Thermotropic Liquid Crystals
The leading scientists were Acad. A. Derzhanski, PhD, DSc., Assoc. Prof. H. Hinov, PhD, Acad. A. G. Petrov, PhD, DSc (till 1990)
 | Flexoeffect in nematics; |
| Methods for the study of liquid crystals by use of the total internal reflection (experiment and theory), a simultaneous application of DC voltage and AC voltage with a high frequency above the cut-off frequency of the dielectric relaxation of the space charges (experiment and theory); |
| Influence of the surface anchoring on nematics, large-pitch cholesterics and smectics on their electrooptic and elastic behavior; |
| Textures and electrooptic effects in liquid-crystaline polymers; |
| Influence of the second order elasticity on the electric and elastic response of nematics; |
| Observation of new electrooptic effects in nematics, large-pitch cholesterics and smectics which can be applied in the practice; |
| Experimental observations of the formation of small sessile water droplets attached to the glass plates of the liquid crystal cells containing nematic and a small quantity (several weight %) of water. A study of the influence of surface active materials on this phenomenon. |
Nuclear Magnetic Resonance Activity
The leading scientists were Acad. Alexander Derzhanski, PhD, DSc, Assoc. Prof. Antonia Zheliaskova, PhD, Assist. Prof. Radoslav Marinov, PhD
| Investigation of lipid – water systems by NMR; |
| Investigation of lipid – surfactant - water systems by NMR; |
| Nuclear magnetic resonance apparatus for measuring the spin-lattice relaxation time T1; |
| Application of low resolution NMR for determination of drop-size distribution of oil-in-water emulsions. |
The scientific research on liquid crystal physics in the Institute of Solid State Physics (ISSP), Bulgarian Academy of Sciences (BAS), has begun in 1968 when the founder of the Laboratory of Liquid Crystals - Alexander Derzhanski, now Academician, has finished his PhD thesis entitled “A new method for detection of NMR absorbtion”. He was looking for a new object for his further research, an object for which the NMR is a useful and efficient research method. Due to his persistent interest at computing and measuring electronics he looked for an object that can play an essential role in this domain too. He had already searched the scientific literature and was familiar with the state of research in the field of organic semiconductors, ferroelectrics and polymers when he found an announcement of RCA stating that they (at RCA) work on a new type of electrooptical digital indicator exploiting the properties of liquid crystals and that is compatible with integrated circuits due to its inherent low voltage and low power requirements. Another point was that during the PhD studies of A. Derzhanski in the NMR Laboratory of Professor A. Loesche in Leipzig University he was already introduced to his NMR investigations on liquid crystals.
The Laboratory of Liquid Crystals in the early seventies /From left to right: Acad. Alexander G. Petrov, Acad. Alexander Derzhanski, Assoc. Prof. Hristo Hinov, D. Sc. Ph.D., Assoc. Prof. Marin D. Mitov, Ph.D./ from: Vera Datcheva, “Crystals in a glass”, in Spectar’84, Sofia (1984)
The founder of the Laboratory of Liquid Crystals,
tells about the creation and the developement of the Laboratory during its early years:
The scientific policy of the Bulgarian Academy of Sciences at this time demanded industrial applications of the new scientific results. Initiated by the Institute of Solid State Physics, BAS, the Research Center of the Industrial Union for Computing “ISOT” included in his research program preliminary studies of liquid crystals with respect to eventual further application and production of liquid crystal digital displays in Bulgaria. In parallel with the methodological studies on the application of pulsed NMR in the physics of liquid crystals the scientists of the Laboratory of Liquid Crystals performed experimental investigations and thorough search in the literature on the stability and lifetime of liquid crystal displays under the influence of different chemicals at different regimes of electrical excitation. Initiated as purely preliminary and technologically oriented these studies naturally evolved into purely fundamental. In wide front: the mechanisms of current conductivity in liquid crystals; the space distribution of charges and ions, electrodes phenomena, polarization and orientation effects; the elastic properties of liquid crystals of first and second order, in the bulk and at the interface; the initial orientation of LC; the dielectric properties and orienting influence of electric fields was studied. During this investigations the gradient flexoelectic effect was discovered, a phenomenon that was broadly investigated and confirmed later on in the Laboratory as well as by renown groups in Harvard, Bordeaux and Orsay Universities. The results of Sofia Liquid Crystal Group attracted the attention of the scientific community and the members of the Laboratory became welcome partners, coorganizers, organizers and invited lecturers of scientific conferences. The Liquid Crystal Laboratory extended the field of interests with respective increase of the staff. The scientists of the Laboratory obtained their PhD degrees and habilitations working on their specific scientific problems. Each of them developed as a leader in his scientific domain. Alexander Petrov defended his PhD and DSc theses, obtained a title of Professor, was active in research of flexoeffect in thermotropics and subsequently in lyotropic systems (liquid crystals and membranes). On this basis he developed investigations on living membranes and in 1990 created a new laboratory - the Laboratory of Biomolecular Layers. Hristo Hinov has been active for many years in the field of elasticity of second order in thermotropic liquid crystals, ferroelectricity and flexoelectricity. Antonia Zheliaskova is active mainly in the field of NMR. Stanimira Naydenova, chemist in education, was natural leader in research of chemical structure and physicochemical properties. Nina Shonova studied mainly the interactions between liquid crystal cells and electronic circuits. Isak Bivas and Marin Mitov developed as leading researchers in elastic properties of thermotropic liquid crystals and later on in elastic properties of lyotropic liquid crystals and membranes.