Katalin Fodor-Csorba

Bio: Katalin Fodor-Csorba is an academic researcher from Hungarian Academy of Sciences. The author has contributed to research in topics: Liquid crystal & Phase (matter). The author has an hindex of 23, co-authored 108 publications receiving 2194 citations.

Giant Flexoelectricity of Bent-Core Nematic Liquid Crystals

Abstract: Flexoelectricity is a coupling between orientational deformation and electric polarization. We present a direct method for measuring the flexoelectric coefficients of nematic liquid crystals (NLCs) via the electric current produced by periodic mechanical flexing of the NLC's bounding surfaces. This method is suitable for measuring the response of bent-core liquid crystals, which are expected to demonstrate a much larger flexoelectric effect than traditional, calamitic liquid crystals. Our results reveal that not only is the bend flexoelectric coefficient of bent-core NLCs gigantic (more than 3 orders of magnitude larger than in calamitics) but also it is much larger than would be expected from microscopic models based on molecular geometry. Thus, bent-core nematic materials can form the basis of a technological breakthrough for conversion between mechanical and electrical energy.

Giant flexoelectricity of bent-core nematic liquid crystals

Abstract: Flexoelectricity is a coupling between orientational deformation and electric polarization. We present a direct method for measuring the flexoelectric coefficients of nematic liquid crystals (NLCs) via the electric current produced by periodic mechanical flexing of the NLC's bounding surfaces. This method is suitable for measuring the response of bent-core liquid crystals, which are expected to demonstrate a much larger flexoelectric effect than traditional, calamitic liquid crystals. Our results reveal that not only is the bend flexoelectric coefficient of bent-core NLCs gigantic (more than 3 orders of magnitude larger than in calamitics) but also it is much larger than would be expected from microscopic models based on molecular geometry. Thus, bent-core nematic materials can form the basis of a technological breakthrough for conversion between mechanical and electrical energy.

Structural changes in the 6CHBT liquid crystal doped with spherical, rodlike, and chainlike magnetic particles.

Abstract: In this work the 4-(trans- 4'-n -hexylcyclohexyl)-isothiocyanatobenzene (6CHBT) liquid crystal was doped with differently shaped magnetite nanoparticles. The structural changes were observed by capacitance measurements and showed significant influence of the shape and size of the magnetic particles on the magnetic Freedericksz transition. For the volume concentration phi= 2 x 10(-4) of the magnetic particles, the critical magnetic field was established for the pure liquid crystal, and for liquid crystals doped with spherical, chainlike, and rodlike magnetic particles. The influence of the magnetic field depends on the type of anchoring, which is characterized by the density of anchoring energy and by the initial orientation between the liquid crystal molecules and the magnetic moment of the magnetic particles. The experimental results indicated soft anchoring in the case of spherical magnetic particles and rigid anchoring in the case of rodlike and chainlike magnetic particles, with parallel initial orientation between the magnetic moments of the magnetic particles and director.

Nonstandard electroconvection in a bent-core nematic liquid crystal.

Abstract: We characterize three nonstandard electrohydrodynamic instabilities in nematic liquid crystals composed of bent-core molecules In addition to their shape, another important attribute of this material is that the anisotropy in the electrical conductivity changes sign as the frequency of the applied electric field changes These instabilities do not appear to fit within the standard model for electroconvection The first instability creates a pattern with stripes parallel to the initial director orientation, with a wavelength about equal to the separation of the cell plates The next is the previously reported prewavy instability The third instability is optically and dynamically identical to the prewavy instability, but is distinguished by different threshold behavior

Ester‐type banana‐shaped monomers and investigations of their electro‐optical properties

