Facultat de Física

Departament de Física de la Matèria Condensada

Active materials: strategies to understand collective motion

Pasquale Digregorio (pasquale.digregorio@uniba.it)

Postdoc Juan de la Cierva. Departament de Física de la Matèria Condensada. Universitat de Barcelona.

Active materials are systems of many units where single constituents can convert external energy into mechanical work.
Inspired to the behaviour of living agents, numerous theoretical models of active matter have been developed, where a steady energy input at the microscopic level breaks detailed balance and drives the system out of thermal equilibrium, in the absence of external driving.
Unbound from equilibrium, active matter displays a large variety of emergent collective behaviours. With the aim to give the sense of such diversity and richness, I will introduce two different models of active materials, designed in two different theoretical frameworks, that develop diverse collective motion.
The first one is a particle-based model of self-propelled particles, undergoing Motility-Induced Phase Separation. I will introduce this phenomenon and show novel findings about cluster formation and coarsening in the presence of activity-driven aggregation.
The second is a fluid dynamics model of nematic liquid crystals with local active stress. This system shows chaotic flows at small Reynolds numbers, that can be characterised by looking at the topological defects of the nematic field.
For both models and phenomena, I will describe what are the fundamental questions and the analytical approaches that we use to deal with them.