Dissolutive wetting of Ag on Cu: A molecular dynamics simulation study

Reactive wetting in the eutectic AgCu system is studied with molecular dynamics simulations. As Ag(l) spreads on the Cu surface, Cu dissolves into the liquid. The results for reactive wetting are compared to simulations in which no mixing is permitted, demonstrating that wetting kinetics are enhanced by dissolution reactions. The time dependent radius of the droplet R(t) is used to quantify kinetics for the wetting geometry of an infinitely long cylinder spreading on a substrate. Data show that, when dissolution is dominant, spreading is well described by R(t) ∼ (R0t)1/2, where R0 is the starting cylinder radius. Contact angle θ(t) data were calculated via a method that accounts for structure near the contact region and compared to data obtained using circular fits to the droplet profile. Significant differences were observed due to molecular scale structure that rapidly evolves near the contact line. This structure exhibits markedly lower θ than what is predicted from droplet profile data and it is proposed to exist throughout most stages of dissolutive wetting. Simulations of AgCu binary liquids spreading on Cu demonstrate that wetting kinetics decrease with increasing Cu in the liquid, further emphasizing that wetting kinetics are intrinsically linked to dissolution kinetics. After dissolution is complete, a Ag-rich monolayer of atoms advances diffusively across the Cu surface.