Nano water droplets, Quartz sand, Silica, Wettability, Contact angle, Molecular dynamics, Materials of engineering and construction. Mechanics of materials, TA401-492

The wettability mechanism of soil–water interfaces is of significant importance in geotechnical engineering. However, the effect of different contact angles on unsaturated sand soil behavior has been less understood. In this study, the wetting behavior of nano water droplets on various silica substrates is investigated using molecular dynamics. Seventeen groups of simulation systems with different interaction potential energies ($\varepsilon _{\mathrm{Si}} = 0.008$, 0.04, 0.2, 0.4, 0.6, 0.8, 1, 2 kcal/mol) and temperatures ($T = 273$, 298, 323, 353 K) are conducted. The results show that the contact angles varies intensively with interaction potential energies from 108.5° to 18.1°, which indicates a transition from hydrophobic to hydrophilic and wettability enhancement along with the increase of interaction potential energy. Simulation results also show that contact angles increase with the increase of temperature, whatever the hydrophobic or hydrophilic of the silica surface. Such phenomena are interpreted from the perspective of microstructure, along with the performance of macrostructure. In addition, results show that the contact angles are independent of the thickness and width (length) of silica substrate.