Molecular Dynamics Simulation of Compound Droplet Detachment Using Magnetic Attractive and Repulsive Forces

This paper investigates the interfacial forces controlling the detachment behavior of a multiphase droplet composed of immiscible liquids, an oil-coated water droplet, from a nonwetting surface, with special attention to the residue left on the surface after droplet detachment. In particular, the force required to detach a compound droplet from a spherical surface is simulated by using techniques of molecular dynamics (MD) simulations on atomistic scales. The resulting force and residual volume are then scaled up to predict the force of detachment obtained experimentally by cloaking a water droplet with an oil-based ferrofluid and detaching it from a coated glass bead by using a magnet. Using magnetic attraction and repulsion forces, it was found that a repulsive force can help reduce the amount of water residue on the surface. Good general agreement was observed between the predictions of our MD simulations and their experimental counterparts despite six orders of magnitude difference in size. The study presented in this paper can pave the way for developing a relationship between the volume of the residue on a surface and the force causing the detachment. Such information can benefit a variety of industrial applications involving multiphase droplets that interact with surfaces.