Hedgehog defects in mixtures of a nematic liquid crystal and a non-nematogenic component

EZEQUIEL R. SOULÉ; ALEJANDRO D. REY

SOFT MATTER

ROYAL SOC CHEMISTRY

Año: 2012 vol. 8 p. 1395 - 1403

1744-683X

A theoretical study of the core structure and composition of a hedgehog defect in a mixture of a nematic liquid crystal and a second non-nematogenic component is presented. Fractionation of the components between the bulk and the defect core is rigourously considered by using solution thermodynamics. Two complementary approaches are used to analyze this problem: a multiscale model based in a Landau-DeGennes free energy functional that is solved numerically, and a macroscopic sharp interface phase-quilibrium model, which considers the defect core as an isotropic phase in equilibrium with a distorted nematic phase and that under certain limiting conditions yields equations that reveal the mechanisms that select defect core struture, geometry, and composition. It is found that the non-nematogenic component segregates preferentially to the defect core, and the defect radius  increases as the concentration of the second component and the temperature are increased. As previously  pedicted for pure liquid crystals, close to saturation conditions the radius increases significantly, and a small range of supersaturation or superheating is observed.