Nanoscale Insight into the Mechanism of a Highly Oriented Pyrolytic Graphite Edge Surface Wetting by "Interferencing"...

The new molecular dynamics simulation results showing the influence of the edge carbon surface atoms on the wettability of a highly oriented pyrolytic graphite (HOPG) surface with water nanodroplets are reported. The conditions for the occurrence of the Wenzel effect are discussed, and the Cassie-to-Wenzel transition (CTWT) mechanism in the nanoscale is explored. This transition is detected by the application of a new procedure showing that the CTWT point shifts toward larger values of carbon-oxygen potential well depth with the decrease in the HOPG side angle. It is concluded that the Wenzel effect significantly contributes to the contact angles (CAs) measured for the HOPG surfaces. The Wenzel effect is also very important for the "HOPG" structures possessing the disturbed C-C interlayer distance, and its influence on the water nanodroplet CAs is strongly pronounced. The structure of water confined inside slits and on a HOPG surface is studied using the analysis of the density profiles, the number of hydrogen bonds, and, modified for the purpose of this study, structure factor. The detailed analysis of all parameters describing confined water leads to the conclusion about the presence of characteristic interference patterns revealed as a result of long-term simulation. A simple model describing this effect is proposed as the starting point for further considerations.