Publications (20)53.84 Total impact
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Dataset: Lyotropic chromonic liquid crystal semiconductors for water-solution processable organic electronics
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Article: Elasticity of lyotropic chromonic liquid crystals probed by director reorientation in a magnetic field.
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ABSTRACT: Using a magnetic Frederiks transition technique, we measure the temperature and concentration dependences of splay K1, twist K2, and bend K3 elastic constants for the lyotropic chromonic liquid crystal sunset yellow formed through noncovalent reversible aggregation of organic molecules in water. K1 and K3 are comparable to each other and are an order of magnitude higher than K2. At higher concentrations and lower temperatures, K1 and the ratios K1/K3 and K1/K2 increase, which is attributed to elongation of self-assembled lyotropic chromonic liquid crystal aggregates, a feature not found in conventional thermotropic and lyotropic liquid crystals formed by covalently bound units of a fixed length.Physical Review Letters 07/2012; 109(3):037801. · 7.37 Impact Factor -
Article: Square colloidal lattices and pair interaction in a binary system of quadrupolar nematic colloids.
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ABSTRACT: Spherical colloidal particles with normal and tangential surface director alignment in a nematic liquid crystal induce elastic quadrupoles of opposite signs that attract one another along and perpendicular to the director. We utilize this unique angular profile of the mixed quadrupolar interaction to build 2D crystals with square lattices by laser tweezers.Physical Review E 04/2011; 83(4 Pt 1):041709. · 2.26 Impact Factor -
Article: Lyotropic chromonic liquid crystal semiconductors for water-solution processable organic electronics
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ABSTRACT: We propose lyotropic chromonic liquid crystals (LCLCs) as a distinct class of materials for organic electronics. In water, the chromonic molecules stack on top of each other into elongated aggregates that form orientationally ordered phases. The aligned aggregated structure is preserved when the material is deposited onto a substrate and dried. The dried LCLC films show a strongly anisotropic electric conductivity of semiconductor type. The field-effect carrier mobility measured along the molecular aggregates in unoptimized films of LCLC V20 is 0.03 cm^2 V^(-1) s^(-1). Easy processibility, low cost, and high mobility demonstrate the potential of LCLCs for microelectronic applications.01/2011; -
Article: Surface alignment and anchoring transitions in nematic lyotropic chromonic liquid crystal.
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ABSTRACT: The surface alignment of lyotropic chromonic liquid crystals can not only be planar (tangential) but also homeotropic, with self-assembled aggregates perpendicular to the substrate, as demonstrated by mapping optical retardation and by three-dimensional imaging of the director field. With time, the homeotropic nematic undergoes a transition into a tangential state. The anchoring transition is discontinuous and can be described by a double-well anchoring potential with two minima corresponding to tangential and homeotropic orientation.Physical Review Letters 07/2010; 105(1):017801. · 7.37 Impact Factor -
Article: Effects of Anthraquinone Dye Aggregation on Selective Reflection Spectra of Cholesteric Liquid Crystal
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ABSTRACT: The formation of supramolecular aggregates of anthraquinone dye N,N′-(4-methylphenyl)-1,4-diaminoanthraquinone (AQ) is shown to be clearly manifested in temperature-dependent selective reflection spectra of cholesteric solvents containing AQ as a non-mesogenic dopant. Using cholesteric matrices of different chemical nature (based on cholesterol esters or nematics with chiral dopants), one can distinguish between interactions of a solvent with individual AQ molecules and AQ aggregates, as well as between the aggregation and precipitation of AQ. The calculated relative birefringence data demonstrate the effects of AQ aggregates on the optical anisotropy and the orientational order in the systems under study.Molecular Crystals and Liquid Crystals 01/2008; 496(1):202-211. · 0.58 Impact Factor -
Article: Chromonic nematic phase and scalar order parameter of indanthrone derivative with ionic additives
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ABSTRACT: We investigate influence of different ionic additives on the phase behaviour and scalar order parameter of lyotropic chromonic nematic liquid crystals formed by the molecules representing derivatives of indanthrone. KI, (NH4)2SO4 and NaCl salts increase biphasic nematic region on the temperature-concentration phase diagram, whereas the scalar orientational order parameter is hardly sensitive to their presence. We suggest that these changes are attributed to increase in the ag-gregate length and polydispersity of the latter, while the interaction between ag-gregates remains unaffected. The Na2SO4 salt lowers anomalously the measured value of the scalar order parameter to 0.42, for which the nematic phase should not exist. We address this anomaly to modification of the shape of chromonic aggregates due to growing of side chains within the rod-like aggregates. The NH4Cl salt does not affect the phase diagram and the scalar order parameter of Blue 250 chromonematic.Ukrainian Journal of Physical Optics. 01/2008; -
Article: Coexistence of two colloidal crystals at the nematic-liquid-crystal-air interface.
