis is used to capture patterns at all relevant frequency scales-which are not possible with other traditional techniques of image analysis. The hydrophilic nature and roughness of the membrane surfaces are related to fouling over the membrane surfaces with associated change in solvent flux. The changes in flux of the plasma treated membranes are quantified by measuring the enhancement in flux of a model solution of bovine serum albumin (BSA). The results clearly demonstrate that a PES membrane being more hydrophilic and having smoother surface by optimal treatment of cold CO2 plasma is easier to clean and the augmented permeability can be retained in successive use. (C) 2008 Elsevier B. V. All rights reserved.