Folyadékkristályok és polimerfilmek kölcsönhatása = Interaction between liquid crystals and polymer films

A folyadékkristály-polimer határfelületi kölcsönhatás vizsgálatában azt a fő gondolatot igyekeztünk követni, hogy a két rendszer egymás rendezettségét kölcsönösen befolyásolja. A folyadékkristály nemcsak passziv szerepet játszik a folyamatban, hanem képes a felület közelében elhelyezkedő polimerláncok rendezésére is. Ezzel magyaráztuk a felületi rendezettség memóriaeffektusát, a fotoorientáció kinetikájának függését a folyadékkristályos fázistól és a direktor-csúszás felgyorsulását az üvegesedési hőmérséklet közelében. Megadtuk a kölcsönhatás általános modelljét. A munkákban nagy szerepet kapott a fénnyel keltett jelenségek tanulmányozása. Vizsgáltuk a fénnyel keltett optikai anizotrópiát azo festékkel doppolt nagy-viszkozitású folyadékokban, fotoizomerizációval indukált fázisátmenetet valamint vizben oldott folyadékkristály cseppecskék cirkuláris fény hatására bekövetkező forgását. Ezeket a munkákat nemzetközi együttműködés keretében végeztük. | In the study of the interaction of liquid crystals with polymer layers we followed the idea that the two sub-systems influence mutually each others order. The liquid crystal does not play only a passive role in the process, but it is able to orient the polymer chains near the surface. With this suggestion we were able to explain the memory effect of the surface orientation, the dependence of the kinetics of photo-orientation on the liquid crystalline phase and the speeding up of director gliding in the vicinity of the glass transition temperature. We presented a general model for these processes. In the works a big attention was given to light-induced processes. We studied light-induced optical anisotropy in dye-doped high-viscosity fluids, phase transition induced by photo-isomerization and rotation of liquid-crystal droplets in water induced by circularly polarized light. This latter works were accomplished in international co-operations

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

Electric field-induced interfacial instability in a ferroelectric nematic liquid crystal

Studies of sessile droplets and fluid bridges of a ferroelectric nematic liquid crystal in externally applied electric fields are presented. It is found that above a threshold a fingering instability occurs, resembling to Rayleigh-type instability observed in charged droplets in electric fields or circular drop-type instabilities observed in ferromagnetic liquids in magnetic field. The frequency dependence of the threshold voltage was determined in various geometries. The nematic director and ferroelectric polarization direction was found to point along the tip of the fingers that appear to repel each other, indicating that the ferroelectric polarization is essentially parallel to the director. The results are interpreted in analogy to the Rayleigh and circular drop-type instabilities

Chiral Nematic Liquid Crystal Microlenses

Nematic liquid crystals (NLCs) of achiral molecules and racemic mixtures of chiral ones form flat films and show uniform textures between circular polarizers when suspended in sub-millimeter size grids and immersed in water. On addition of chiral dopants to the liquid crystal, the films exhibit optical textures with concentric ring patterns and radial variation of the birefringence color. Both are related to a biconvex shape of the chiral liquid crystal film; the rings are due to interference. The curvature radii of the biconvex lens array are in the range of a few millimeters. This curvature leads to a radial variation of the optical axis along the plane of the film. Such a Pancharatnam-type phase lens dominates the imaging and explains the measured focal length of about one millimeter. To our knowledge, these are the first spontaneously formed Pancharatnam devices. The unwinding of the helical structure at the grid walls drives the lens shape. The relation between the lens curvature and material properties such as helical pitch, the twist elastic constant, and the interfacial tensions, is derived. This simple, novel method for spontaneously forming microlens arrays can also be used for various sensors

Spherical-cap droplets of a photo-responsive bent liquid crystal dimer

The stays and research activities of J. Y. and F. A. in Hungary, and P. S. and A. B. in Japan are supported by the JSPS-HAS bilateral program. J. Y. was partially supported by JSPS KAKENHI Grant Number 15K17739. A. J. acknowledges financial support by NSF DMR: 1307674. Financial support from the grants NKFIH PD 121019 and FK 125134 are acknowledged.Peer reviewedPostprin

Properties of the Broad-Range Nematic Phase of a Laterally Linked H-Shaped Liquid Crystal Dimer

In search for novel nematic materials, a laterally linked H-shaped liquid crystal dimer have been synthesized and characterized. The distinct feature of the material is a very broad temperature range (about 50 oC) of the nematic phase, which is in contrast with other reported H-dimers that show predominantly smectic phases. The material exhibits interesting textural features at the scale of nanometers (presence of smectic clusters) and at the macroscopic scales. Namely, at a certain temperature, the flat samples of the material show occurrence of domain walls. These domain walls are caused by the surface anchoring transition and separate regions with differently tilted director. Both above and below this transition temperature the material represents a uniaxial nematic, as confirmed by the studies of defects in flat samples and samples with colloidal inclusions, freely suspended drops, X-ray diffraction and transmission electron microscopy.Comment: 30 pages (including Supplementary Information), 7 Figure

A Liquid Crystal Biosensor for Specific Detection of Antigens

Following the principle of the enzyme-linked immunosorbent assay (ELISA) pathogen detection method, we demonstrate specific sensing of goat Immunoglobulin G (IgG) by a nematic liquid crystal material. Sensing occurs via the visually-striking realignment of a pre-fabricated liquid crystal film, suspended in grids and coated with biotinylated lipids followed by biotinylated anti-goat IgG. Realignment occurs when the targeted goat IgG is added to the cell, but not when rat or rabbit serum IgG is added to the same surface. In principle, this method can be generalized to provide an inexpensive, fast and sensitive prefabricated sensor for any pathogen

Thermotropic Liquid Crystal-Assisted Chemical and Biological Sensors

In this review article, we analyze recent progress in the application of liquid crystal-assisted advanced functional materials for sensing biological and chemical analytes. Multiple research groups demonstrate substantial interest in liquid crystal (LC) sensing platforms, generating an increasing number of scientific articles. We review trends in implementing LC sensing techniques and identify common problems related to the stability and reliability of the sensing materials as well as to experimental set-ups. Finally, we suggest possible means of bridging scientific findings to viable and attractive LC sensor platforms