ABSTRACT
The Marangoni effect, induced by the surface tension gradient resulting from the gradient of temperature, concentration, or electric potential gradient along a surface, is commonly utilized to manipulate a droplet. It is also the reason for unique behaviors of liquid metal such as moving, breathing, and large-scale deformation under an electric field, which have aroused tremendous interest in academics. However, liquid metal droplets are usually treated as solid marbles, which neglect their fluidic features and can hardly explain some unusual phenomena, such as a droplet under a stationary electric field that moves in the opposite direction in different solutions. To better clarify these discrepancies, this study reveals that the movement of liquid metal is directly driven by viscous forces of solution rather than interfacial tension. This mechanism was determined by analyzing flow characteristics on a liquid metal surface. Additionally, experiments with liquid metal free falling in solution, liquid metal droplet movement experiments on substrates with different roughness, and liquid metal droplet movement experiments under high current density were additionally conducted to verify the theoretical interpretation. This research is instrumental for a greater understanding of the movement of liquid metal under an electric field and lays the foundation for the applications of liquid metal droplets in pumping, fluid mixing, and many other microfluidic fields.
ABSTRACT
The Marangoni flow of room temperature liquid metal has recently attracted significant attention in developing advanced flexible drivers. However, most of its induction methods are limited to an external electric field. This study disclosed a new Marangoni flow phenomenon of liquid gallium induced by the gallium-copper galvanic corrosion couple. To better understand this effect, the flow field distribution of liquid gallium was modeled and quantitatively calculated. Then, the intrinsic mechanism of this flow phenomenon was interpreted, during which natural convection and temperature gradient were both excluded and the galvanic corrosion couple was identified as the main reason. In addition, this conclusion was further confirmed by combining the experimental measurement of liquid gallium surface potential and the thermocapillary effect. Moreover, the temperature condition was found to be an indirect factor to the Marangoni flow. This finding broadens the classical understanding of liquid metal surface flow, which also suggests a new way for the application of soft machines.
