Activity induced isotropic-polar transition in active liquid crystals

Abstract

Active fluids are intrinsically out-of-equilibrium systems due to the internal energy injection of the active constituents. We show here that a transition from a motion-less isotropic state towards a flowing polar one can be possibly driven by the sole active injection through the action of polarhydrodynamic interactions in absence of an ad hoc free-energy which favors the development of an ordered phase. In particular, we propose an analytical argument and we perform lattice Boltzmann simulations where the appearance of large temporal fluctuations in the polar fraction of the system is observed at the transition point. Moreover, we make use of a scale-to-scale analysis to unveil the energy transfer mechanism, proving that elastic absorption plays a relevant role in the overall dynamics of the system, contrary to what reported in previous works on the usual active gel theory where this term could be factually neglected.

Rheology of active emulsions with negative effective viscosity

“…Therefore, in absence of a Newtonian background, one would obtain an uniform liquid crystalline suspension whose rheological properties are well known in literature, both for passive and active preparations . [39][40][41] In the following section we will present the dynamical model and the numerical approach, while in Section 3 the observed rheological regimes will be discussed and classified. In particular, by systematically varying both the rate of active injection and the external forcing, we will show that a series of morphological and rheological transitions takes place, resulting in the development of both negative effective viscosity states and inviscid regimes, as well as shear thickening.…”

Rheology of active emulsions with negative effective viscosity

“…Importantly, the two components have the same nominal viscosity, so that the observed rheological behaviors uniquely result from the complexity introduced by the mutual effect of interfaces, liquid crystalline phase and activity. Therefore, in absence of a Newtonian background, one would obtain an uniform liquid crystalline suspension whose rheological properties are well known in literature, both for passive and active preparations [39][40][41].…”