Wetting-Governed Heterogeneous Nucleation on Corrugated Reverse Osmosis Membranes: <i>f</i> (θ) Outperforms Ra as a Predictor of Scaling

Roughness plays an important role in scaling on reverse osmosis (RO) membranes, yet the underlying mechanisms remain unclear. Here, we investigate the scaling behavior of three polyamide composite RO membranes (RO-L, RO-M, and RO-H) with systematically varied surface roughness. By tracking scaling evolution and introducing a wetting factor, f(θ), we elucidate how the surface microstructure regulates heterogeneous nucleation. Membranes with lower f(θ) values exhibited a delayed scaling onset (flux decline <20%), attributed to a larger effective filtration area and enhanced local turbulence that suppressed early gypsum deposition. However, their ridge-like structures also led to more irreversible scaling. Notably, f(θ) showed a stronger correlation with scaling propensity than average roughness (Ra), highlighting wetting characteristics as a more reliable descriptor.