Taiji Patterns Swirled Out of Magnetic Liquid Metal Fluids under Rotating Magnets

Abstract

While magnetic fluids are well known for their rich ferrohydrodynamic behaviors, prior researches on dynamic droplet morphologies have largely been confined to the nonconducting matters. From an alternative, the electrically conductive magnetic liquid metals offer ever larger space for explorations meanwhile also incubate intriguing mysteries that had not been understood before. Here, we disclosed a group of rather profound fluidic phenomena happening on the magnetic liquid metals with sizes spanning from millimeter to centimeter scales when subject to the impact of a rotating magnet pair. We conceived that the identified flow patterns highly resemble that of the Chinese Taiji diagrams widely known as a classical theory to describe all things genesis and transformation, indicating the kaleidoscopic variations and intrinsic clues between modern magnetic liquid metal physics and the nature rules lying behind the ancient Eastern philosophy. Through systematically tuning the droplet volume, magnetic field strength, and magnet rotational speed, we achieved precise control over the liquid metal fluidic morphologies such as ellipses, dumbbells, toroidal rings, and Yin-Yang symbols, and quantified their dependence on the prescribed experimental conditions. Following the routes to construct the Taiji eight diagrams and their derivatives, we classified the disclosed flow patterns into eight representative schemes and three phase diagrams were plotted to characterize the fluidic patterns of the magnetic droplets correspondingly. The underlying mechanisms of magnetic liquid metal flow separation and coalescence were further interpreted from an energy perspective. These findings suggest enormous experimental insights and a theoretical framework for advancing fundamental magnetohydrodynamics and related engineering practices.