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Abstract:
Nematic liquid crystals are fluids whose anisotropic molecules have long range
orientational order, but no positional order. When the particles are driven by
some chemical or biological mechanism, the system is called active. The energy
supplied at the microscopic scale is transformed into organized motion at the large
scale. The coupling of the orientation field to the hydrodynamic and active forces
leads to rich, dynamical behaviors. We develop a framework for simulating such
active liquid crystals, based on the multiparticle collision dynamics algorithm
for hydrodynamics. The solver captures thermal fluctuations, is highly tunable,
and suited for complex boundary conditions. It is successfully validated against
analytical and numerical results of the isotropic-nematic phase transition, defect
annihilation, and activity. We use it to study the behavior of an active NLC
in cylindrical confinement, as well as in a deformed capillary with an elliptical
cross-section. Applying four different types of boundary conditions across a wide
range of activity magnitudes, we find a new non-equilibrium steady state. It is
characterized by two disclination lines orbiting the capillary center in ellipses of
varying aspect ratios. We find large asymmetries between extensile and contractile
active stresses for all steady states. The results are discussed in the context of
current research.
