Dynamic phases and combing effects for elongated particles moving over quenched disorder

We consider a two-dimensional system of elongated particles driven over a landscape containing randomly placed pinning sites. For varied pinning site density, external drive magnitude, and particle elongation, we find a wide variety of dynamic phases, including random structures, stripe or combed phases with nematic order, and clogged states. The different regimes can be identified by examining nematic ordering, cluster size, number of pinned particles, and transverse diffusion. In some regimes we find that the pinning can enhance the particle alignment, producing a nonmonotonic signature in the nematic ordering with a maximum at a particular combination of pinning density and drive. The optimal nematic occurs when a sufficient number of particles can be pinned, generating a local shear and leading to what we call a combing effect. At high drives, the combing effect is reduced when the number of pinned particles decreases. For stronger pinning, the particles form a heterogeneous clustered or clogged state that depins into a fluctuating state with high diffusion. We consider a two-dimensional system of elongated particles driven over a landscape containing randomly placed pinning sites.

Automated summary

In this study, we investigate the dynamics of elongated particles in a two-dimensional system with randomly placed pinning sites. By varying the density of pinning sites, external drive magnitude, and particle elongation, we observe a wide range of dynamic phases including random structures, stripe or combed phases with nematic order, and clogged states. The effects of pinning sites on particle alignment result in nonmonotonic nematic ordering in certain regimes.