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ABSTRACT: Glycerol droplets at a nematic-liquid-crystal-air interface form two different lattices--hexagonal and dense quasihexagonal--which are separated by the energy barrier and can coexist. Director distortions around each droplet form an elastic dipole. The first order transition between the two lattices is driven by a reduction of the dipole-dipole repulsion through reorientation of these dipoles. The elastic-capillary attraction is essential for the both lattices. The effect has a many-body origin.Physical Review Letters 03/2007; 98(5):057801. · 7.37 Impact Factor -
Article: Optical anisotropy of uniformly aligned planar surfactant lyotropic nematic doped with hemoglobin
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ABSTRACT: The system under study is a nematic phase of lyotropic surfactant liquid crystal, cetylpyridinium chloride/hexanol/brine. Optical birefringence measured for well-aligned surfactant nematic (surfonematic) is weakly dependent on the light wavelength within the studied spectral region (500–700 nm) and its absolute value is about 6*10-4. Doping of the surfonematic by hemoglobin (1.5% by weight) does not affect the birefringence value, suggesting that the hemoglobin does not produce its own birefringence and does not affect the scalar orienta-tional order parameter of the surfonematic matrix. The absorption coefficients of hemoglobin in the surfonematic matrix exhibit a broad band shifted several tens of nanometres towards longer wavelengths, when compare to the spectrum of hemoglobin dissolved in water. The latter indicates that the hemoglobin residues form molecular complexes with the surfactant molecules. Weak (app.2*10-2) linear dichroism of hemoglobin at the wavelengths corresponding to light absorption by oxygen bonds gives the estimation of the orientational scalar order parameter of hemoglobin molecules in well-aligned surfonematic matrix (app. 10-2)Ukrainian Journal of Physical Optics. 01/2007; -
Article: Polarizing Properties of Functional Optical Films Based on Lyotropic Chromonic Liquid Crystals
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ABSTRACT: We report results of the optical characterization of dried thin films obtained from the well-aligned nematic phase of a lyotropic chromonic liquid crystal (LCLC) by two different deposition techniques. The first one, the electrostatic layer-by-layer deposition technique, was used to prepare aligned LCLC films of a nanometer thickness in the form of a monomolecular layer and multi-layered stack. The second technique is the direct deposition technique. The films' optical characteristics such as dispersion of the light absorption indices, birefringence, polarizing efficiency, contrast ratio, transmittance of unpolarized light, were measured and compared with the correspondent characteristics of a cell filled with nematic solution of the same LCLC material.Molecular Crystals and Liquid Crystals. 01/2007; 467(June):181-194. -
Article: Hypothesis of Dye Aggregation in a Nematic Liquid Crystal: From Experiment to a Model of the Enhanced Light-Director Interaction
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ABSTRACT: We report experimental and theoretical arguments showing that the effect of strong enhancement of the light-induced director reorientation in a nematic liquid crystal doped with anthraquinone dye molecules (Jánossy effect) can be related to their aggregation. The torque on the director is due to dependence of the entropy of the aggregate subsystem on the electric field vector relative to the director.Molecular Crystals and Liquid Crystals 09/2006; 454:145/[547]-156/[558]. · 0.58 Impact Factor -
Article: Sign inversion of the optical torque on the nematic director enhanced by anthraquinone dye dopants stable to the light action
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ABSTRACT: By analyzing the total and on-axis transmittance of the laser beam we studied the enhanced light-induced director reorientation (Jánossy effect) in a nematic liquid crystal doped with anthraquinone dye molecules that do not have photoinduced conformational transformations. The obtained dependence on the angle between the light polarization E and the initial director n0 shows: first order director reorientation (DR) transition with hysteresis for E ⟂ n0; second order reversible DR transition with the extremely low threshold intensity for E ∥ n0; sign inversion of the nonlinear refractive index and DR in the intermediate geometry. The data suggest a presence of two different kinds of dipoles in the system: those absorbing light and those giving rise to the nonlinear refractive index. (© 2006 by Astro, Ltd. Published exclusively by WILEY-VCH Verlag GmbH & Co. KGaA)Laser Physics Letters 07/2006; 3(11):531 - 535. · 9.97 Impact Factor -
Article: Enhanced light-induced director reorientation and dye aggregation in a nematic liquid crystal
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ABSTRACT: Our experimental and theoretical data suggest that the strong enhancement of light-induced director reorientation in a dye-doped nematic liquid crystal can be caused by aggregation of the dye molecules.Functional Materials. 06/2006; 13(4):682 - 686. -
Article: Ordered droplet structures at the liquid crystal surface and elastic-capillary colloidal interactions.
