Facultat de Física

Departament de Física de la Matèria Condensada

From Chemical Dissipation to State Selection in Active Nematics

Dr. Andrés Arango-Restrepo

Department of Physics -- Faculty of Mathematics and Physics, University of Ljubljana

How does chemical energy drive collective motion, and how does it control transitions between nonequilibrium states? In this talk, I will address these questions within a unified mesoscopic nonequilibrium thermodynamic framework for confined active nematics. Starting from chemical free-energy consumption and entropy production, the framework connects chemo-mechanical energy conversion with active stresses and the resulting nematic dynamics. This provides a thermodynamic description of flows, spatial redistribution, and topological-defect dynamics in confined microtubule–motor systems, while recovering the conventional active-stress formulation as a limiting case. The same framework can then be coarse-grained at the level of the emergent defect configurations. Their dynamics are described through a master equation, where nonequilibrium transition rates quantify the creation and annihilation of defects and reveal how confinement biases the selection and persistence of particular dynamical states. Together, these results connect energy and entropy flows, continuous active dynamics, and stochastic transitions between collective states within a single thermodynamic picture of active nematics far from equilibrium.

Andrés Arango-Restrepo is a Colombian-Spanish researcher, chemical engineer, and PhD in Physics, specializing in nonequilibrium thermodynamics, statistical physics, active matter, and biophysics. He was initially trained at the National University of Colombia, where he studied Chemical Engineering and later completed a Master’s degree in Chemistry, conducting research on nonequilibrium thermodynamics and self-organization. He later completed his PhD in Physics at the University of Barcelona, where he developed a thermodynamic theory to describe the formation and selection of self-assembled structures out of equilibrium, with particular emphasis on the roles of dissipation and entropy production in their organization. His dissertation received the qualification of Excellent Cum Laude and was recognized with the Extraordinary Doctoral Thesis Award from the University of Barcelona. After his PhD, he extended this research toward active matter, studying active particles, spontaneous symmetry breaking, and transport and dissipation processes in systems driven out of equilibrium. He currently works at the University of Ljubljana, where he investigates active nematics and collective biological systems, seeking to establish connections between activity, dissipation, spatial organization, and state selection.