Mechanisms and requirements for three-dimensional colloidal odd viscosity

Determine experimentally realizable three-dimensional colloidal systems exhibiting odd viscosity, and characterize the microscopic mechanisms and minimum fluidic requirements underlying the emergence of odd viscosity.

Background

The paper proposes active surfaces with parity-violating odd slip as a route toward metafluids exhibiting odd viscosity. It demonstrates theoretically that dilute suspensions of particles with pseudo-vectorial odd slip, or of aligned conical particles with pseudo-scalar odd slip, can generate odd-viscous responses.

Despite these theoretical constructions, the authors identify unresolved foundational issues concerning the experimental realization of odd viscosity in three-dimensional colloidal systems, as well as the microscopic origin and minimal environmental conditions required for that response. These issues motivate further experimental and theoretical work beyond the specific odd-slip models analyzed in the paper.