Membrane surface roughness characterization and its influence on ultrafine particle adhesion

Knowledge of the surface properties of ceramic membranes is useful for understanding and improving their filtration performance. In this study surface roughness was determined using a surface roughness tester (SRT). Roughness values were found to increase with increasing scan-length up to a scan-length of 4 mm after which it remained relatively constant. Scanning electron microscopy (SEM), vertical scanning interferometry (VSI) and atomic force microscopy (AFM) were used to characterize the membrane morphology. Compared to AFM, VSI and SEM allow for rapid and accurate characterization of membrane roughness at substantially larger scan-sizes. Static adhesion tests showed that rougher surfaces have more adhesion to nanosized particles than smooth ones. In crossflow filtration, adhesion of nanosized particles smaller than or similar in size to the asperities depended mainly on the membrane roughness. At a certain roughness, a highest flux was obtained. But for microsized particles larger than the asperities, roughness had no evident effect on the flux. According to experimental results and the estimation of hydrodynamic forces acting on particles, fouling could be controlled by modification of surface roughness of ceramic membranes.