(62i) Formation Mechanisms for Microscopic Precursors in Droplet Spreading

Molecular precursor are ultrathin films that preced spreading droplets. While the mass transport mechanisms and dynamics of molecular precursors are known, what is necessary for precursors to form, and the reason why different kinds of precursors exist, remain unclear. Based on large-scale molecular dynamics simulations of a relatively simple molecular model, we demonstrate that as the interaction between the droplet and substrate becomes more favorably attractive, the spreading process passes through successive regimes with no precursor, a monolayer precursor, and a continuously growing precursor, respectively. We establish general guidelines governing both the nature of the spreading process as well as the shape of the precursor, when it exists.