by Prof. Snigdha Thakur, IISER Bhopal

Abstract:

Active matter systems are characterized by the continuous conversion of chemical or other forms of energy into mechanical motion, driving them far from equilibrium. Chemical gradients, in particular, play a central role in the movement of both living and synthetic active systems. In this colloquium, I will discuss two classes of active matter - colloids and polymers - that exhibit rich dynamics such as self-propulsion, self-aggregation, and phase separation in response to chemical cues.

While self-propelling chemical motors are often realized through Janus particles with asymmetric catalyst distributions, I will show that even simple isotropic colloids can spontaneously assemble into dimer motors that self-propel. Collections of such colloids exhibit phase separation akin to a vapor–liquid transition. Extending beyond particle-like systems, we will also explore line-like active elements, such as ring polymers, where activity is distributed along their contour and competes with long-range interactions. Our results highlight how polar activity can swell shorter rings but crumple larger ones, while long-range attraction drives systematic collapse. Furthermore, we will discuss how shear flow impacts polar active filaments, with implications for understanding molecular machines that move along biopolymers such as chromatin. We propose that studying looped chromatin under shear flow may help classify the distinct modes of action of these molecular machines.