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1
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Application of Modified Interference Wedge Method in Measurements of Indices of Refraction and Birefringence of Nematic Liquid Crystals

100%
Kowiorski K., Kędzierski J., Raszewski Z., Kojdecki M., Herman J., Miszczyk E., Piecek W.
Acta Physica Polonica A
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2013
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vol. 124
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issue 6
946-948
EN
Wedge cell filled with a homogeneously oriented nematic liquid crystal was exploited as an interference wedge to measuring indices of refraction. Interference fringes from the wedge were observed in polarised light in reflection or transmission mode of a polarisation microscope to determining ordinary and extraordinary indices of refraction or birefringence (i.e. anisotropy of both indices). The interference fringes close to wedge apex were uniform and could be well described in two-beam interference approximation. The refractive indices were computed with using simple formulae involving only distances between subsequent fringes in a cell filled with the liquid crystal and an empty reference cell. Several new highly-birefringent nematic mixtures produced in the Military University of Technology were investigated. The 6CHBT nematic was used as the reference material.
2
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Study of Refractive Indices, Density and Order Parameters of Two Nematogens and Their Eutectic Mixture

63%
Datta Sarkar S., Choudhury B.
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issue 4
665-669
EN
The compounds 5-pentyl-2-(4'-cyanophenyl) pyrimidine [CM 7035] and 4-n-butyl-4'-ethoxytolan [PTP4O2] and mixtures of different mole fractions of them show nematic phase with supercooling effect. From the phase diagram the equimolar mixture is found to be the eutectic mixture. Temperature variation of the density and refractive indices (n_{o}, n_{e}) of the pure compounds and their eutectic mixture have been reported here. The density and birefringence values of the eutectic mixture are found to be less than that of pure compounds. However the average refractive index values of eutectic mixture almost coincide with those of CM 7035 which are much less than those of PTP4O2. The refractive indices and density values have been analyzed to obtain the orientational order parameters. Experimental order parameter values of the pure compounds and the eutectic mixture are compared with theoretical Maier-Saupe values. The possible reasons for disagreement between theoretical and experimental values for the pure compounds are discussed. The agreement between theoretical and experimental order parameters are fairly good for the eutectic mixture.
3
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Behavior of Co^{2+} Cations in the Aqueous and Alcoholic Solution of CoCl_2·6H_2O

63%
Petkova P., Nedkov V.
Acta Physica Polonica A
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2013
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vol. 123
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issue 2
207-208
EN
We investigated the optical properties of Co^{2+} cations in the aqueous and alcoholic solution of CoCl_2·6H_2O at room temperature. We measured the absorption spectra of these solutions in the spectral region 395-800 nm. The Racah parameters and the exchange integrals of the aqueous complex [Co(H_2O)_6]^{2+} are calculated. The parameters D_{t} and D_{s} are also calculated on the basis of our experimental data. The parameters δ σ and δπ which are connected with the symmetry of this complex are also determined.
4
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An Optical Study to Estimate Orientational Order Parameter on Some Benzylideneaminophenylbenzoate Liquid Crystals

51%
Subhan C., Jeevan Kumar R., Panduranga P., Jayashreeand B., Fakruddin K.
Acta Physica Polonica A
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2016
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vol. 129
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issue 3
284-288
EN
The birefringence technique has been used for the evaluation of order parameter in the nematic phase along with the density measurements, which are needed for the calculation of molecular polarizabilities of the compounds. Birefringence and density studies have been carried out on the three liquid crystalline compounds viz.(1) (E)-4-((4-hexyloxy)benzylidene)amino)phenyl 4-butoxybenzoate(2) (E)-4-((4-hexyloxy)benzylidene)amino)phenyl 4-(decycloxy)benzoate and(3) (E)-4-((4-hexyloxy)benzylidene)amino)phenyl 4-(tridecycloxy)benzoate.Using birefringence and density data the molecular polarizabilities are evaluated by two different internal field models due to Vuks and Neugebauer. The mean molecular polarizability of the compounds is also evaluated by employing modified Lippincott δ-function model. The results reveal that both the theoretical and experimental values obtained are very near to each other.
5
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Effect of Temperature on the Refractive Indices of Liquid Crystals and Validation of a Modified Four-Parameter Model

51%
Thingujam K., Sarkar S., Choudhury B., Bhattacharjee A.
Acta Physica Polonica A
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2012
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vol. 122
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issue 4
754-757
EN
The variation of refractive indices with temperature of three pure nematogenic compounds 5OCB, CPHB and 6CHBT were studied experimentally using thin prism technique. The refractive indices n_{o} and n_{e} were measured using 633 nm lines from a He-Ne laser. A modified four-parameter model was taken which is based on the Vuks equation describing the effect of temperature on the refractive indices of liquid crystals. In this paper we report the variation of refractive indices of these three liquid crystals with temperature, using the thin prism method. The variation in birefringence was determined experimentally. The variation in refractive indices and birefringence were also fitted theoretically using the modified Vuks equation. On comparison, the theoretically fitted values show close agreement with the experimental values.
6
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Room Temperature Ferroelectric Mixture of Chiral and Achiral Thioesters

51%
Czerwiec J., Ossowska-Chruściel M., Chruściel J., Wróbel S.
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issue 4
549-552
EN
Dielectric properties of the mixture of two thioester compounds: 4-8-alkoxy-benzoate-thio-carboxyl S-4-pentyl-phenyl (8OS5), (s)-4-(1-methyl-heptyloxy)biphenyl-4-thio-carboksyl 4-9-alkil-phenyl (MHOBS9) are presented. The chiral compound exhibits nematic (N*) and ferroelectric smectic C* phase (SmC*). The achiral compound shows N, SmA and monotropic SmC and SmB phases. the mixture of both compounds of 0.5 molar fraction shows SmC* in the wider temperature range than pure MHOBS9. The mixture was studied using frequency domain dielectric spectroscopy. Dielectric measurements for the SmC* phase of the mixture revealed Goldstone mode at higher frequencies and Maxwell-Wagner relaxation at low frequencies.
7
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Dielectric Properties of Ferroelectric Liquid Crystals with Diversified Molecular Structure

