Lorentz-force driven rotation and interface modulation of liquid metal

The liquid metal subjected to a circumferential Lorentz force exhibits sustained rotation. We experimentally investigate how the rotational dynamics of the liquid metal are affected by the presence or absence of a NaOH aqueous layer and the magnitude of the applied current that causes electromagnetic drive, with a particular focus on interfacial deformation. We used a circular flat assembly with alternating ring electrodes and magnets to generate the circumferential Lorentz force. As the current increases, the interface of the liquid metal slug evolves from a mildly concave morphology to a toroidal form, and distinct rotation modes appear within the toroidal state. Using the force balance that accounts for the electromagnetic body force, centrifugal force, gravitational force, and interfacial tension force, we identify a set of governing dimensionless parameters that characterize the morphological variations of the liquid metal. Furthermore, we discuss how the interface tuning by Lorentz‑driven rotation can be exploited in engineering systems, such as adaptive liquid metal mirrors designed for high heat flux and other extreme environments.