Active Colloidal Suspensions Exhibit Polar Order under Gravity
Abstract
Recently, the steady sedimentation profile of a dilute suspension of chemically powered colloids was studied experimentally [J. Palacci , Phys. Rev. Lett. 105, 088304 (2010)PRLTAO0031-900710.1103/PhysRevLett.105.088304]. It was found that the sedimentation length increases quadratically with the swimming speed of the active Brownian particles. Here we investigate theoretically the sedimentation of self-propelled particles undergoing translational and rotational diffusion. We find that the measured increase of the sedimentation length is coupled to a partial alignment of the suspension with the mean swimming direction oriented against the gravitational field. We suggest realistic parameter values to observe this polar order. Furthermore, we find that the dynamics of the active suspension can be derived from a generalized free energy functional.
- Publication:
-
Physical Review Letters
- Pub Date:
- July 2011
- DOI:
- 10.1103/PhysRevLett.107.058301
- arXiv:
- arXiv:1105.5554
- Bibcode:
- 2011PhRvL.107e8301E
- Keywords:
-
- 82.70.Dd;
- 47.57.ef;
- 47.63.Gd;
- Colloids;
- Sedimentation and migration;
- Swimming microorganisms;
- Condensed Matter - Soft Condensed Matter
- E-Print:
- This paper has been withdrawn