Proceedings PaperRefractive profiles of chiral-nematic myelin filaments
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Two main types of the striped domains in thin layers of chiral nematics can be distinguished: 1 . chiralBloch4ype domain walls placed between two neighbouring homeotropic regions which are indUced in chiral nematic layers by surface interactions ofthe chiral nematic liquid and glass plates; 2. cylindrical myelin filaments freely suspended within homeotropic nematic matrix induced in a chirahnematic thin layer by surface interaction or by an action of external electric (or magnetic) fields. The myelin filaments when oriented perpendicularly to the glass support are visible as the bubble domains and can be hexagonally packed within some regions ofthe layer. The Bloch-type walls have been investigated by T. Akahane and co-workers  with the use ofthe differential interference method. The cylindrical chiral myelins are observed at the front of diffusion of the chiral mixture into a homeotropic nematic layer or near the saturation region in the electrically induced phase transition N N. The structure of the myelin filaments has been proposed as a set of coaxial cylinders having the chiral-nematic molecular ordering with radially oriented screw axis . Here, the cylindrical structure of the chiral myelins is confirmed by means of the Pluta fringe-field birefracting niicrointerferometiy. By directly measuring the distribution of the main refractive indices n1 and nas well as their difference n over perpendicular cross-sections of myelin filaments, this technique reveals microscopic features of the molecular arrangement within filaments. Computer models of the molecular structure based on the microinterferometric data are presented.