Experimental study on impact dynamics of droplet on heated copper surfaces and liquid gallium surfaces

Abstract

The research on droplet impact has always focused on rigid solid surfaces. In the past two decades, the study of droplet impact dynamics on soft substrates, represented by PDMS, has received increasing attention, mainly driven by the development of flexible electronic technology. However, research on the dynamics of droplet impact on liquid metal surfaces is still relatively insufficient. Compared with PDMS, liquid metals exhibit higher surface tension and lower viscoelasticity, indicating that their droplet impact dynamic behavior will be significantly different. This paper reports the experiments for ethanol droplets impact heated copper surfaces and liquid gallium surfaces, and the effects of the Weber number (We) and surface temperature were analyzed. The results show that the patterns of droplet impact heated copper surfaces and liquid gallium surfaces can be divided into reflection rebound, central jetting, rebound rotation, jetting with horizontal splashing, and breakup. The impact dynamics of droplets on copper surfaces mainly depend on We, while the impact dynamics of droplets on liquid gallium surfaces are related to both We and surface temperature. As the surface temperature of liquid gallium increases, droplet rotation and splashing are suppressed, and the droplet maximum spreading diameter D_max decreases. A semi-empirical model for the maximum spreading diameter of droplets was established by introducing surface temperature correction to consider energy dissipation caused by surface deformation and viscoelasticity. The research results contribute to understanding the influences of surface deformation and viscoelasticity on droplet dynamics.