The contact angle and structure of water on the graphite-like substrate: A classical density functional approach

The influences of temperature and water−graphite interaction energy on the contact angle (θ) and structure of water on the graphite-like substrate have been investigated using the classical density functional theory. We find that the temperature-dependent behavior of cosθ is contingent upon the water−graphite interaction energy, manifesting in three distinct patterns: increasing, decreasing, or remaining nearly invariant with temperature within the examined range (273.16–640K). Furthermore, a novel simple equation has been derived to describe the temperature-dependent variation of cosθ at constant water−graphite interaction energy, that is, $\partial \cos \theta /\partial T=\lambda /{\left({\gamma }^{\mathrm{lv}}\right)}^2$, where ${\gamma }^{\mathrm{lv}}$ is the water−vapor interfacial tension, and the value of $\lambda$ depends on the water−graphite interaction energy. According to different values of $\lambda$, this equation is able to successfully represent the three aforementioned patterns. At last, the density profile and hydrogen bonding structure of water near the substrate have been analyzed to offer microscopic insights.