Alison E. Patteson: 0000-0002-4004-1734

Document Type



Winter 1-21-2016




National Science Foundation

Funding ID

NSF-DMR-1104705 and NSF-CBET-1437482


We would like to thank J. Crocker, S. Farhadi, N. Keim, D. Wong, E. Hunter, and E. Steager for fruitful discussions and B. Qin for help in the spectral analysis of data. This work was supported by NSF-DMR-1104705 and NSF-CBET-1437482.

Official Citation

Patteson, A. E., Gopinath, A., Purohit, P. K., & Arratia, P. E. (2016, January 21). Particle diffusion in active fluids is non-monotonic in size. Soft Matter. https://pubs.rsc.org/en/content/articlelanding/2016/sm/c5sm02800k#!divAbstract




We experimentally investigate the effect of particle size on the motion of passive polystyrene spheres in suspensions of Escherichia coli. Using particles covering a range of sizes from 0.6 to 39 microns, we probe particle dynamics at both short and long time scales. In all cases, the particles exhibit super-diffusive ballistic behavior at short times before eventually transitioning to diffusive behavior. Surprisingly, we find a regime in which larger particles can diffuse faster than smaller particles: the particle long-time effective diffusivity exhibits a peak in particle size, which is a deviation from classical thermal diffusion. We also find that the active contribution to particle diffusion is controlled by a dimensionless parameter, the Péclet number. A minimal model qualitatively explains the existence of the effective diffusivity peak and its dependence on bacterial concentration. Our results have broad implications on characterizing active fluids using concepts drawn from classical thermodynamics.

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Creative Commons Attribution 3.0 License
This work is licensed under a Creative Commons Attribution 3.0 License.

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