Active colloidal molecules and chains in inhomogeneous activity: effect of interactions, hydrodynamics, and confinement

• Applicant: Hossein Vahid Dastjerdi
• Subject Area: Statistical Physics, Nonlinear Dynamics, Complex Systems, Soft and Fluid Matter, Biological Physics
• Term: since 2025
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 561963765

Active matter systems, which harness energy from their surroundings to self-propel and operate far from equilibrium, have become central to understanding collective behaviors in both biological and synthetic contexts. Previous research has explored diverse phenomena in active matter, such as chemotaxis and anti-chemotaxis, where self-propelled particles migrate up or down chemical gradients, respectively. For instance, bacterial chemotaxis relies on motility along nutrient gradients, while artificial active Brownian particles (ABPs) exhibit anti-chemotaxis by accumulating in low-activity regions. This body of work has revealed how particle alignment and motility patterns in activity gradients affect clustering, with implications for understanding immune cell recruitment, cancer metastasis, and synthetic micro-swimmer applications. Recent studies have broadened this understanding by examining the influence of chain-like active polymers, particularly tangentially driven active polymers (TDAPs), which mimic biofilament behavior and display unique conformational transitions. These TDAPs demonstrate how structural properties, such as flexibility and propulsion forces, impact clustering and migration in active environments. For instance, the active matter group at IPF demonstrated that non-interacting ABPs can exhibit chemotaxis when attached to passive cargo. However, key questions remain about how factors such as steric effects, particle shape, interaction strength, and polymer architecture influence these transitions. This research proposal aims to investigate emergent chemotactic behaviors in active-passive mixtures. Primarily, I aim to address how interactions affect the collective behavior and chemotaxis of these systems. Additionally, hydrodynamic interactions will be studied, as they play a critical role in mediating movement, clustering, and collective dynamics both in bulk environments and when confined. Furthermore, interactions with substrates will be examined, as surface proximity can significantly alter active particle behavior by modifying interaction forces and particle orientation. Overall, this study aims to provide a comprehensive understanding of the factors driving chemotactic behavior in active matter systems across diverse environments.

• DFG Programme: WBP Position