Chaotic and periodical dynamics of active chiral droplets

The interplay between the chirality of many biological molecules and the energy injected at small length-scales as the result of biological processes is at the base of the life of the cells. With the aim of unveiling the connection between these two features, here we analyze by means of lattice Boltzmann simulations the behavior of an active droplet of cholesteric liquid crystal under the effect of intense active doping, within the framework of active gel theory. We find that a droplet of chiral liquid crystal, fueled by active force dipoles, develops defect loops (closed disclination lines) that pierce the interior of the droplet, leading the droplet to develop an erratic motility mode. When the droplet is fueled by in-warding active torque dipoles, three different dynamical regimes develops at varying both the thermodynamic chirality and the strength of active energy injection: a stable rotational state at low activity, an intermittent disclination dance regime, and a turbulent state where closed disclination lines formation is inhibited and new pairs of oppositely charged surface defects leads to the development of chaotic rotational motion. Finally, we show that out-warding torque dipoles are able to sustain a periodical dynamics at higher chirality characterized by the nucleation/annihilation of pairs of disclination rings. (C) 2020 Elsevier B.V. All rights reserved.