Dynamical cluster formation of colloids in bacterial bath

Abstract

Non-equilibrium systems have shown lots of intriguing behavior. Dynamic cluster formation of colloids due to presence of activity in the system is one such example. We here study 2D dynamical cluster of non-Brownian colloidal beads by varying bacterial density and colloidal beads density and compare them with Brownian beads by taking their images. We have motile bacteria of length nearly 3-micron and 0.25-micron diameter of cross-section and Polystyrene beads of size 7 micron. We are trying to see how clustering of beads is happening and whether there is any phase separation taking place or no. We observed dynamic clusters whose size was increasing with increasing bacterial concentration and area fraction. However, we do not see the size of cluster increasing with time for various bacterial concentration till area fraction of 0.45. In addition, we also looked for number fluctuation and we got log-log slope of standard deviation to mean number of particles to be greater than 0.5 but below 1, which is a characteristic of active systems