Unveiling the Antifouling Mechanism of Polyester and Polyamide Membranes against Alginate Fouling via Molecular Dynamics Simulations.

Global freshwater scarcity is intensifying, and membrane-based technologies play a pivotal role in seawater desalination and wastewater treatment. However, the complex mixture of impurities and foulants in seawater readily degrades membrane performance, potentially leading to irreversible damage or loss of functionality. This makes the elucidation of antifouling mechanisms a critical research priority. Based on traditional experience, the reason for alginate fouling of the membrane is the strong interaction between alginate and the membrane, which leads to the accumulation of foulants and causes membrane fouling. In this study, we used molecular dynamics simulations to propose a new fouling mechanism: specifically, the competitive adsorption of Ca by alginate and the membrane is the main reason for the intensity of membrane fouling. We compared the polyamide (PA) membrane and polyester (PE) membrane constructed by the self-heuristic method to verify the morphology and flux performance of the model, ensuring the authenticity and rationality of the model. Furthermore, we clarified the competitive adsorption mechanism through the equilibrium molecular dynamics (EMD) nonequilibrium molecular dynamics (NEMD) and density functional theory (DFT) methods. The simulations reveal that alginate bridges to the membrane through Ca causing fouling of the membrane. Alginate and the membrane jointly adsorb Ca. Under the action of competitive adsorption, the amide groups in PA membranes generate a more negative surface electrostatic potential (minimum value: -51.44 kcal/mol) compared to PE membranes (-41.86 kcal/mol). This heightened negativity stabilizes the formation of Ca salt bridges on PA surfaces, enhancing the competitive effect with alginate and exacerbating fouling, whereas the relatively weaker competitive effect on PE membranes confers superior antifouling properties. Quantum chemical calculations further confirm that PE membranes possess lower coupling and dimer binding energies than PA membranes, which is a key molecular factor underpinning their antifouling superiority. Kinetic analysis additionally shows that PE membranes exhibit faster decay of weak alginate-membrane interactions, higher interaction turnover rates, and lower binding probabilities, further reinforcing their antifouling advantage. Collectively, these insights establish a theoretical framework for the molecular design of next-generation, high-performance antifouling membranes.