The odd free surface flows of a colloidal chiral fluid

• Published in: Nature physics Vol. 15; no. 11; pp. 1188 - 1194
• Main Authors: Soni, Vishal, Bililign, Ephraim S., Magkiriadou, Sofia, Sacanna, Stefano, Bartolo, Denis, Shelley, Michael J., Irvine, William T. M.
• Format: Journal Article
• Language: English
• Published: London Nature Publishing Group UK 01.11.2019; Nature Publishing Group; Nature Publishing Group [2005-....]
• Subjects: 639/301/923/614; 639/766/189; Atomic; Classical and Continuum Physics; Complex Systems; Computational fluid dynamics; Condensed Matter Physics; Fluid flow; Fluid mechanics; Fluids; Free surfaces; Hydrodynamics; Magnets; Mathematical and Computational Physics; Molecular; Optical and Plasma Physics; Physics; Physics and Astronomy; Surface dynamics; Surface waves; Theoretical
• ISSN: 1745-2473; 1745-2481
• DOI: 10.1038/s41567-019-0603-8

In simple fluids, such as water, invariance under parity and time-reversal symmetry imposes that the rotation of constituent ‘atoms’ is determined by the flow and that viscous stresses damp motion. Activation of the rotational degrees of freedom of a fluid by spinning its atomic building blocks breaks these constraints and has thus been the subject of fundamental theoretical interest across classical and quantum fluids. However, the creation of a model liquid that isolates chiral hydrodynamic phenomena has remained experimentally elusive. Here, we report the creation of a cohesive two-dimensional chiral liquid consisting of millions of spinning colloidal magnets and study its flows. We find that dissipative viscous ‘edge-pumping’ is a key and general mechanism of chiral hydrodynamics, driving unidirectional surface waves and instabilities, with no counterpart in conventional fluids. Spectral measurements of the chiral surface dynamics suggest the presence of Hall viscosity, an experimentally elusive property of chiral fluids. Precise measurements and comparison with theory demonstrate excellent agreement with a minimal chiral hydrodynamic model, paving the way for the exploration of chiral hydrodynamics in experiment. A chiral fluid comprising spinning colloidal magnets exhibits macroscopic dynamics reminiscent of the free surface flows of Newtonian fluids, together with unique features suggestive of Hall—or odd—viscosity.