报告主题：Shaping active matter: Symmetry, confinement, and effective interactions

主 讲 人：Ignacio Pagonabarraga 教授（巴塞罗那大学）

主 持 人：高永祥

时 间：2026年7月2日（四）15：00

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 matter systems, composed of self-driven entities that continuously consume energy to generate motion or mechanical stresses, represent a fundamental departure from the principles of equilibrium statistical mechanics. Their collective behavior arises from a complex interplay between direct interactions, hydrodynamic couplings, and the self-consistent evolution of the medium in which they are embedded. Understanding the mechanisms underlying pattern formation, self-assembly, and emergent order in these systems poses profound theoretical and conceptual challenges for nonequilibrium physics.

I will discuss the role of symmetry and confinement in the effective interactions that govern the organization of active systems across scales. Using minimal dynamical models, I will show that the symmetry of self-propulsion plays a decisive role in the nature of emergent structures in suspensions of self-propelled particles and in complex environments.

I will further address the role of soft confinement, such as droplets, vesicles, and phase-separating mixtures, in shaping the collective behavior of active particles. Active stresses within such environments compete with interfacial tension and other restoring forces, giving rise to enhanced interfacial fluctuations, dynamic morphologies, and, in some regimes, the stabilization of active emulsions with well-defined length scales. These phenomena illustrate how activity can arrest coarsening, control morphology, and promote the coexistence of nonequilibrium steady states.

Taken together, these results highlight how fundamental symmetry considerations and mechanical constraints can be used to rationalize and predict the emergent organization of active systems. They also point toward a unified framework for understanding the self-organization of active materials—biological or synthetic—through the balance of internal activity, confinement, and effective interactions.