Anomalous Brownian motion of colloidal particles in a nematic environment Taras Turiv,a Alexander Brodina,b and Vasili Nazarenkoa
aInstitute of Physics NAS Ukraine, Kyiv, Ukraine
bNational Technical University of Ukraine “Kyiv Polytechnic Institute”, Kyiv, Ukraine
Using video microscopy and single particle tracking, we investigate thermal motion of colloidal particles in a nematic liquid crystal. At long times, compared to the characteristic time τ ≈ 50 ms of the nematic director dynamics in the configurations that we use, we observe typical, albeit anisotropic Brownian motion with the mean square displacement (MSD) linear in time and inversely proportional to the effective viscosity of the nematic medium. At shorter times, however, the dynamics is markedly nonlinear and exhibits subdiffusive (slower than∝ t) evolution of MSD. These results are discussed in the context of coupling of the colloidal particle dynamics to the dynamics of the nematic host. We devise a theoretical model of the phenomenon that adequately describes the experimental results.
Theory of elastic interaction between colloidal particles in the nematic cell in the presence of an electric or magnetic field
S. B. Chernyshuk,a O. Tovkachb and B. I. Levb
aInstitute of Physics, NAS Ukraine, Prospekt Nauki 46, Kyiv 03650, Ukraine
bBogolyubov Institute of Theoretical Physics, NAS Ukraine, Metrologichna 14-b, Kyiv 03680, Ukraine
The Green function method developed in  is used to describe elastic interactions between axially sym- metric colloidal particles in the nematic cell in the presence of an external electric or magnetic field. General formulas for dipole-dipole, dipole-quadrupole and quadrupole-quadrupole interactions in the homeotropic and planar nematic cells with parallel and perpendicular field orientations are obtained. A set of new results has been predicted: 1) Deconfinement effect for dipole particles in the homeotropic nematic cell with negative dielectric anisotropy ∆ < 0 and perpendicular to the cell electric field when electric field is approaching it’s Frederiks threshold value E ⇒ Ec. This means cancellation of the confinement effect found in  for dipole particles near the Frederiks transition while it remains for quadrupole particles. 2) New effect ofattraction and stabilization of the particles in the homeotropic nematic cell along the electric field parallel to the cell planes. The minimun distance between two particles depends on the strength of the field and can be ordinary for ∆ <0. 3) Attraction and repulsion zones for all elastic interactions are changed dramatically under the action of the external field.
 S. B. Chernyshuk and B. I. Lev, Phys. Rev. E81, 041707 (2010)  M.Vilfan et al. Phys.Rev.Lett. 101, 237801, (2008)
The role of dipole-dipole correlations on biaxial ordering in the bent-core liquid crystals Grzegorz Pająka,b and Mikhail Osipovb
aMarian Smoluchowski Institute of Physics, Department of Statistical Physics and Mark Kac Center for Complex Systems Research, Jagiellonian University, Reymonta 4, Kraków, Poland
bDepartment of Mathematics and Statistics, University of Strathclyde, Livingstone Tower, Richmond Street, Glasgow, Scotland, UK
Bent-core mesogenic molecules are known to possess a pronounced polar shape and a large transverse permanent dipole. These polar molecular properties lead to a strong flexoelectric effect in the nematic liquid crystals . Moreover, electrostatic and primarily dipole-dipole interactions between bent-core molecules make a significant contribution to the stabilization of the biaxial nematic ordering as shown by atomistic computer simulations .
The existing molecular theory of bent-core nematics is developed predominantly in the mean-field approximation. One notes, however, that polar intermolecular interactions cannot be taken into account in this approximation because the nematic phase is nonpolar and thus all one-particle averages of polar quantities must vanish. Thus the dipolar interactions in the nonpolar phase manifest themselves via dipole- dipole correlations which should be taken into account using a more advanced approach. In contrast, the theory of flexoelectricity can be developed in the mean-field approximation because it is determined by a polar correction to the orientational distribution function proportional to the gradients of the director.
The effect of short-range intermolecular correlations has been studied using the two-particle cluster approximation and the model of a bent-core molecule composed of two uniaxial arms and the central transverse dipole. The full intermolecular potential for such particles is expanded and expressed in terms of couplings between first-, second- and third-rank molecular tensors. Depending on the values of opening angle and electric dipole, we have studied in detail the influence of dipole-dipole correlations on the stability of the biaxial phase and on temperature variation of the order parameters in this model. Moreover, the flexoelectric coefficients have been calculated numerically as functions of temperature in the mean-field approximation taking into consideration all dipolar contributions. We also present the results for the temperature variation of short-range polar order parameters in the nonpolar nematic phases calculated for various values of coupling coefficients in the model.
Acknowledgments: This work is supported by EPSRC grant (EP/H046941/1) which is a part of the International Materials World Project.
 J. Harden, B. Mbanga, N. Éber, K. Fodor-Csorba, S. Sprunt, J. T. Gleeson, A. Jákli, PRL 97, 157802
Possible mechanism of formation of anisotropic textures in DNA films S.M. Perepelytsya,a G.M. Glibitskiyb and S.N. Volkova
aBogolyubov Institute for Theoretical Physics, NAS of Ukraine, 14-b Metrolohichna St., Kiev, 03680
bUsikov Institute of Radiophysics and Electronics, NAS of Ukraine, 12 Ak. Proskura St., Kharkov, 61085
Under the presence of special excess salts the DNA macromolecules may form the textures in dry films.
