Stirring by swimmers in confined microenvironments

Abstract

We consider the tracer diffusion $D_{rr}$ that arises from the run-and-tumble motion of low Reynolds number swimmers, such as bacteria. In unbounded dilute suspensions, where the dipole swimmers move in uncorrelated runs of length $\lambda$, an exact solution showed that $D_{rr}$ is independent of $\lambda$. Here we verify this result in numerical simulations for a particular model swimmer, the spherical squirmer. We also note that in confined microenvironments, such as microscopic droplets, microfluidic devices and bacterial microzones in marine ecosystems, the size of the system can be comparable to $\lambda$. We show that this effect alone reduces the value of $D_{rr}$ in comparison to its bulk value, and predict a scaling form for its relative decrease.

submitted to JSTAT

References in corpus (5)

• Fluid dynamics and noise in bacterial cell-cell and cell-surface scattering
• Direct measurement of the flow field around swimming microorganisms
• Diffusion and spatial correlations in suspensions of swimming particles
• Migration of chemotactic bacteria in soft agar: role of gel concentration
• Swimmer-tracer scattering at low Reynolds number

Cited by in corpus (4)

• Motility-induced phase separation and coarsening in active matter
• Magnetocapillary self-assemblies: locomotion and micromanipulation along a liquid interface
• Fluid transport and mixing by an unsteady microswimmer
• Focusing of Active Particles in a Converging Flow