Pasquale Digregorio is a Postdoc at CECAM (Centre Européen de Calcul Atomique et Moléculaire) - EPFL. His current research activity focuses on the study of out-of-equilibrium active systems, ranging from particle-based models of self-propelled and self-spinning agents to fluid-dynamics models of active nematic liquid crystals, with particular interest in their critical behaviour, phase transition, collective structural and kinetic properties.
Tuesday April 18th
Active turbulence in nematic liquid crystals
Active materials are systems of many particles where single constituents consume energy from the environment and convert it into mechanical work. Active matter models are inspired by macroscopic living systems and biology, and their study is primarily aimed towards a theoretical understanding of collective phenomena like flocking, clustering and other types of self-organisation.
Within a living cell, motor proteins like kinesin are responsible for the transport of intracellular components. The functioning of this active transport is well known and it has been employed to build synthetic assemblies of microtubules, which are stirred at the level of the single components and evolve out of thermal equilibrium. The presence of molecular motors drives chaotic flow at the large scale, which resembles inertial turbulence and is therefore called active turbulence.
We use a model of nematic liquid crystals in the presence of a microscopic active stress to study this system. The onset of active chaotic flows leads to a sustained proliferation of topological defects that retain some unique properties compared with passive liquid crystals. We analyse the morphology and dynamics of these topological defects to deduce fundamental properties of active turbulence.