Symmetry breaking propulsion of magnetic microspheres in nonlinearly viscoelastic fluids
Rogowski, Louis William
Wilking, James N.
Fu, Henry C.
Kim, Min Jun
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Microscale propulsion impacts a diverse array of fields ranging from biology and ecology to health applications, such as infection, fertility, drug delivery, and microsurgery. However, propulsion in such viscous drag-dominated fluid environments is highly constrained, with time-reversal and geometric symmetries ruling out entire classes of propulsion. Here, we report the spontaneous symmetry-breaking propulsion of rotating spherical microparticles within non-Newtonian fluids. While symmetry analysis suggests that propulsion is not possible along the fore-aft directions, we demonstrate the existence of two equal and opposite propulsion states along the sphere’s rotation axis. We propose and experimentally corroborate a propulsion mechanism for these spherical microparticles, the simplest microswimmers to date, arising from nonlinear viscoelastic effects in rotating flows similar to the rod-climbing effect. Similar possibilities of spontaneous symmetry-breaking could be used to circumvent other restrictions on propulsion, revising notions of microrobotic design and control, drug delivery, microscale pumping, and locomotion of microorganisms.
Rogowski, L.W., Ali, J., Zhang, X. et al. Symmetry breaking propulsion of magnetic microspheres in nonlinearly viscoelastic fluids. Nat Commun 12, 1116 (2021). https://doi.org/10.1038/s41467-021-21322-0