Materials Research Science and Engineering Center

Jianshuo Qiu

“Emergent Structures in Dense Active Fluids”

Jianshuo Qiu*, Elias Putzig, Aparna Baskaran
Brandeis / Mathematics, Physics
Hosted by Baskaran's Lab

Abstract

Conventional fluid materials are composed of inanimate building blocks. Much current research deals with active fluids, which are composed of self-propelled particles and carry significantly different properties, such as energy consumption and collective motility. In this research, we study the emergent structures in active fluids at high densities in two dimensions. We hypothesize that at high densities, the emergent structures are composed of multiple asters with no disordered region between any two asters.

The research is implemented through both numerical and analytical methods. In the numerical method, a FTCS (Forward-Time Central-Space) scheme is used to write the code and to numerically solve the dynamical equations that describe the density and the polarization density of the self-propelled particles. Codes are run on the High Performance Computing Cluster, with different values of parameters called the particle propulsion speed and the inter-particle interaction parameter. The results are used to make plots of the density and the polarization density. The emergent structures are then identified from the plots. In the analytic method, called linear stability analysis, the nonlinear dynamical equations are approximated as linear equations around the homogeneous steady state solution to the dynamical equations. The conditions when this state becomes unstable are obtained and used to explain the emergent structures found. Finally, we find the structure composed of multiple asters with some disordered region between them, and the empirical relations between aster number, aster radius and parameters are obtained. Other new structures, such as streams, and extended single aster are also found. An empirical phase diagram of the distribution of different structure in the parameter space is plotted.

In future research, the reason why disordered region appears between multiple asters needs to be explained and other new emergent structures will be further studied.

Support

SMURF (Summer MRSEC Undergrad Research Fellowship)