报告主题：Symmetry Breaking and Collective Motion in Chemically Active Colloids

主 讲 人：Ignacio Pagonabarraga 教授（巴塞罗纳大学）

主 持 人：高永祥

时 间：2026年11月9日（一）10：00

地 点：致知楼706

嘉宾简介：

Ignacio Pagonabarraga studied at the University of Barcelona (UB) where he obtained his PhD in Physics in nonequilibrium statistical physics in 1996. He performed postdoctoral stays at Instituut Amolf (Amsterdam, the Netherlands) and University of Edinburgh (Scotland, UK) and moved back to Barcelona. He is Professor of Physics at the Department of Condensed Matter Physics in UB since 2011. He has been the CECAM Director, with headquarters in the EPFL (Lasuanne, Switzerland) in the period 2017-2022 and is the Director of the Institute of Complex Systems at UB (UBICS) since 2024. His research focuses on the theoretical understanding of soft matter systems out of equilibrium, with particular interest in collective phenomena in active matter, aiming at reaching fundamental new understanding of the mechanics and emerging behavior in such systems. He develops and exploits novel computational methods to study these complex, heterogeneous dynamic systems.

报告摘要：

Active colloids are self-driven particles that continuously consume energy to generate motion and mechanical stresses. Their collective behavior is governed not only by microscopic interactions, but also by the symmetry of self-propulsion, hydrodynamic couplings and the constraints imposed by their environment. Understanding how these ingredients combine to generate collective structures and emergent organization is a central challenge in nonequilibrium physics.

In this talk, I will discuss how symmetry and confinement shape the effective interactions governing active colloidal systems. Using minimal dynamical models, I will show how the symmetry of self-propulsion determines collective organization in suspensions of active particles, particularly in the presence of obstacles and complex environments. These examples illustrate how the collective response of active colloids can differ substantially from what would be expected from their microscopic interactions alone.

I will then explore how soft confinement, provided by droplets, vesicles and phase-separating mixtures, modifies the collective behavior of active particles. In these systems, active stresses compete with interfacial tension and other restoring forces, leading to enhanced interfacial fluctuations, dynamic morphologies and, under suitable conditions, the stabilization of active emulsions with well-defined length scales. These mechanisms reveal how activity can arrest coarsening and control the morphology and organization of complex colloidal systems.

Together, these results illustrate how symmetry and mechanical constraints provide fundamental principles for understanding the emergence and control of collective structures in active colloids.