Role of Roughness Structure in Water Transport through Reverse Osmosis Membranes: Resistance Network Analysis via an...

The polyamide (PA) structure critically influences the water transport behavior of reverse osmosis (RO) membranes. While existing simple transport models are limited to highly simplified PA structures, high-fidelity computational fluid dynamics simulations are both experimentally and computationally expensive. Herein, we propose a novel equivalent circuit model that transforms a complex PA network into an intuitive equivalent circuit comprising basic elements such as exterior, interior, and basal layers. Consequently, the overall transport resistance can be conveniently evaluated via resistance network analysis. The model results agree well with numerical simulations and suggest that membranes with only crumpled exterior layers generally exhibit lower transport resistance. In contrast, the presence of an interior, basal, and/or intrusion layer could potentially increase resistance by a few orders of magnitude. Accordingly, PA structures with an identical exterior appearance could present dramatically different transport resistances and critical transport pathways, highlighting the decisive role of internal structure in regulating water transport. Moreover, the presence of an interior layer could adversely affect surface flux distribution/uniformity, which may have major implications for membrane fouling. This study provides an intuitive framework to understand water transport in RO membranes and provides critical guidelines for membrane structure optimization.