Conventional liquid droplets impacting a rigid surface spread and retract in a symmetric pattern. However, introducing odd viscosity—a non-dissipative, parity-violating transport property characteristic of chiral fluids—allows droplets to self-regulate their own mechanics upon impact. When impacting a superhydrophobic surface, these “odd droplets” break lateral symmetry, producing asymmetric deformations, internal rotation, directional bouncing, or rolling motion without needing external forces or microstructured surfaces.
Odd viscosity generates a reactive stress tensor orthogonal to local deformation rates, directly coupling internal vorticity gradients to momentum. During impact, wall shear forces trigger a non-uniform odd force field that shifts the droplet sideways and suppresses spreading. Reversing internal shear during retraction then alters these forces, spinning the droplet and converting translational kinetic energy into solid-body rotation.
Odd viscosity generates a reactive stress tensor orthogonal to local deformation rates, directly coupling internal vorticity gradients to momentum. During impact, wall shear forces trigger a non-uniform odd force field that shifts the droplet sideways and suppresses spreading. Reversing internal shear during retraction then alters these forces, spinning the droplet and converting translational kinetic energy into solid-body rotation.
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