Coherent motion of dense active matter

Amin Doostmohammadi,Julia M Yeomans

doi:10.1140/epjst/e2019-700109-x

Amin Doostmohammadi, Julia M Yeomans

Open Access

https://doi.org/10.1140/epjst/e2019-700109-x

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Abstract

We discuss experiments, simulations and theories showing how active nematics behave in circular and linear confinement, and in the presence of friction. In each case active turbulence can be suppressed resulting in steady or periodic flows. These have the potential to act as power sources, transforming chemical energy to mechanical work, and we review first steps in this direction.

Highlights

Active matter takes energy from its surroundings on a single particle level and uses it to do work, often in the form of movement
For example Galajdi et al [55] placed bacteria in a chamber containing a line of v-shaped funnels and found that the bacteria preferentially collected on one side of the obstacles, away from the point of the ‘v’
Similar behaviour has been seen for cells in asymmetric geometries: as the direction and speed of the motion depends on the details of the cell motility this suggests a route for sorting different kinds of cells [56,57]

Summary

Introduction

Active matter takes energy from its surroundings on a single particle level and uses it to do work, often in the form of movement. Defects appear in dense systems [11,12] but the reasons for this are not fully understood Both polar and nematic active particles that are self-propelled with no external forces produce stresslet far flow fields with nematic symmetry. The distortions in the director field give rise to flow jets and a velocity field that is characterised by high vorticity (Fig. 1) This dynamical state is termed active or mesoscale turbulence, and is described in more detail in the Geilo notes from the 2015 school ([14] and references therein). It is interesting to consider ways to ‘tame’ active turbulence, channelling the energy input into coherent flows In these notes we summarise recent research showing how this can be done by screening hydrodynamic effects through confinement, or by friction. We discuss possible ways of applying the understanding gained from active flows in confinement to designing active microfluidics and active micromachines in the light of recent experimental and computational advances in these directions

Active flow in confinement

Circular confinement

Theories and simulations

Experiments

Friction

Discussion