From spreading to splashing: Interfacial phenomena of an ethanol droplet impacts on ultracold surfaces

Understanding droplet impact behavior under low-temperature conditions is important for a range of fluid–surface interaction scenarios. This study explores the impact dynamics of ethanol droplets on hydrophilic silicon surfaces across a range of impact heights and sub-zero surface temperatures. Increasing impact height and decreasing surface temperature were found to influence the transition from spreading to splashing, with fingering frequently appearing as an intermediate morphology. Dimensionless parameters - including the Weber, Reynolds, and Capillary numbers - were calculated using temperature-dependent fluid properties. Existing criteria describing impact regime transitions were referenced and adapted to the present experimental system. To incorporate the influence of fluid volatility and interfacial cooling, a modified correlation was proposed by combining temperature-corrected Weber and Reynolds numbers with the Péclet number. The resulting criterion reflects the observed transition trends and may serve as a practical tool for analyzing droplet impact behavior of volatile fluids under sub-zero conditions.