Investigation of the wettability of chemically heterogeneous smooth and rough surfaces using molecular dynamics simulation

Increasing the hydrophobicity of polymeric surfaces, particularly polydimethylsiloxane (PDMS), has recently been the focus of research. In the present work, the wettability of smooth and rough PDMS surface was investigated. Surfaces with different chemical heterogeneity were examined for hydrophobicity using molecular dynamics simulation. In order to simulate surfaces with different heterogeneities, several distributions for the placement of polymer-forming atoms were taken into account. In addition, roughnesses with different distributions of the constituent atoms were applied to the polymer surfaces to increase hydrophobicity. As an indicator of the hydrophobicity, the contact angle was calculated using two approaches. Regarding the chemical heterogeneity of the polymeric surface, the simulation results showed that the contact angle and the radius of water droplets on the surface depended on the constituent atoms and their number, so that surfaces with more carbon atoms offered larger contact angles and smaller droplet radius, and thus more hydrophobicity. Furthermore, roughnesses rich in carbon also increased the surface hydrophobicity. It was concluded that the distribution of the constituent atoms of the polymeric surfaces played an essential role in water dispersion in that the number of carbon atoms at the pinning points of water droplets was higher than that of others.