Impact Dynamics of Oxidized Galinstan Droplets on Rough and Heated Substrates

Abstract Liquid-metal droplet impact plays a key role in thermal management, coating, and additive manufacturing, yet its dynamics on rough and heated surfaces remain to be elucidated. This study experimentally investigates the impact of oxidized Galinstan droplets on solid substrates, isolating the effects of surface roughness and substrate temperature in the absence of solidification. Experiments were conducted over wide ranges of Weber number (0.15 ≤ We ≤ 720), average surface roughness (0.2 nm ≤ Ra ≤ 19.5 μm), and surface temperature (25 °C ≤ Ts ≤ 400 °C). Our results show that surface roughness promotes splashing by reducing the critical impact velocity. By fitting the experimental data within the explored parameter range, an empirical splashing threshold, ReOh4/5 = 9.8r–0.28, is established by incorporating the dimensionless roughness (r), Reynolds number (Re), and Ohnesorge number (Oh). Despite its strong influence on splashing, surface roughness has a negligible effect on the maximum spreading factor (βmax) due to Galinstan’s high surface tension. Substrate temperature likewise exerts only a minor influence, as the droplet temperature variation during spreading causes only minor changes in the liquid properties and subsequent impact dynamics under our conditions. For all Ts and Ra conditions, the experimental data of βmax collapse onto an empirical correlation, βmax = 0.1(2154 + We/Oh)0.3 for Oh∼O(10−4) and 0.15 ≤ We ≤ 720.