Activity induced asymmetric dispersion in confined channels with constriction

The behavior of particles passing narrow regions and/or constrictions has always been of special interest in traditional microfluidics. The situation becomes far more complex when the moving individuals are living bodies or artificial active particles. In a planar Poiseuille flow, the interplay of self-propulsion and the torque induced by the fluid flow (Jeffrey equation) leads to swinging and tumbling motion of micro-swimmers in the channel [1]. Using Brownian dynamics simulation, we have shown that the patterns of such motions in phase space are modified by imposing a funnel-like constriction in the channel, giving rise to an accumulation of the swimmers on one side of the constriction. Such symmetry breaking in density along the constricted channel, which is also reported in recent experiments [2], goes back to the appearance of attractors in phase space which traps the micro-swimmers in front of the constriction. Our results also indicate that the aspect ratio of elongated micro-swimmers, the ratio of fluid velocity to self-propulsion speed, and the channel confinement are relevant controlling parameters in this phenomenon.





[1] Zöttl, A., Stark, H., Physical Review Letters 108, 218104 (2012).



[2] E. Altshuler, G. Mino, C. Pérez-Penichet, L. del Río, A. Lindner, A. Rousseleta, and E. Clément, Soft Matter 9, 1864 (2013).