51%
Czerwiec J., Dąbrowski R., Żurowska M., Ziobro D., Wróbel S.
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issue 4
553-556
EN
Mesomorphic, thermodynamic, electro-optic and dielectric properties of three homologues of fluorosubstituted esters are described. Full chemical names of these compounds are as follows: (S)-(+)-4-(1-metyl-hepty-loksy)benzoate-(6-penta-fluoro-propano-ynloxyhex-1-oxy)-biphenyl-4-yl (in short 2F6BBiOC8), (S)-(+)-4-(1-metyl-hepty-loksy)benzoate-(6-nona-fluoro-pentano-yloxyhex-1-oxy)-biphenyl-4-yl (in short 4F6BBiOC8), (S)-(+)-4-(1-metyl-hepty-loksy)benzoate-(6-trideca-fluoro-heptano-yloxyhex-1-oxy)-biphenyl-4-yl (in short 6F6BBiOC8). The compounds exhibit ferroelectric smectic C* phase between crystalline and isotropic phase. Only one compound (6F6BBiOC8) shows antiferroelectric phase (SmC*_{A}) observed by dielectric spectroscopy, but the range of this phase is narrow of about 2°. All three compounds exhibit in the SmC* phase Goldstone mode and Maxwell-Wagner relaxation hidden in the conductivity contribution at low frequencies, whereas in the SmC* _{A} phase two anti-ferroelectric modes (AFM1) and (AFM2) contribute to the dielectric spectrum. The compounds were studied using differential scanning calorimetric, frequency domain dielectric spectroscopy, and reversal currents method to determine spontaneous polarization.
8
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Characterization of Optical and Photoelectrical Properties of ZnO Crystals

51%
Onufrijevs P., Serevičius T., Scajev P., Manolis G., Medvids A., Chernyak L., Kuokstis E., Yang C., Jarasiunas K.
Acta Physica Polonica A
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2011
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vol. 119
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issue 2
274-276
EN
We characterized optical and photoelectrical properties of undoped and Ga-doped ZnO layers differently grown on sapphire substrates by using complementary optical methods. Different stimulated emission threshold values for ZnO epitaxial layers grown by pulsed laser deposition and MBE methods were attributed to crystalline quality of the layers and the growth method used. Different carrier lifetimes in various ZnO epitaxial layers are explained by defect-related and intrinsic mechanisms of recombination.
9
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Evaluation of Optical Properties of Ag, Cu, and Co Nanoparticles Synthesized in Organic Medium

51%
Kaminskienė Ž., Prosyčevas I., Stonkutė J., Guobienė A.
Acta Physica Polonica A
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2013
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vol. 123
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issue 1
111-114
EN
The surface plasmon resonance evaluation of colloidal metal nanoparticles, synthesized in organic medium, is reported in this work. Metal salts were dissolved in dioxane/AOT solution and reduced by hydrazine hydrate under vigorous stirring. Optical properties of obtained colloidal nanoparticles were investigated by UV-VIS spectroscopy. Theoretical predictions of optical properties of metal nanoparticles were made by means of the Mie theory and the Drude free-electron model. Geometrical parameters and distribution of metal nanoparticles in colloidal solutions were characterized by atomic force microscopy. The results show that Ag, Cu, and Co nanoparticles, synthesized in organic medium distinguish plasmonic properties. Surface plasmon resonance bands were obtained in all cases: Ag - at 430 nm, Cu - at 570 nm, Co - at 350 nm (SPR1) and 430 nm (SPR2). Comparing theoretical evaluation of nanoparticles size with atomic force microscopy analysis, we can assume that our calculations are accurate. It was found that dominating nanoparticles diameter in Ag colloidal solution is ≈ 150 nm, in Cu colloidal solution is ≈ 70 - 80 nm and in Co colloidal solution is ≈ 150 nm. It can be concluded that nanoparticles with enhanced plasmonic properties synthesized in organic medium can be widely used in order to increase efficiency of various optical elements.
10
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Equimolecular Mixture of Calamitic and Bent-Core Thiobenzoates

51%
Chruściel J., Wantusiak B., Ossowska-Chruściel M.
Acta Physica Polonica A
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2012
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vol. 122
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issue 2
375-377
EN
This article reports on the new results on phase transitions, mesomorphic and electro-optical properties of new equimolecular mixture of calamitic and bent-core thiobenzoates. Two following liquid crystals were the components of the binary mixture: (S)-(+)-4-(1-methylheptyloxy)biphenyl 4'-octylthiobenzoate (MHOBS8) having rode-like, calamitic-chiral molecules possessing among others ferroelectric smectic C (SmC*) and bis [4-(4'-octylphenylthiocarbonyl)phenyl] isophtalates from a homologous series of banana-shaped thioesters, referred to as IFOS8, where n = 8 denoted the number of carbon atoms in terminal alkyl chains in both mesogens, synthesized by us. The IFOS8 compound has two enantiotropic phases: B2 with antiferroelectric order and B6. The mesomorphic properties were investigated by means of three complementary methods: differential scanning calorimetry, polarized light optical microscopy, and transmitted light intensity. Electro-optical measurements were also carried out.
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