2010/09/20 by Irwin M. Zaid, Jörn Dunkel, Julia M. Yeomans · 62 citations
Biochemistry, Genetics and Molecular Biology · Materials Science · Physics and Astronomy · #Advanced Thermodynamics and Statistical Mechanics #Algae #Colloid #Diffusion #Field (mathematics) #Flow (mathematics) #Micro and Nano Robotics #Mixing (physics) #Pickering emulsions and particle stabilization #Suspension (topology) #TRACER #cond-mat.soft #cond-mat.stat-mech #physics.flu-dyn #q-bio.CB
paper · pdf · doi:10.1098/rsif.2010.0545
published in Journal of The Royal Society Interface 8(62), 1314-1331 (Royal Society)
arxiv created 2010/09/20 · openalex publication_date 2011/02/23 · arxiv updated 2013/02/04 · openalex created_date 2016/06/24 · openalex updated_date 2026/08/05
Swimming micro-organisms rely on effective mixing strategies to achieve efficient nutrient influx. Recent experiments, probing the mixing capability of unicellular biflagellates, revealed that passive tracer particles exhibit anomalous non-Gaussian diffusion when immersed in a dilute suspension of self-motile Chlamydomonas reinhardtii algae. Qualitatively, this observation can be explained by the fact that the algae induce a fluid flow that may occasionally accelerate the colloidal tracers to relatively large velocities. A satisfactory quantitative theory of enhanced mixing in dilute active suspensions, however, is lacking at present. In particular, it is unclear how non-Gaussian signatures in the tracers' position distribution are linked to the self-propulsion mechanism of a micro-organism. Here, we develop a systematic theoretical description of anomalous tracer diffusion in active suspensions, based on a simplified tracer-swimmer interaction model that captures the typical distance scaling of a microswimmer's flow field. We show that the experimentally observed non-Gaussian tails are generic and arise owing to a combination of truncated Lévy statistics for the velocity field and algebraically decaying time correlations in the fluid. Our analytical considerations are illustrated through extensive simulations, implemented on graphics processing units to achieve the large sample sizes required for analysing the tails of the tracer distributions.