Role of Interfacial Structure of Water in Polymer Surface Wetting

We present a theoretical approach to investigate the structures and contact angles of water in contact with different polymer surfaces. In the theoretical approach, the three-dimensional reference interaction site model integral equation and the three-dimensional density functional method are combined through the bridge function. First, the three-dimensional distribution functions of water over the crystalline polyethylene surface and the amorphous polyethylene, polypropylene and polystyrene surfaces are calculated. According to the isosurface representations of the distributions, the wetting processes of these four polymer surfaces are simply analyzed. Then, the three-dimensional distributions of free energy are calculated by the density functional equation to obtain the interfacial tensions. Finally, the contact angles are estimated. It is shown that the predicted contact angles are in good agreement with the literature data, indicating that above structure and energy descriptions are quantitatively reasonable.