Droplet spreading driven by van der Waals force: a molecular dynamics study

Abstract

The dynamics of droplet spreading is investigated by molecular dynamics simulations fortwo immiscible fluids of equal density and viscosity. All the molecular interactions aremodeled by truncated Lennard-Jones potentials and a long-range van der Waals force isintroduced to act on the wetting fluid. By gradually increasing the coupling constant in theattractive van der Waals interaction between the wetting fluid and the substrate, weobserve a transition in the initial stage of spreading. There exists a critical value of thecoupling constant, above which the spreading is pioneered by a precursor film. Inparticular, the dynamically determined critical value quantitatively agrees with thatdetermined by the energy criterion that the spreading coefficient equals zero. Thelatter separates partial wetting from complete wetting. In the regime of completewetting, the radius of the spreading droplet varies with time as , a behavior also found in molecular dynamics simulations where the wetting dynamics isdriven by the short-range Lennard-Jones interaction between liquid and solid.