Molecular Dynamics Study of Binary Nanodroplet Evaporation on a Heated Homogeneous Substrate

The evaporation mechanism of miscible binary nanodroplets from heated homogeneous surfaces was studied by molecular dynamics simulations, which has never been studied before. The binary droplets contain a hydrophilic component (type-2 particles) and a hydrophobic component (type-3 particles). It is shown that liquid-liquid interaction strength (ε₂₃) and hydrophilic particle number fraction (φ) have great influence on the surface tension, wetting characteristics, evaporation patterns, evaporation rate, and local mass flux. It is observed that when ε₂₃ ≥ 1, or φ ≈ 0.5, the evaporation mode is the constant-contact-angle mode. Otherwise, it is the mixed mode. We found that the evaporation rate becomes faster when φ and ε₂₃ increase. The droplets become more hydrophilic when φ increases, which promotes heat transfer efficiency between the liquid-solid interface. Besides, a larger ε₂₃ promotes the heat transfer inside the droplet. The mass transfer to the vapor phase occurs preferentially in the vicinity of TPCL (three phase contact line) in the hydrophilic systems (θ < θ), where θ is the critical contact angle, while in most hydrophobic systems (θ > θ), the mass flux close to the TPCL is suppressed. We found that θ ∈ (102°-106°), which is different from the theoretical one, θ = 90°. The discrepancy is attributed to the existence of the adsorption layer near the TPCL.