(5h) Microscopic Origins of Novel Transport Properties in Active Fluids

Active fluids, which are composed of self-propelled particles, are known to exhibit novel transport properties. Familiar linear laws such as those of Fourier, Fick, and Newton -- describing the constitutive behavior of heat, mass, and momentum transport, respectively -- must be revisited in this context. In particular, the breaking of time reversal symmetry at the particle scale can dramatically affect transport at the continuum scale. One example is the so-called odd viscosity, appearing in two dimensional chiral active fluids. Recent theoretical work by Epstein and Mandadapu [1] has obtained Green-Kubo relations for the full set of viscosity coefficients in such active fluids, in which odd viscosity emerges as a direct consequence of time reversal symmetry breaking at the level of stress fluctuations. In this talk, we present the results of simulations of a two-dimensional fluid composed of self-rotating active dumbbell particles, finding the viscosities computed using the newly obtained Green-Kubo relations to be in good agreement with values measured independently from shear flow simulations [2]. This agreement lends support to the broader application of non-equilibrium thermodynamics concepts, in particular the Onsager regression hypothesis, in the context of non-equilibrium steady states of active fluids.