Spatial Variation of Transport Properties of Active Brownian Particles

Self-propelling microswimmers such as motile bacteria and Janus particles can be modeled as Active Brownian Partices (ABPs) and characterized by their transport properties: swim speed, translational diffusivity, and rotational diffusivity. We have developed a general theory to decribe suspensions of ABPs with spatialy varying transport properties. We find that the number density distribution of ABPs is primarily governed by the swim speed and is always lower in the region with the faster swim speed as first shown by Tailleur & Cates (PRL 2008). We also show that the translational diffusivities of ABPs smooth out the effect of the variation of swim speed. The theory implies that spontaneous reverse-osmosis is achievable owing to the spatial variation of the swim speed of active matter.