Molecular simulation of the hydrodynamics of water in contact with hydrophilized poly(vinylidene fluoride) surfaces

Modeling electro-kinetic effects of aqueous solutions on charged polymer surfaces constitute great challenges. The interplay of water pH and salt concentration with surface charges at the nanoscale and macroscopic collective hydrodynamics leads to a rich phenomenology, including the hydrophobic/hydrophilic nature of the polymer surface. The present work aimed at contributing to the modeling of these phenomena for a specific system: Poly(vinylidene fluoride) (PVDF), including a surface functionalization by carboxylic groups. We report on molecular dynamic simulation of water interactions under imposed hydrodynamics with a flat PVDF surface functionalized with charged groups and buffered by sodium ions. Using this approach, we simulate the velocity and density profiles of water as a function of the functionalization. By using averaged charge distributions, the electrostatic surface potential at the mean field level, and hence the zeta potential, is also given. Deviations from Navier-Stokes type hydrodynamics at nanoscales are given and we found, in accord with experimental findings, that PVDF gets wet in contact with water. The observed dependencies of the hydrodynamics at nanoscales sheet light on the potential use of functionalized PVDF for instance as a membrane material for water filtration purposes.