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Director field configurations around a spherical particle in a nematic liquid crystal

  • H. Stark
Article

Abstract:

We study the director field around a spherical particle immersed in a uniformly aligned nematic liquid crystal and assume that the molecules prefer a homeotropic orientation at the surface of the particle. Three structures are possible: a dipole, a Saturn-ring, and a surface-ring configuration, which we investigate by numerically minimizing the Frank free energy supplemented by a magnetic-field and a surface term. In the dipole configuration, which is the absolutely stable structure for micron-size particles and sufficiently strong surface anchoring, a twist transition is found and analyzed. We show that a transition from the dipole to the Saturn ring configuration is induced by either decreasing the particle size or by applying a magnetic field. The effect of metastability and the occurrence of hysteresis in connection with a magnetic field are discussed. The surface-ring configuration appears when the surface-anchoring strength W is reduced. It is also favored by a large saddle-splay constant K24. A comparison with recent experiments [#!itapdb:Poulin1997!#,#!itapdb:Poulin1998!#] gives a lower bound for W, i.e., W >0.06erg/cm2for the interface of water and pentylcyanobiphenyl (5CB) in the presence of the surfactant sodium dodecyl sulfate.

PACS. 77.84.Nh Liquids, emulsions, and suspensions; liquid crystals - 61.30.Cz Theory and models of liquid crystal structure - 61.30.Jf Defects in liquid crystals 

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Copyright information

© EDP Sciences, Springer-Verlag 1999

Authors and Affiliations

  • H. Stark
    • 1
  1. 1.Institut für Theoretische und Angewandte PhysikUniversität Stuttgart, Pfaffenwaldring 57StuttgartGermany

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