Splashing of viscous droplets on heated surfaces

The splashing dynamics of low-viscosity droplets impinging on heated surfaces has been extensively studied. For high-viscosity droplets, however, the roles of viscosity and surface temperature in droplet splash are unknown. In this work, we investigate droplet splashing on heated surfaces through experiments and theoretical analyses. Specifically, the critical Weber numbers (\(We\)), \(W{e}_{C}\), for droplet splash are obtained through experiments for a wide range of surface temperatures, \({T}_{S}\), and Ohnesorge numbers. It is found that the thermal stabilization effect, i.e., droplet splash is suppressed by a heated surface, for low-viscosity droplets also holds for droplets with high viscosity. However, the thermal stabilization effect becomes less sensitive to surface temperature for high-viscosity droplets. Furthermore, the dual roles of viscosity in droplet splash, i.e., low-viscosity droplets promote splash, while high-viscosity droplets impede splash when viscosity increases, are found to be independent of surface temperature. Theoretical analysis reveals that thermal stabilization arises from gas-phase aerodynamics and lubrication effects, while the dual roles of viscosity are due to the competition between capillary stabilization and viscous damping. The findings in this work provide useful information for controlling droplet splashing in various applications, such as thermal spray coating and additive manufacturing.