Molecular dynamics simulation study of oil slippage on polymer grafted surface: The role of grafting density

The polymer grafted materials are frequently used in antifouling and oil-water separation, while the microscopic mechanism of liquid slippage on this surface remains unclear. This study uses molecular dynamics (MD) simulations to explore the structure and transport of oil (n-hexadecane) on polydimethylsiloxane (PDMS) grafted surface as a function of grafting density. Simulation results indicate that PDMS chain structure undergoes a transition from liquid-like to solid-like structure when the grafting density increases. As a result, the entanglement between the PDMS and n-hexadecane is also weakened. The direct consequence of this structural change is that the slip length of n-hexadecane shows a non-monotonic dependence on the grafting density, and a maximum slip length appears at intermediate grafting density. Further analysis indicate that the slip length also increases as the applied shear rate increases, which facilitates the transport of fluid at the grafted surface. These simulation results illustrate the subtle interplay between polymer-alkane interface structure and the transport property of the fluids, which are consistent with recent experimental studies, and will be helpful for rational design of polymer grafted materials in separation technologies. image