Asymmetric and symmetric spreading for a nanodroplet on an isothermally heated surface in the presence of a parallel electric field.

Under parallel electric fields and free evaporation conditions, the statics and dynamics of spreading–evaporating nanodroplets are investigated on an isothermally heated surface via molecular dynamics (MD) simulations. The simulation results show that at the substrate temperature of Ts = 320 K, the static and dynamic contact angles on the left and right edges are initially asymmetric and then symmetric with increasing field strengths of E = 0.00–0.06 V Å−1, resulting in the asymmetric-to-symmetric spreading transition of spreading–evaporating nanodroplets. Under weak evaporation condition, that is, at Ts = 320 K, the asymmetric-to-symmetric spreading transition is triggered by enhancing the intrinsic surface wettability θ0 = 49°–80° at a constant field strength of E = 0.03 V Å−1. However, at the substrate temperature of Ts = 350 K, the symmetric-to-asymmetric spreading transition first appears for the static and dynamic contact angles on the left and right edges, and then the asymmetric-to-symmetric spreading transition appears with increasing field strength. Under strong evaporation condition, that is, at Ts = 350 K, as the field strength is constant at E = 0.03 V Å−1, the asymmetric-to-symmetric spreading transition also appears with increasing surface wettability. [ABSTRACT FROM AUTHOR]