Spontaneous Propulsion of Water Nanodroplet Induced by Wettability Gradient: A Molecular Dynamics Simulation Study
The directional propulsion of liquid droplet at nanoscale is quite an interesting topic of research in the fields of micro/nano-fluidics, water filtration, precision medicine and cooling of electronics. In this study, a unidirectional spontaneous transport of water nanodroplet on a solid surface with multi-gradient surface (MGS) inspired by natural species is modeled and analyzed by using Molecular Dynamics (MD) simulations. There are three different MGS considered in this study which contain different wedge angle of the hydrophilic region of the solid surface. The MGS contains two regions, a hydrophilic wedge shaped region with constant surface energy parameter equals to 50meV and a hydrophobic region with tuned surface energy parameter. The energy parameter of the hydrophobic region is set equal to (1meV, 5meV, 10meV, 20meV, 30meV, and 40meV) in order to alter the intensity of wettability gradient of the two surfaces and its effect on the propulsion of water nanodroplet is analyzed. Furthermore, three different size of water droplet containing 6000, 8000, and 10,000 water molecules are also used in this study and their effect of the transport behavior of water nanodroplet is also measured. Moreover, two different designs on solid surface with continuous wettability gradient are modelled and the impact of solid surface geometry on transport of water droplet is calculated by means of mean square displacement (MSD) and average velocity data. In addition, wedge shaped surface is found to be more superior for spontaneous propulsion of water droplet as compared to the parallel shape surface.