Eur. Phys. J. E 9, 341-347 (2002)
DOI: 10.1140/epje/i2002-10087-y

Colloidal interactions in two-dimensional nematics

M. Tasinkevych¹, N.M. Silvestre¹, P. Patrício^{1, 2} and M.M. Telo da Gama<sup>1

1</sup>  Departamento de Física da Faculdade de Ciências and Centro de Física Teórica e Computacional, Universidade de Lisboa, Avenida Professor Gama Pinto 2, P-1649-003 Lisboa Codex, Portugal
²  Instituto Superior de Engenharia de Lisboa, Rua Conselheiro Emídio Navarro 1, P-1949-014 Lisboa, Portugal

miko@cii.fc.ul.pt

(Received 1 October 2002 and Received in final form 12 November 2002 / Published online: 21 January 2003)

Abstract
The interaction between two disks immersed in a 2D nematic is investigated i) analytically using the tensor order parameter formalism for the nematic configuration around isolated disks and ii) numerically using finite-element methods with adaptive meshing to minimize the corresponding Landau- de Gennes free energy. For strong homeotropic anchoring, each disk generates a pair of defects with one-half topological charge responsible for the 2D quadrupolar interaction between the disks at large distances. At short distance, the position of the defects may change, leading to unexpected complex interactions with the quadrupolar repulsive interactions becoming attractive. This short-range attraction in all directions is still anisotropic. As the distance between the disks decreases, their preferred relative orientation with respect to the far-field nematic director changes from oblique to perpendicular.

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

© EDP Sciences, Società Italiana di Fisica, Springer-Verlag 2002