Collective effects in doped nematic liquid crystals

We studied the collective elastic interaction in a system of many macropart icles embedded in a nematic liquid crystal. A theoretical approach to the i nteraction of macroparticles via deformation of the director field [1] is d eveloped. It is found that the director field distortion induced by many pa rticles leads to the screening of the elastic pair interaction potential. T his screening strongly depends on the shape of the embedded particles: it e xists for anisotropic particles and is absent for spherical ones. Our resul ts are valid for the homeotropic and the planar anchoring on the particle s urface and for different Frank constants. We apply our results to cylindric al particles in a nematic liquid crystal. In a system of magnetic cylindric al grains suspended in a nematic liquid crystal, the external magnetic fiel d perpendicular to the grain orientation results in inclining the grains to the director and induces an elastic Yukawa-law attraction between the grai ns. The appearance of this elastic attraction can explain the cellular text ure in magnetically doped liquid crystals in the presence of the magnetic f ield [2]. (C) 2001 MAIK "Nauka / Interperiodica".