Regensburg 2019 – wissenschaftliches Programm

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DY: Fachverband Dynamik und Statistische Physik

DY 38: Microswimmers (joint session DY/CPP)

DY 38.1: Vortrag

Mittwoch, 3. April 2019, 15:30–15:45, H19

Orientational ordering and collective motion in (semi-)dilute suspensions of active microswimmers — Christian Hoell, Giorgio Pessot, Hartmut Löwen, and •Andreas M. Menzel — Heinrich-Heine-Universität Düsseldorf, Düsseldorf, Germany

Polar orientational ordering in crowds of self-propelled particles is connected to the emergence of collective motion. We study orientational ordering in suspensions of active microswimmers. These objects propel by setting the surrounding fluid into motion. Since we focus on (semi-) dilute suspensions, such hydrodynamic effects dominate the swimmer interactions. For simplicity, we concentrate on planar arrangements of so-called pushers and pullers, which induce different flow fields.

In such a situation, our simulations indicated polar orientational ordering for puller microswimmers, in contrast to pushers [1]. Thus, we analyzed the behavior of binary pusher–puller mixtures. Interestingly, we found that smaller amounts of pusher microswimmers can show a larger degree of orientational order than surrounding puller microswimmers in an ordered suspension of mainly pullers [1]. Increasing the amount of pushers makes the orientational order break down.

To further quantify these phenomena, we performed a linear stability analysis of a corresponding dynamical density functional theory for pusher and puller suspensions [2]. Indeed, we found homogeneous polar orientational order to arise from a linear instability of disordered suspensions of strong pullers, in contrast to pushers.

[1] G. Pessot et al., Mol. Phys. 116, 3401 (2018).

[2] C. Hoell et al., J. Chem. Phys. 149, 144902 (2018).