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Tutorial Lectures

In document on Liquid Crystal Colloids (сторінка 75-83)

on Liquid Crystal Colloids

Emergent Phenomena and Functional Materials

Understanding of colloidal liquid crystals: Theory and experiment B. Lev

Institute of Physics, Nat. Acad. Sci. of Ukraine, 46, Nauky Prosp, Kyiv 02022, Ukraie

This article surveys new results on the interaction and the formation of structures in liquid crystal (LC) colloids and emulsions. We present the analytical results concerning the possible structures for suspensions of macroparticles in liquid crystals. We have shown that the formation of different structures can occur in liquid crystals for realistic values of the temperature and the concentration of macroparticles. If particles with dimensions being much larger than those of molecules of LC are immersed in LC, we can observe the peculiar properties in a new medium. Those can be solid insoluble particles or admixtures of another liquid introduced to LC. In the first and second cases, those are, respectively, LC colloids and emulsions. Because of a large enough surface, such particles prescribe boundary conditions for the orientation of LC molecules depending on the adhesion to that surface, which leads to a local deformation of the elastic field of the director. Two types of adhesion to the macrodoped surface are distinguished: the strong one and the weak anchoring. In the former case, the surface itself prescribes the director orientation and acts as a source of the director field change. In the latter case, each inclusion acts as a disturbance of the director orientation, because the boundary conditions at the surface do not correspond to the real distribution of the director.

First of all, we describe the influence of a separate macroinclusion on a deformation of the elastic field of the director and the scalar order parameter depending on a geometric configuration and dimensions, as well as the boundary conditions on the surface of a separate macroinclusion. It is shown, for instance, that the director distribution around a spherical inclusion under the normal boundary conditions on its surface has a topological defect existing as a hyperbolic hedgehog or a dislocation Saturn’s ring. Under tangent boundary conditions on the inclusion surface, the distribution of the director takes a spindle-like shape. If the area of a disturbance is large enough due to the overlapping of the director field deformation areas for two and more macroinclusions, there appears the effective interaction between them.

We have described the methods for determining the interaction energy through the elastic field of a director in the case of the strong or weak anchoring of LC molecules to the surface of a separate inclusion.

The effectiveness of such an interaction will be determined, first of all, by the geometric parameters of an inclusion, the adhesion force of LC molecules to the surface of such an inclusion, and the elastic properties of the medium. In the general case, the value and character of the interaction are determined by the value and character of a violation of the director distribution symmetry. We have shown how a violation of the director distribution symmetry at short-range distances defines the interaction at long-range distances.

Within the self consistency approach, we have determined the interaction between macroinclusions in nematic, smectic, and cholesteric LC. We have determined the interaction energy for macroinclusions in the isotropic phase of LC, and the effect of a change in the order parameter on the character and value of

T 1 Tutorial Lectures structures with different geometries can appear. We have studied the conditions for the appearance and mutual transformation of the possible periodic structures. We have explained the appearance of both a hexagonal structure in the system of glycerin drops with tangent boundary conditions and chain structures in the system of water drops with normal boundary conditions. We have described the possible structures that can be induced in view of the character of the obtained interaction and have studied the possibility for external fields to influence such structures.


Life and scientific achievements of Prof. Julius Planer

Myroslav Holovko,a Alexander Lutsykb and Rostyslav Bilyyb,c

aInstitute for Condensed Matter Physics, Ukraine

bDanylo Halytskyi Lviv National Medical University

cInstitute of Cell Biology, NAS of Ukraine

Prof. Julius Planer (Julius Planner von Plan) (13.VIII.1827 – 25.VII.1881) is an outstanding scientist who greatly contributed to both our understanding of malaria and of liquid crystals.

Julius Planer was born in Vienna where he obtained medical education and started his work in a famous Viennese pathologico-anatomical school. During 1855–1863 Prof. Planer headed Department of Anatomy at Lviv University. In 1863 he moved to the city of Graz, where he headed Chair of Department of Anatomy, Medical Faculty, University of Graz during 1863 – 1881.

Scientific interest of Prof. Planner mainly included descriptive and topographical anatomy. He founded Museum of pathological-anatomy at Lviv University as well as enriched physiological and anatomical collections of the University. While working in Lviv University he made his probably most important scientific discovery – the discovery of cholesteric liquid crystals. Another important Prof. Planer’s scientific discovery included study of the occurrence of pigment granules in the blood, particularly the indication of their relation to the course of intermittent fever.

Marian Smoluchowski’s work at the University of Lviv (1899 – 1913) Andrij Rovenchak

Department for Theoretical Physics, Ivan Franko National University of Lviv, Ukraine

The presentation is an overview of Marian Smoluchowski’s activities at the University of Lviv, where he has worked for about 14 years as a professor of theoretical physics. This period was the most fruitful time for his scientific work, leading to novel studies in the field of theory of fluctuations, Brownian motion, kinetic theory of colloids, etc. During 1899–1913, Marian Smoluchowski authored about eighty publications, including numerous papers and several textbooks; the list can be accessed at http://www.ktf.franko.

lviv.ua/cgi-bin/select.cgi?Smoluchowski. A short analysis of these works is planned.

on Liquid Crystal Colloids

Emergent Phenomena and Functional Materials

In document on Liquid Crystal Colloids (сторінка 75-83)