Chandrasekhar Hall

Glass transition in dense systems of self-propelled particles

Chandan Dasgupta

IISC, Bangalore

In several biological systems, such as bacterial cytoplasm,
cytoskeleton-motor complexes and cell nuclei,self-propulsion or activity is found to fluidize a glassy state that exhibits characteristic glassy features in the absence of activity.To develop a theoretical understanding of this activity-induced non-equilibrium glass transition, we have studied, using molecular dynamics and
Brownian dynamics simulations, the effects of activity in two model glass forming liquids: the Kob-Andersen binary mixture in three dimensions and a two-dimensional system of two kinds of dumbbells. Activity is introduced by assuming that some of the particles experience a random active force.

We find that the introduction of activity dramatically reduces the glass transition temperature and the glass transition disappears beyond a threshold value of the activity. Some of the effects of
activity on the dynamics in the liquid state are determined by an "active temperature" that adds to the bath temperature. However, several properties of the "active" supercooled liquid obtained as the glass transition is approached by reducing the activity at a low
temperature, are found to be qualitatively different from those of the "thermal" supercooled liquid obtained as the glass transition is
approached by lowering the temperature at low activity. We present simple analytic arguments, based on a heuristic Langevin description of the dynamics of a particle in the cage formed by its neighbors,
which provide a rationalization of some of the features of the
dynamics observed in our simulations.