Molecular dynamics simulation of microscopic droplet spread on rough surfaces

This study uses molecular dynamics simulations to elucidate the spreading behaviour of a liquid droplet oil a rough solid surface. The Lennard-Jones potential energy model is adopted as the interaction model between the liquid and the solid molecules. The paper considers two typos of rough surface: periodic and random. These surfaces are characterized by their roughness height and their spatial variation. For a periodic surface, the roughness height is defined by the amplitude, A, while for a random surface, it is defined in terms of the standard deviation of the roughness height, sigma. Regarding the spatial variation of the surface, a periodic surface is characterized by the wavelength, lambda, while the random surface is characterized by its autocorrelation length, L. Simulation results indicate that the characteristics of the rough surface can significantly influence spreading behaviour, in terms of final equilibrium time, spreading radius, and spreading topography. It is observed that the effects of roughness height and spatial variation are broadly similar for both periodic and random surfaces. It is found that increasing roughness height and decreasing spatial periodicity both prolong the final equilibrium time, and that the filial spreading radius decreases with increasing roughness height and increases with larger spatial periodicity.