Membrane Fouling: Does Microscale Roughness Matter?

The surface of thin-film composite membranes used for reverse osmosis appears to be rough, known as a peak-valley morphology, and this is believed to cause more severe fouling than would occur for a smooth surface. In this study, polyamide nanofilms were made by interfacial polymerization on a sacrificial layer or at a free aqueous/organic interface, manipulating the surface from ultrasmooth (roughness ca. 0.2 nm) to crumpled (roughness ca. 80 nm) morphology. This approach enables the fabrication of morphologically similar polyamide nanofilms on different support membranes, and the control of their initial flux. Membranes with higher initial flux are more severely fouled while their surface roughness (either smooth or rough) is held constant. Moreover, when they are provided with the same initial flux, smooth and rough membranes showed insignificant differences in flux decline upon fouling. This teaches that it is the initial flux, rather than the surface roughness, which is the dominating factor influencing membrane fouling.