Mechanism of oil detachment from hybrid hydrophobic and hydrophilic surface in aqueous solution

In this paper, the detachment mechanism of alkane molecules from one hybrid hydrophobic and hydrophilic solid surface was studied by molecular dynamics simulation. First, some alkyl chains were linked through C-O bonds with silica surface to get one half-hydrophobic one, and the other half-hydrophilic area was still same as silica surface, thus one modified hybrid hydrophobic and hydrophilic silica surface was constructed. Second, some alkane molecules were adsorbed on the hybrid surface to get one whole hydrophobic oil layer, and the detachment mechanism of alkane molecules on the surface was discussed in aqueous solution using molecular dynamics. The simulated results showed that the key to the detachment of alkane molecules is the formation of water channel in oil layer between water phase and solid surface. In the detachment process, water molecules can penetrate oil layer to the silica surface through the strong H-bonding interaction among water molecules in water channel, and soon these molecules can form a gel layer along the silica surface by fast diffusion under the H-bonding interaction and electrostatic interaction between water molecules and silica surface. At last, the half-hydrophilic area on hybrid surface becomes hydrophilic again after the oil layer's detachment, and alkane molecules aggregate on the modified surface linked the alkyl chains. For the hybrid surface, some of alkane molecules insert into the interstice among the alkyl chains, and thus the oil drop cannot be dispatched thoroughly from the surface linked alkyl chains in aqueous solution. Our results showed that the detachment mechanism of oil from hybrid surface is different, compared with the whole pure hydrophilic surface.