Magnetic Orientation of Nematic Lyomesophases

Abstract

Quantitative estimates are made for the diamagnetic mean susceptibility and anisotropy of the micellar interior and of the solvent medium of typical nematic lyomesophases. An analysis of the possible orienting mechanisms shows that both the molecular diamagnetic anisotropy of the hydrocarbon chains, which tends to align the chains perpendicular to the field, and the diamagnetic form anisotropy, which tends to align the major axis of the ellipsoids in the direction of the field, could in principle be responsible for the observed orientation if the micellar units are elastically coupled together, since the magnetic energy of a single micelle is smaller than thermal fluctuations. However, the degree of correlation among chains ensures that shape anisotropy of the micelles is negligible in front of molecular diamagnetic anisotropy, which must be responsible for the orientation of these lyomesophases.