Modeling Water Transport in Interlayered Thin-Film Nanocomposite Membranes: Gutter Effect vs Funnel Effect

Interlayered thin-film nanocomposite (TFNi) membranes have experimentally demonstrated a great potential for achieving major gains in water permeance over conventional thin-film composite membranes, making them promising candidates for many environmental applications. Nevertheless, existing literature often reports contradicting observations on the effectiveness of interlayers. In this study, we implement a three-dimensional solution-diffusion model to analyze a geometry-induced funnel effect and an interlayer-promoted gutter effect. Our simulation results suggest that even an ultrathin interlayer of a few nanometers in thickness could serve as a low-resistance gutter layer, which minimizes the transversal water transport in the less permeable polyamide layer and thereby mitigate the unfavorable funnel effect. The actual available water permeance is bounded by the ideal polyamide-limited upper bound and the substrate-limited lower bound, with the interlayer regulating the competition between the funnel effect and the gutter effect. Water permeance can be potentially improved by an order of magnitude with the interlayer, and this enhancement is more pronounced for thinner polyamide layers, less porous substrates, and more permeable interlayers. We further analyze the role of the interlayer on improving the flux distribution/uniformity over a membrane surface, which has major implications on membrane fouling propensity. Our study establishes a theoretical framework for understanding the fundamental transport mechanisms in TFNi membranes, which provides important guidance on the future development of high-performance desalination membranes.