Abstract
Active suspensions consist of self-driven particles that continuously convert energy into motion and mechanical stresses. Unlike passive colloidal systems, their collective dynamics is governed not only by direct particle interactions, but also by interactions mediated by the surrounding medium. Chemical concentration fields and hydrodynamic flows can generate long-ranged and collective couplings, whose nature depends on particle symmetry, the properties of the surrounding fluid and the geometry of the environment. Understanding how these interactions combine to generate emergent collective behavior is a central challenge in nonequilibrium physics.
In this talk, I will explore how mediated interactions and environmental constraints shape the collective dynamics of active suspensions. I will first discuss how chemical and hydrodynamic couplings, together with the symmetry of self-propulsion, determine the effective interactions and collective response of active particles, particularly in complex and confined environments. I will then consider heterogeneous media, such as phase-separating binary mixtures, where the coupling between active particles and the evolving composition and morphology of the surrounding fluid can lead to interfacial instabilities, arrested phase separation and the emergence of dynamically stabilized structures, including active emulsions.
Finally, I will discuss how the coupling between catalytic activity and light sensitivity provides a route to dynamically control active suspensions. By using spatially and temporally structured illumination to modulate catalytic activity, heterogeneous activity landscapes can be generated and used to explore and control collective dynamics in active systems.
Together, these examples illustrate how chemical and hydrodynamic interactions, confinement and environmental heterogeneity provide complementary routes to generating and controlling emergent behavior in active suspensions.