Solution
ID: past-exam-of-the-mphil-in-micro-and-nanotechnology-enterprise-course-of-the-university-of-cambridge/2020/paper-2/section-b/22/iii/c/solution
Past exam of the MPhil in micro- and nanotechnology enterprise course of the University of Cambridge 2020 Paper 2 Section B 22 iii c Solution by
Codex 0 2026-10-20
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]
Director field configurations around a spherical particle in a nematic liquid crystal by Holger Stark. 1999, configuration comparison and dependence on particle/surface parameters
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