Pratikshya Jena: Pattern Formation and Unconventional Phase Separation in Active Matter systems

Active matter consists of self-driven units that consume energy to generate motion, placing these systems fundamentally out of equilibrium. As a result, they exhibit emergent collective behaviors such as flocking, swarming, turbulence, and phase separation that are absent in equilibrium systems. In this seminar, I will discuss two projects:

• Spatio-temporal pattern formation in growing bacterial suspensions I will describe how growing bacterial colonies exhibit collective behavior driven by growth. We identify distinct dynamical phases named as dilute, turbulent, and heterogeneous and characterized through statistical and morphological measures, and show how colony growth induces transitions between these phases. (Scientific Reports, 15(1):30948, 2025. pages 21, 37)
• Unconventional phase separation and fractal interfaces of colloids in active liquids I will present a theoretical framework that extends passive Model B for colloids to include colored noise, for capturing the role of activity. This model predicts phase separation at very low densities, consistent with experiments on colloidal clusters in E. coli suspensions (conducted in collaboration). Remarkably, the order-parameter correlation function obeys dynamical scaling, but with a domain growth law of $t^{1/4}$, deviating from the classical Lifshitz–Slyozov $t^{1/3}$ scaling. We further show that the evolving interfaces show fractal morphologies, leading to unconventional coarsening dynamics. (arXiv:2508.11000, 2025. pages 22, 95, 102,105)