The mechanism of counterion influence on texture formation in DNA films is not determined yet. In the present work the formation of anisotropic textures in dry films of DNA with chlorides of alkaline metals is studied. The films are prepared by evaporating water solution of DNA from calf thymus with excess salt 10 mM. The obtained DNA films with NaCl, KCl, and RbCl salts are characterized by dendritic textures, while in the case of LiCl and CsCl do not. To determine the character of interaction between DNA macromolecules the interaction energy between two parallel unlimited double helixes is estimated for different degree of phosphate neutralization. The results show that the macromolecules attract when the negatively charged phosphate groups of DNA backbone are completely neutralized. Otherwise the macromolecules repel. In the case of NaCl, KCl, and RbCl the analysis show that the phosphate groups of the double helix are neutral before the DNA coil is squeezed between surface of the film and substrate.
This a process leads to the formation of anisotropic textures in the film. In the case of LiCl and CsCl excess salts the total neutralization of DNA phosphate groups occurs when the coil size is about the same as the thickness of the film. Under such conditions the DNA macromolecules precipitate on the substrate that interrupts the formation of anisotropic textures.
Soft matter made of hard spheres. Synthesis of liquid crystalline hybrid nanomaterials.
Michał Wójcik, Wiktor Lewandowski, Milena Kołpaczyńska, Monika Góra, Józef Mieczkowski, Ewa Górecka
Faculty of Chemistry, Warsaw University, Pasterua 1, 02-093 Warsaw, Poland
Liquid crystals are now playing a very significant role in nanoscience and nanotechnology. Liquid-crystal nanoscience primarily deals with the synergetic relationship between liquid crystals and nanomaterials.
Therefore various nanomaterials have been dispersed and studied in LC medium to enhance the physical properties of LC, but the most important, from technological point of view is how to obtain stable organic- inorganic LC materials having new photonic properties.
In the presentation there will be shown how to synthesize novel liquid crystalline soft materials made of modified nanoparticles using various mesogenic molecules. Such a hybrid materials consist of metallic cores pasivated with covalently attached mesogenic organic molecules. During our investigations we used different models of organic molecules such like simple rod-like moleculs, boalamphiphilic compounds or more recently LC-polymers. Most of those materials possess a well defined long-range three dimensional order made of metallic objects [1, 2, 3].
O Si H
O Si H
O Si H
O Si H
NH C H3
Figure 2: Model of hybrid liquid crystal nanomaterial and structures of various mesogenic ligands used for surface modification.
Memory type colloids based on liquid crystals and carbon nanotubes
O. Yaroshchuk,a S. Tomylko,a O. Kovalchuk, N. Lebovkab and R. Yamaguchic
aInstitute of Physics, NASU, prospekt Nauki 46, 03028 Kyiv, Ukraine
bInstitute of Biocolloidal Chemistry NASU, prosp. Vernadskoho 42, Kyiv, Ukraine
cEEE Dept., Akita University, 1-1 Tegatagakuen-cho, Akita, 010-8502, Japan.
In this report we describe liquid crystal (LC) colloids of carbon nanotubes (CNT) with a function of electro-optic memory. This memory effect is attained in the homeotropically aligned layers of the colloids based on nematic LCs with∆ε <0 and concentration of CNTs close and above its critical value charac- terizing percolation transition in these systems [1, 2]. The essence of the memory effect is that the cycle of electric field irreversibly transfers the colloid layer placed between two crossed polarizers from dark to bright state. The model is proposed and substantiated according to which the planar state of LC achieved in the electric field is stabilized by the network of nanotubes formed upon the disintegration of CNT aggregates under the action of electrohydrodynamic flows. The efficiency of the electro-optic memory was further doubled by doping LC with small amount of chiral dopant (ChD) due to enhancement of stabilizing effect of CNT network [2, 3]. New possibilities in controlling the memory efficiency open when using ChDs capable to photoisomerization. This allows one to control with an actinic light a twisting tension in the colloids and in this way maximize electro-optic memory or switch the cells from the memory mode to the reversible mode typical for the vertically aligned LC layers. The obtained results give real application prospects to the memory type LC-CNTs colloids, especially in displays as well as information storage and processing systems based on the LC materials.
 L. Dolgov, O. Yaroshchuk, & N. Lebovka, Mol. Cryst. Liq. Cryst., 496, 212 (2008).
 L. Dolgov, S. Tomylko, O. Koval’chuk, N. Lebovka and O. Yaroshchuk, Liquid crystal dispersions of car- bon nanotubes: dielectric, electro-optical and structural peculiarities. In book “Carbon nanotubes”, Jose Mauricio Marulanda (Ed.), INTECH (2010). http://sciyo.com/books/show/title/carbon-nanotubes.
 L. Dolgov, S. Tomylko, T. Semikina, O. Koval’chuk and O. Yaroshchuk, Diamond and Related Mate- rials, 19, 567-572 (2010).
on Liquid Crystal Colloids