Abstract: New banana-shaped monomers 1a–1f, based on the 1,3-phenylene bis{4-[4′-(alkenyloxy)benzoyloxy]}benzoate bent structure were prepared. The central 1,3-phenylene ring was either unsubstituted (1a, 1b) or had a 2-methyl substituent (1c, 1d) or a 4-chloro substituent (1e, 1f), respectively. The occurrence of mesophases greatly depended on the chemical structure of the banana-shaped molecules. Whilst 1,3-phenylene bis{4-[4′-(10-undecenyloxy)benzoyloxy]}benzoate (1b, acronym Pbis11BB) formed a monotropic B2 phase, the 4-chloro derivatives showed conventional nematic and SmC phases. In contrast, the 2-methyl derivatives did not form any kind of mesophases. MOPAC/AM1 semi-empirical calculations allowed evaluation of the value and orientation of the electric dipole vectors and of the twist angles of the central phenyl ring with respect to the outer rings. Electro-optical investigations showed that the B2 phase of 1b was antiferroelectric with a 45° tilt angle between 91–75 °C (P = 320 nC · cm−2) and a switching time in the range of 50 μs in a E = 15 V · μm−1 field. Synthetic route for the preparation of monomers 1a–1f.

Bent-core liquid crystals: polar order, superstructural chirality and spontaneous desymmetrisation in soft matter systems

Abstract: An overview on the recent developments in the field of liquid crystalline bent-core molecules (so-called banana liquid crystals) is given. After some basic issues, dealing with general aspects of the systematisation of the mesophases, development of polar order and chirality in this class of LC systems and explaining some general structure–property relationships, we focus on fascinating new developments in this field, such as modulated, undulated and columnar phases, so-called B7 phases, phase biaxiality, ferroelectric and antiferroelectric polar order in smectic and columnar phases, amplification and switching of chirality and the spontaneous formation of superstructural and supramolecular chirality.

Bent-Core Liquid Crystals: Their Mysterious and Attractive World

Abstract: Structures and properties of liquid crystalline phases formed by bent-core molecules are reviewed. At least eight phases designated as B1–B8 have been found, being unambiguously distinguished from phases formed by usual calamitic molecules due to a number of remarkable peculiarities. In addition to B1–B8 phases, smectic A-like phases and biaxial nematic phases formed by bent-core molecules are also reviewed. The most attractive aspects of this new class of liquid crystals are in polarity and chirality, despite being formed from achiral molecules. The bent-core mesogens are the first ferroelectric and antiferroelectric liquid crystals realized without introducing chirality. Spontaneous chiral deracemization at microscopic and macroscopic levels occurs and is controllable. Moreover, achiral bent-core molecules enhance system chirality. The interplay between polarity and chirality provides chiral nonlinear optic effects. Further interesting phenomena related to polarity and chirality are also reviewed.

The renaissance of H/D exchange.

Abstract: The increasing demand for stable isotopically labeled compounds has led to an increased interest in H/D-exchange reactions at carbon centers. Today deuterium-labeled compounds are used as internal standards in mass spectrometry or to help elucidate mechanistic theories. Access to these deuterated compounds takes place significantly more efficiently and more cost effectively by exchange of hydrogen by deuterium in the target molecule than by classical synthesis. This Review will concentrate on the preparative application of the H/D-exchange reaction in the preparation of deuterium-labeled compounds. Advances over the last ten years are brought together and critically evaluated.

Stable Dispersions of Fullerenes, C60 and C70, in Water. Preparation and Characterization

Abstract: Stable aqueous dispersions of fullerenes, C60 and C70, were prepared by simply injecting into water a saturated solution of fullerene in tetrahydofuran (THF), followed by THF removal by purging gaseous nitrogen. To our knowledge, this is the first report of the stable dispersion of C70 in water. Fullerenes are dispersed as monodisperse clusters in water, 60 nm in diameter. High resolution transmission electron microscopy revealed the polycrystalline nature of the cluster. The preparation of the dispersion is very easy to perform, and the dispersions thus obtained are of excellent colloidal stability even though no stabilizing agent is used. It was found that the surface of the cluster is negatively charged and the electrostatic repulsion between the negatively charged cluster surfaces is important for the stability of the dispersions.