Spreading Kinetics of Ultrathin Liquid Films Using Molecular Dynamics

Ultrathin liquid films play a critical role in numerous engineering applications. Although crucial to the design and application of ultrathin liquid films, the physical mechanisms that govern spreading on the molecular scale are not well-understood, and disagreement among experiments, simulations, and theory remains. We use molecular dynamics simulations to quantify the speed at which the edge of a polymer droplet advances on a flat substrate as a function of various environmental and design parameters. We explain the physical mechanisms that drive and inhibit spreading, identify different spreading regimes, and clarify transitions between spreading regimes. We demonstrate that the edge of a droplet spreads according to a power law with two distinct regimes, which we attribute to competing physical mechanisms: a pressure difference in the liquid droplet and molecule entanglement. This research unifies many years of liquid spreading research and has implications for systems that involve designing complex ultrathin liquid films.