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Molecular dynamics simulations of single water, water-methanol, or water-IPA (isopropyl-alcohol) mixture droplets on a solid surface were performed with various mixture ratios. An increase in alcohol fraction generally gave an increase in droplet wettability. Both methanol and IPA molecules showed a strong preference to gather at various interfaces, with methanol molecules also showing a tendency to diffuse into the droplet bulk. Specific interfacial tensions were investigated using quasi-one-dimensional simulation systems, and liquid-vapor and solid-liquid interfacial tensions were found to decrease greatly due to the presence of interfacial alcohol, while solid-vapor interfacial tensions were proved to have little influence on wettability. Young's relation was found to hold quantitatively well for both water-methanol and water-IPA droplets. The validity of using Bakker's equation on solid-liquid interfaces was also investigated, and it was shown that for tightly spaced crystal surfaces, the introduced uncertainly is small.

Molecular dynamics simulations of a nanoscale liquid droplet on a solid surface are carried out in order to examine the pressure tensor field around the multiphase interfaces, and to explore the validity of Young's equation. By applying the virial theorem to a hemicylindrical droplet consisting of argon molecules on a solid surface, two-dimensional distribution of the pressure tensor is obtained. Tensile principal pressure tangential to the interface is observed around the liquid-vapor transition layer, while both tensile and compressive principal pressure tangential to the interface exists around the solid-liquid transition layer due to the inhomogeneous density distribution. The two features intermix inside the overlap region between the transition layers at the contact line. The contact angle is evaluated by using a contour line of the maximum principal pressure difference. The interfacial tensions are calculated by using Bakker's equation and Young-Laplace equation to the pressure tensor distribution. The relation between measured contact angle and calculated interfacial tensions turns out to be consistent with Young's equation, which is known as the description of the force balance at the three-phase interface.

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