Water transport mechanisms during pressure-driven transport through polyamide nanogaps

Molecular-scale simulations of pressure-driven transport through polyamide nanogaps (5-100 Å) were performed to investigate fundamental transport mechanisms. Results show that transport in nanogaps <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mo>≤</mml:mo></mml:math> 10 Å is always subdiffusive, but superdiffusive transport was observed in nanogaps <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mo>≥</mml:mo></mml:math> 20 Å. Near typical operating pressures for applications ( <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:mo>Δ</mml:mo> <mml:mi>p</mml:mi></mml:mrow> </mml:math> = 100 atm), only the 100 Å nanogap exhibited superdiffusive behavior. Since openings in common membrane materials are typically <20 Å, results indicate that subdiffusive to diffusive transport dominates for typical applications, such as reverse osmosis.