Clogging, Dynamics and Reentrant Fluid for Active Matter on Periodic Substrates
Theoretical Division, Los Alamos National Laboratory, Los Alamos, NM, USA
6 April 2022, 16:00 CEST
We explore the interactions between substrate length scales and correlation length scales of run-and-tumble active matter disks. For the case of a Casimir geometry of two plates placed a distance d apart, we show that an effective active-matter-mediated attraction arises due to a geometric shadowing effect . Next we shrink the plates down to columns and consider connections to jamming  and clogging effects  found in passive granular matter. The active particles are driven with an external force through columns placed in a square periodic array . When the drive is applied along a symmetry direction of the array, we find a clog-free uniform liquid state for low activity, while at higher activity, the density becomes increasingly heterogeneous and an active clogged state emerges in which the mobility is strongly reduced. For driving along non-symmetry or incommensurate directions, there are two different clogging behaviors consisting of a drive dependent clogged state in the low activity thermal limit and a drive independent clogged state at high activity. These regimes are separated by a uniform flowing liquid at intermediate activity. There is a critical activity level above which the thermal clogged state does not occur, as well as an optimal activity level that maximizes the disk mobility. Thermal clogged states are dependent on the driving direction while active clogged states are not .
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