The complex influence of membrane roughness on colloidal fouling: A dialectical perspective

Abstract

Roughness is a key feature of membrane surface topography, yet its impact on fouling remains unclear. Herein, we present a coupled collision attachment-wettability framework to investigate the impact of membrane roughness on fouling from a dialectical perspective. Our findings show that for hydrophilic membranes, increasing surface roughness enhances the interfacial hydration repulsion barrier, reducing fouling. In contrast, for hydrophobic membranes, rougher surfaces lower the interfacial energy barrier, increasing fouling. The effect of roughness is also influenced by the membrane's intrinsic contact angle (θ₀), initial water flux (J₀), and solution ionic strength (I_s). Membranes with lower θ₀ maintain higher stable flux, even when smooth, while fouling resistance for higher θ₀ membranes depends more on surface roughness. At lower J₀ or I_s, flux remains relatively stable with slight/mild reductions, due to reduced permeate drag or enhanced electrostatic repulsion. In contrast, severe fouling occurs under high J₀ or I_s, irrespective of surface roughness. Our simulations reveal the various mechanisms (i.e., hydration repulsion, permeate drag, and electrostatic interactions) that govern the role of surface roughness in fouling, providing valuable implications for membrane design, operational optimization, and feedwater pretreatment.