Dans un article récent, Lonberg et Meyer ont décrit une nouvelle forme de la transition de Freedericksz dans des polymères nématiques soumis à un champ magnétique et l'ont décrite en utilisant la théorie de l'élasticité de Frank et Oseen. Nous utilisons l'approche de Lonberg et Meyer pour étudier la possibilité d'existence de ce nouvel effet Freedericksz dans les cas d'orientation oblique du directeur ou du champ magnétique et pour différents rapports des constantes élastiques. Les résultats sont pertinents pour certains polymères nématiques et aussi pour des nématiques qui présentent également une phase smectique.

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The Oseen-Frank theory of curvature elasticity of nematic liquid crystals is used to investigate the occurrence of magnetic field-induced static periodic domains for weak anchoring of the nematic director at the sample boundaries. Planar and oblique director orientations are studied for different inclinations of a magnetic field applied in a plane normal to the initial director orientation. Comparison with results for rigid anchoring shows that weak anchoring can profoundly influence the formation of the periodic distortion. These results may be relevant to nematics of high elastic anisotropy, such as polymer nematics. The results are stated in some detail for symmetric anchoring ; consequences of asymmetric anchoring are briefly examined. It appears that it may not be possible to adapt results of this work to the case of nematics exhibiting a smectic phase via a simple symmetry transformation used earlier

This work reports theoretical studies on the occurence of a static periodic distortion (PD) in a nematic sample under the action of crossed electric (E) and magnetic (H) fields applied on a uniformly aligned initial director configuration (no ). Linear stability analysis with rigid anchoring hypothesis is employed. For homeotropic alignment of a nematic such as M1 which has negative dielectric anisotropy (ϵA<0) and positive diamagnetic anisotropy (χA>0), PD occurs when E and H are both in the sample plane. The direction of periodicity depends on the angle between E and H; PD is unfavorable when H is tilted sufficiently away from E. In a material (such as CCH-7) with ϵA>0 and χA<0, the direction of periodicity changes continuously in the H, E plane as a function of the strength and tilt of the stabilizing H relative to E. Possible effects of flexoelectricity, weak anchoring and director pretilt are discussed briefly

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