Instability Driven Pattern Formation in Active Nematics

Active nematics represent a class of active systems, operating out of
thermodynamic equilibrium that consists of self-driven units with long-range
orientational ordering. Our numerical simulation was inspired by the experimental
observation of the development of deformation patterns of
branched, radially elongated elastic bands of the director field in
living liquid crystals (suspension of self-propelled swimming bacteria in
bio-compatible lyotropic liquid crystal).
As a model system, we chose a suspension of elongated rods which exerts extensile active
stresses and we employed the theory of active nematodynamics to study the
spatiotemporal dynamics of this system. The interplay of activity induced spontaneous
flow which drives the system away from the minimum of the free energy, and the
orientational ordering of the liquid crystal give rise to rich dynamical behavior
over length scales much larger than the size of each individual active entity.
Continuum simulations of the active nematic explain how activity fueled
instabilities result in appreciable spatial inhomogeneities of the nematic
ordering, giving rise to the formation of alternating bands of opposite curvature.
Our study examines regimes beyond experimental limits providing important
insights into the origin of the observed pattern.