Áramlási jelenségek folyadékkristályokban = Flux phenomena in liquid crystals

Standard homeotróp nematikus folyadékkristályokban kimértük az elektrokonvekciós mintázatok jellemzőit. Feltérképeztük a szuperponált mágneses tér ill. nyíróáramlás hatását a mintázat jellemzőire. Kidolgoztuk a mintázat lebomlásának precíz elméleti leírását, amivel a relaxációs idő hullámszámfüggését diffrakcióval megmérve kíváló egyezést találtunk. Meghatároztuk a szmektikus fázissal is rendelkező nematikusokban megfigyelt standard és nemstandard elektrokonvekciós mintázatok jellemzőit. Megmutattuk, hogy banán nematikus folyadékkristályban is fellép elektrokonvekció. Feltártuk a nematikus anizotrópiái, orientációja és az elektrokonvekciós mintázatok kialakulása és morfológiája közötti kapcsolatot. Egy általunk kidolgozott új mérési módszerrel bizonyítottuk, hogy a banán nematikus flexoelektromos együtthatója kb. 1000-szerese a hagyományos nematikusokénak. | We measured the characteristics of electroconvection patterns in standard homeotropic nematic liquid crystals. We explored the effect of superposed magnetic field or shear flow on the patterns. We worked out a rigorous theoretical description for the decay of patterns which had an excellent agreement with the wavenumber dependence of the relaxation times measured by diffraction. We determined the characteristics of the standard and nonstandard electroconvection patterns observed in nematics with smectic phases. We showed that electroconvection exists in banana nematics too. We explored the relation between the anisotropies and orientation of nematics and the existence and morphology of electroconvection patterns. We worked out a new measuring method by which we proved that the flexoelectric coefficient of a banana nematic is about 1000 times bigger than in usual nematics

Nemkirális építőelemekből álló polárosan rendezett folyadékkristályok = Mesogens with polar ordering of non-chiral building blocks

A pályázat munkatervében körvonalazott kutatási tervnek megfelelően a munka több szálon futott. Első lépést a vegyületek kémiai szintézise jelentette, ami a vizsgálni kívánt molekulaszerkezetű vegyületek megtervezését, a szintézisút kidolgozását és magát az előállítást foglalta magában. Számos esetben a vegyületekből elegyek is készültek, a fizikai folyamatok jobb megértése céljából. A pályázatból támogatott kémiai munka igen eredményes volt, nagy számú, többségében új vegyület előállítása történt meg. Ezt követték az anyagok fizikai-kémiai és fizikai módszerekkel történő vizsgálatai, amelyek során számos új eredmény és felismerés született, amit a megjelent publikációk száma és a folyóiratok minősége is demonstrál. Új, kísérleti vizsgálati módszereket és esetenként elméleti modelleket is kidolgoztunk. A pályázat támogatásával 45 cikket jelentettünk meg, amelyek kumulatív impakt faktora 103 (ebbol 5.15 IF/MFt adódik) és 96 konferenciaelőadást tartottunk nemzetközi rendezvényeken. | The research work during the project has been conducted in several directions according to the work plan of the proposal. The first step was the chemical synthesis of the desired materials which consisted of the design of the molecules, the finding of the synthetic rout and the actual production process of the compounds. In several subprojects mixtures have also been prepared from the pure compounds in order to be able to follow and understand some specific physical processes. The chemical work carried out during the project was very fruitful, a great number of mostly new substances have been synthesized. As a next step, the physico-chemical and the physical investigations followed, which have produced several original results and achievements as demonstrated by the large number of the publications and the impact factors of the journals. New experimental methods and theoretical models have been worked out. During the project 45 publications appeared with a cumulative impact factor of 103 (5.15 IF/MFt) and 96 conference contributions have been made at international meetings

Suppression of spatially periodic patterns by dc voltage

The effect of superposed dc and ac applied voltages on two types of spatially periodic instabilities in nematic liquid crystals, flexoelectric domains (FD) and electroconvection (EC), was studied. The onset characteristics, threshold voltages and critical wave vectors, were determined. We found that in general the superposition of driving with different time symmetries inhibits the pattern forming mechanisms for FD and EC as well. As a consequence the onset extends to much higher voltages than the individual dc or ac thresholds. A dc bias induced reduction of the crossover frequency from the conductive to the dielectric EC regimes and a peculiar transition between two types of flexodomains with different wavelengths were detected. Direct measurements of the change of the electrical conductivity and its anisotropy, induced by the applied dc voltage component, showed that the dc bias substantially affects both parameters. Taking into account the experimentally detected variations of the conductivity in the linear stability analysis of the underlying nemato-hydrodynamic equations, a qualitative agreement with the experimental findings on the onset behaviour of spatially periodic instabilities was obtained

Suppression of spatially periodic patterns by dc voltage

The effect of superposed dc and ac applied voltages on two types of spatially periodic instabilities in nematic liquid crystals, flexoelectric domains (FD) and electroconvection (EC), was studied. The onset characteristics, threshold voltages and critical wave vectors, were determined. We found that in general the superposition of driving with different time symmetries inhibits the pattern forming mechanisms for FD and EC as well. As a consequence the onset extends to much higher voltages than the individual dc or ac thresholds. A dc bias induced reduction of the crossover frequency from the conductive to the dielectric EC regimes and a peculiar transition between two types of flexodomains with different wavelengths were detected. Direct measurements of the change of the electrical conductivity and its anisotropy, induced by the applied dc voltage component, showed that the dc bias substantially affects both parameters. Taking into account the experimentally detected variations of the conductivity in the linear stability analysis of the underlying nemato-hydrodynamic equations, a qualitative agreement with the experimental findings on the onset behaviour of spatially periodic instabilities was obtained