Molecular Dynamics Simulations of a Poly(ethylene glycol)-Grafted Polyamide Membrane and Its Interaction with a Calcium Alginate Gel.

Molecular dynamics simulations are carried out to investigate the antifouling property of a polyethylene glycol (PEG)-grafted polyamide (PA) membrane. Our specific interest is the computational study of the interaction between a grafted PEG coating and an alginate gel foulant by a steered molecular dynamics approach. Simulation results show that the PEG coating can hold a tightly bound hydration water layer. When the alginate gel is dragged to approach the PEG coating surface, a strong repulsive hydration force is observed due to the compression of this hydration layer. Detailed calculations of the potential of mean force (PMF) show that the repulsive interaction between the alginate gel and the hydration water layer around the PEG coating has a dominant contribution to the total repulsive PMF. We have also studied the effect of the PEG coverage on the membrane-foulant interactions. We find that the alginate gel has a strong tendency to drift to the uncovered PA membrane surfaces (namely, the PEG hollows). However, direct attachment of the gel to the PA membrane surface can be avoided if the gel size is slightly larger than the PEG hollow site.