LABORATORY
LIQUID CRYSTALS

HEAD: Assoc.Prof. Marin Mitov, Ph.D.
tel: 7144-372; e-mail: mitov@issp.bas.bg

TOTAL STAFF: 8
RESEARCH SCIENTISTS: 7

Cor.mem. Prof. A.Derzhanski, Ph.D., Dr.Sc.
Assoc.Prof. H.Hinov, Ph.D.
Assoc.Prof. A.Zheliaskova, Ph.D.
Assoc.Prof. I.Bivas, Ph.D.
Assist.Prof. Radoslav Marinov, Ph.D.
Assist. Prof. V.Vitkova, Ph.D
J.Genova, Ph.D. student.

RESEARCH ACTIVITIES:

    Six projects have been developed in Laboratory of Liquid Crystals during 2003 year on different contracts: two with BAS, one with NSF, one with RAS, two with CNRS, one of which in the framework of French-Bulgarian Laboratory "Vesicles and Membranes".

    The model proposed in 2002 for explanation of the flexo-dielectric walls in nematics has been improved and supported by theoretical considerations. Three-dimensional flexoelectric domains of Vistin'-Bobylev-Pikin in the liquid crystal p-n-butyl-p-methoxyazoxy-benzene (BMAOB) with asymmetrical strong-weak anchoring have been experimentally studied. The threshold voltage and the period have been obtained under the joint action of d.c. and a.c. electric fields. The theory which should explain the obtained experimental results is under way. Thirty years later a comment of the "gradient flexoelectric effect" in nematics has been made and some topic questions have been raised. The gradient flexoelectric effects have been discussed on the basis of the electro-chemical behavior of the liquid crystal.

    The boundaries are outlined of the two-phase regions around the liquid crystalline phase in the binary system Triton X-114 - water. The phase behavior is studied as a function of the concentration of the detergent in the system and of the temperature. The phase diagram contains an eutectic point, appearing as the peak with respect to temperature of the existing there liquid crystal domain.

    The changes in the colour characteristics of Alternating Current Hybrid electroluminescent structures with yellow emission, as a function of the type of the protective layer, are investigated. Conclusions for the possible applications of some of the investigated HEL structures in various systems for representation of colour sign information are given.

    The influence of doped antimony and fluorine ions on the properties of SnO₂ thin films were examined. The absorption curves of SnO₂:F, Sb films were taken down. Possibilities for application of these doped SnO₂ films as transparent electrodes in electroluminescent and liquid crystal display structures were discussed.

    The upper and lower part of an emulsion, stabilised by 12 wt. % EY and stored 18 days, were subjected to shear and the drop size distributions before and after this treatment were measured by NMR and compared. There is no significant change in drop size distribution between the upper and lower parts of the emulsion before shearing. Formation of drops with larger diameters was observed for the upper part of the cream after shearing. On the contrary, no change in drop size distribution was observed for the lower part of the cream after shearing. This result clearly show that the destabilisation started in the upper part of the emulsion cream, which is in contact with air.

    The water permeability of lipid membranes in presence of different concentrations of natural peptide alamethicin at different pressure differences have been investigated. A fifteen-fold increase of water permeability is observed at 7 mM alamethicin.

    A new experimental technics for studying the giant vesicles morphology has been used to investigate the influence of alamethicin on vesicles shapes. Strong and reversible changes has been observed at concentration of 7 mM alamethicin.

    The bending elastic constant of DPhPC was measured using the stroboscopic video microscopy. The value obtained, k_c=(1.23±0.06) x10^-19J, is in good agreement with the value measured by others using standard illumination and "correction factor" k_c=(1.17±0.1)x10^-19J.

    Most of the existing theories of the electric fields and forces around a channel in a planar membrane oversimplify the electric field distribution by placing the electrode directly at the entry of the channel. However, in any relevant experimental setup the electrodes are placed far away in the electrolyte solution. It was demonstrated that long range deformation of the electric field distribution appears around the membrane, spanning on distances of the order of the distance between the membrane and the electrode. The forces, acting due to this distribution, are important for channels with radii of the order of the thickness of the layer of structured water at the interface oil-water.

1. H. P. Hinov, I. Bivas, M. D. Mitov, K. Shoumarov, Liq. Cryst., 30, 945, 2003.
2. H. P. Hinov, I. Bivas, M. D. Mitov, K. Shoumarov, Y. Marinov, Liq. Cryst. 30, 1293, 2003.
3. S. Naydenova, A. Zheliaskova, R. Ugrinov, Y. Marinov, A.G.Petrov, J. Mater. Sci.: Mater. El., 14, 815-816, 2003.
4. V. Vitkova, J. Genova and P. Meleard, J. Mater. Sci.: Mater. El. 14, 819-820, 2003.
5. I. Bivas and P. Meleard, Phys. Rev. E, 67, 012901, 2003.
6. I. Bivas and C. Danelon, Phys. Rev. E. (in press).
7. S. Panayotova, I. Bivas, Bulg. J. Phys. (in press).
8. L. Yourukova, K. Kolentsov, A. Zheliaskova, Bulg. J. Phys. (in press).
9. K. Kolentsov, L. Yourukova, A. Zheliaskova, A. Rachkova, Bulg. J. Phys. (in press).
10. S. Tcholakova, R. Marinov, N. Denkov , I. Ivanov, Bulg. J. Phys. (in press).
11. J. Genova, V. Vitkova, L. Aladgem, P. Meleard, M. D. Mitov, Bulg. J. Phys. (in press).
12. H. Hinov, Bulg. J. Phys. (in press).
13. K. Kolentsov, L. Yourukova, T. Kehlibarov, A. Zheliaskova, Tekstil i obleklo, 8, 11, 2003.

1. "French-Bulgarian laboratory - Vesicles and Membranes" - CNRS, France.
2. "Influence of surface electric charges on mechanical properties of lipid membranes and monolayers" - Institute of Electrochemistry, Moscow, Russia.
3. "Mechanical, electromechanical, and electromagnetic properties of lipid monolayers and bilayers" - Institute of Pharmacology and Structural Biology, CNRS, Toulouse, France

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