Uncovering the molecular underpinnings of fouling in water purification membranes

Membrane fouling is the irreversible attachment of biological and organic molecules on a membrane surface. The cleaning of fouled surfaces significantly increases the cost of water treatment. Surface modification with coatings containing polar and hydrogen-bond acceptor groups reduces the fouling propensity through the creation of an interfacial hydration layer. Recent studies investigated the interfacial water using molecular dynamics (MD) simulations at various surfaces: proteins, self-assembled monolayers (SAM), and polymers. The results suggest that 1) different geometric arrangements of the same fraction of polar and non-polar groups result in different surface hydrophilicity, and 2) the same macroscopic measures of hydrophilicity give distinguishable structural and dynamic interfacial water properties at the molecular level. In light of these recent findings, we investigated the interfacial water structure, water density fluctuations, and the thermodynamics of foulant binding on commercial polyamide membranes. Using MD simulations, we quantify the hydrophilicity of polyamide surfaces and show how local chemistry and roughness influence overall surface hydrophilicity. This systematic investigation of factors influencing membrane fouling provides valuable insights for the rational design of polyamide membranes.