Molecular investigation of oil-water separation using PVDF polymer by molecular dynamic simulation

In this study, adsorption of water nanodroplets, oil nanodroplets and oil-water mixtures on a poly vinylidene fluoride (PVDF) surface is investigated computationally by a molecular dynamics (MD) approach and a mechanism for adsorption of the droplets is proposed. MD simulation results revealed that the PVDF surface is hydrophobic and oleophilic and can be used to separate oil from water. The acquired results are in good agreement with experimental results. As to investigate the origins for hydrophobicity of the PVDF surface, mobility of water molecules on the PVDF surface has been meticulously investigated. Investigations have proven that once the water molecules are organized singly or in small groups with two or three molecules, they exhibit very low levels of mobility, whereas water molecules in groups of four or more have high mobility. Some descriptive studies were performed based on MD simulation results to investigate the behavior observed in the systems including: (i) distribution of partial charges on the surface of PVDF. (ii) Dependence of the orientation of water molecules near the PVDF surface on the size of water cluster. (iii) Dependence of the distance of water molecules to the PVDF surface on the water cluster size. Manner of charge distribution on the PVDF demonstrated a formation of nanodomains with positive and negative charges on the surface. Dependence of the behavior of water molecules on the nano-domains on the water cluster size was investigated.