Active boundary layers in confined active nematics

The role of boundary layers in conventional liquid crystals is commonly related to the mesogen anchoring on confining walls. In the classical view, anchoring enslaves the orientational field of the passive material under equilibrium conditions. In this work, we show that an active nematic can develop active boundary layers that topologically polarize the confining walls. We find that negatively-charged defects accumulate in the boundary layer, regardless of the wall curvature, and they influence the overall dynamics of the system to the point of fully controlling the behavior of the active nematic in situations of strong confinement. Further, we show that wall defects exhibit behaviors that are essentially different from those of their bulk counterparts, such as high motility or the ability to recombine with another defect of like-sign topological charge. These exotic behaviors result from a change of symmetry induced by the wall in the director field around the defect. Finally, we suggest that the collective dynamics of wall defects might be described in terms of a model equation for one-dimensional spatio-temporal chaos. The boundary of conventional liquid crystals is known to anchor the orientational field of the passive materials under equilibrium conditions. Here, the authors show an active nematic to develop active boundary layers that topologically polarize the confining walls regardless of the wall curvature.

Automated summary

This study reveals that active liquid crystals can develop active boundary layers that polarize the confining walls regardless of their curvature. The accumulation of negatively-charged defects in the boundary layer influences the dynamics of the system and can even fully control the behavior of the active liquid crystals.