Role of obstacle softness in the diffusive behavior of active particles

Abstract

We numerically investigate the diffusive behavior of active Brownian particles in a two-dimensional confined channel filled with soft obstacles, whose softness is controlled by a parameter K. Here, active particles are subjected to an external bias F. Particle diffusion is influenced by entropic barriers that arise due to variations in the shape of the chosen channel geometry. We observed that the interplay between obstacle softness, entropic barriers, and external bias leads to striking transport characteristics of the active particles. For instance, with increasing F, the non-linear mobility exhibits a non-monotonic behavior, and effective diffusion is greatly enhanced, showing multiple peaks in the presence of soft obstacles. Furthermore, as a function of K and F, particles exhibit various diffusive behaviors, e.g., normal diffusion—where the role of obstacles is insignificant, and subdiffusion or superdiffusion—where the particles are partially trapped by the obstacles, and the particles are ultimately caged by the obstacles. These findings help understand the physical situations wherein active agents diffuse in crowded environments.