Characterizing the Hydrophobicity of Surfaces Using the Dynamics of Interfacial Water Molecules

S Bekele and M Tsige, JOURNAL OF PHYSICAL CHEMISTRY C, 122, 9015-9020 (2018).

DOI: 10.1021/acs.jpcc.8b01353

As most interfacial processes of practical interest occur in aqueous media where the presence of water may have an impact on desired functional properties, it is important to understand the structural and dynamical properties of interfacial water. Using molecular dynamics simulations, we investigated the properties of interfacial water molecules in contact with model atactic polystyrene surfaces of varying polarity. We find that interfacial water molecules, which do not make hydrogen bonds with the substrate, have a faster dynamics and appear to have a universal water-water hydrogen bond relaxation time of about 5 ps. The diffusion coefficients and the relaxation times of the water molecules involved in hydrogen bonding with the surface, on the other hand, have strong dependence on surface polarity and reveal a hydrophobic to hydrophilic transition regime with contact angle in the range of 40-50. The results presented will be of broad interest to researchers working in the area of surface science, biotechnology, nanotechnology, and in all forms of coating applications.

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