Hydrodynamics experiments with ferromagnetic liquid droplets*

Structured functional liquids combine mechanical versatility of fluids with solid-state properties, such as ferromagnetism, and offer a route to synthesize and control magnetic liquids for adaptive liquid robotics. Studies on these intriguing materials are only in their nascent state [1,2], and a profound understanding of the physical state is still lacking. We use hydrodynamics experiments to probe how the magnetization of ferromagnetic liquid droplets, governed by the assembly and jamming of magnetic nanoparticles at liquid-liquid interfaces, and their response to external stimuli can be tuned by chemical, structural and magnetic means. These results are augmented by structural analysis of short-range ordered nanoparticle assemblies, and numerical modeling of the forced rotational motion. Our results highlight the leading role of structural short-range order and nanoparticle jamming on magnetic properties, which provide a path toward nano patterning structured liquids.

[1] X. Liu, et al., Science 365, 264 (2019).
[2] R. Streubel, X. Liu, X. Wu, T.P. Russell, Materials 13, 2712 (2020).