Strong homeotropic anchoring requires radial orientation just outside a sphere, while the remote director is uniform. A plausible dipolar texture contains a compensating hyperbolic hedgehog defect on one side. The particle's radial boundary has charge under a consistent convention, balanced by an exterior point defect of charge so the far field is uniform. The original cross-section depicts this configuration.
An alternative has an equatorial Saturn-ring defect. Its local disclination winding is half-integer; that local winding is not itself the net three-dimensional compensating charge. Particle size, elastic constants, confinement and anchoring strength select between configurations. The elastic theory explicitly compares dipolar, Saturn-ring and surface-ring states.[ref]
Homeotropic anchoring means that the nematic director is locally normal to the particle surface, hence radial on a sphere. Far away, the uniform nematic liquid crystal has a fixed director , with and physically equivalent.
One plausible configuration is a quadrupolar Saturn-ring defect: the director is radial near the particle, bends into far away, and has a disclination loop just outside the particle's equator, in the plane perpendicular to . A meridional section cuts the loop at two points.
Figure 1.
Homeotropic surface anchoring matched to a uniform far-field director
. Original schematic Saturn-ring texture. Short rods represent a headless director; the two marked defect cores are intersections of a three-dimensional equatorial ring with the section. This is not a numerical free-energy minimizer. Source. Details.
The defect compensates the topological distortion introduced by the radial surface boundary condition. A dipolar configuration with a nearby hyperbolic point defect is another possible texture. Which is stable depends on particle size, anchoring strength, elastic constants and external confinement; the boundary conditions alone do not uniquely select one.[ref]