Domain walls in two-dimensional nematics confined in a small circular cavity

D. de las Heras, and E. Velasco
Soft Matter, 10, 1758, (2014)     DOI: 10.1039/C3SM52650J
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Using Monte Carlo simulation, we study a fluid of two-dimensional hard rods inside a small circular cavity bounded by a hard wall, from the dilute regime to the high-density, layering regime. Both planar and homeotropic anchoring of the nematic director can be induced at the walls through a free-energy penalty. The circular geometry creates frustration in the nematic phase and a polar-symmetry configuration with a distorted director field plus two +1/2 disclinations is created. At higher densities, a quasi-uniform structure is observed with a (minimal) director distortion which is relaxed via the formation of orientational domain walls. This novel structure is not predicted by elasticity theory and is similar to the step-like structures observed in three-dimensional hybrid slit pores. We speculate that the formation of domain walls is a general mechanism to relax elastic stresses under the conditions of strong surface anchoring and severe spatial confinement.

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Uniaxial order parameter
The figure shows the uniaxial order parameter profile (black: no orientational order, yellow: perfect orientational order) in three different states. (left) Isotropic, here there is no orientational order (low density state). (middle) Nematic with two point defects (stable at intermediate densities). (right) Nematic with domain walls (stable at high densities).

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