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ABSTRACT: We demonstrate a variety of ordered patterns, including hexagonal structures and chains, formed by colloidal particles (droplets) at the free surface of a nematic liquid crystal (LC). The surface placement introduces a new type of particle interaction as compared to particles entirely in the LC bulk. Namely, director deformations caused by the particles lead to distortions of the interface and thus to capillary attraction. The elastic-capillary coupling is strong enough to remain relevant even at the micron-scale when its buoyancy-capillary counterpart becomes irrelevant.Physical Review Letters 10/2004; 93(11):117801. · 7.37 Impact Factor -
Article: Deformation of liquid crystal droplets under the action of an external ac electric field.
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ABSTRACT: Deformation of liquid crystal droplets suspended in liquid polymer matrix under the action of external electric field was observed in dependence of ion concentration in such system. Experimental dependence of droplet elongation vs electric field demonstrates nonmonotonous character with increase of ion concentration. The theory that provides the basic agreement with experimental observation is developed.Physical Review E 09/2001; 64(2 Pt 1):021706. · 2.26 Impact Factor -
Article: Crystal structure in nematic emulsion.
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ABSTRACT: We describe the experimental observation of a crystal structure formed by glycerol droplets suspended in a nematic liquid crystal. The structure exhibits a high density hexagonal ordering. We have experimentally observed a noticeable interaction between droplets with tangential boundary conditions. Within the scope of known models we discuss the nature of appropriate mechanisms of the interaction.Physical Review Letters 09/2001; 87(7):075504. · 7.37 Impact Factor -
Article: Deformation and instability of nematic drops in an external electric field
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ABSTRACT: The behavior of nematic liquid-crystal drops freely suspended in an isotropic liquid polymer exposed to an external electric field was studied. A giant deformation was observed for the drop. As the field intensity increased, its equilibrium shape took the form of a prolate ellipsoid. The dependences of the shape and critical fields on the concentration of ions in the polymer liquid were established. A plausible theoretical explanation is suggested for the observed effect. The experimental dependence of drop size on the electric-field strength is analyzed, and the conditions for the loss of drop stability are determined.JETP Letters 01/2000; 71(6):262-265. · 1.35 Impact Factor -
Article: Non-Debye screening of a surface charge and a bulk-ion-controlled anchoring transition in a nematic liquid crystal.
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ABSTRACT: We study the anchoring mechanism due to substrate-adsorbed ions by examining a related anchoring transition. An analytical solution to the Poisson equation shows that, as their number suffices for a non-negligible anchoring contribution, the surface field is screened over some characteristic microscopic distance. It is shown both theoretically and experimentally that the critical temperature of the transition can be controlled by bulk ion density through its relation to the density of adsorbed ions.Physical review. E, Statistical physics, plasmas, fluids, and related interdisciplinary topics 12/1999; 60(5 Pt A):5580-3. -
Article: Selective light-induced desorption: The mechanism of photoalignment of liquid crystals at adsorbing solid surfaces
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ABSTRACT: We demonstrate experimentally that bare solid surfaces with adsorbed organic molecules can orient liquid crystals after UV light irradiation. The detailed structure and behavior of the surface-adsorbed molecules are not important to the effect: just their UV light absorption should depend on their orientation. The only requirement to the solid substrates is their transparency to the UV light. The universal reason for the photoinduced anisotropy in such systems is that photons clean from the surface those molecules that absorb them most intensively. This is a kind of light rubbing resulting in the anisotropic ablation of the adsorbed material.http://dx.doi.org/10.1209/epl/i2006-10122-9. -
Article: Non-Debye screening of a surface charge and a bulk-ion-controlled anchoring transition in a nematic liquid crystal
[show abstract] [hide abstract]
ABSTRACT: We study the anchoring mechanism due to substrate-adsorbed ions by examining a related anchoring transition. An analytical solution to the Poisson equation shows that, as their number suffices for a non-negligible anchoring contribution, the surface field is screened over some characteristic microscopic distance. It is shown both theoretically and experimentally that the critical temperature of the transition can be controlled by bulk ion density through its relation to the density of adsorbed ions.Phys. Rev. E. 60(5).
Top co-authors
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Institutions
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2004–2012
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Kent State University
Kent, OH, USA
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1999–2008
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National Academy of Sciences of Ukraine
- Institute of Physics
Kharkiv, Kharkivs'ka Oblast', Ukraine
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