Wyniki wyszukiwania - Biblioteka Nauki

1

Dielectric relaxation behaviour of liquid crystals with opposite orientation of -COO ester group in molecular core

100%

Rutkowska J. , Perkowski P. , Piecek W. , Raszewski Z. , Kędzierski J.

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tom Vol. 16, No. 3

262-266

EN

Dielectric measurements were performed for two smectogens, being structurally analogous with the opposite space orientation of the -COO ester group in the molecular core, using a HP4192A impedance analyser. Gold coated electrode cells of different thicknesses were used. Temperature dependences of the relaxation frequency fR and the inverse of the dielectric strength Δ ε '⊥⁻¹ obtained by fitting experimental values of perpendicular components, i.e., the real ε '⊥ and the imaginary ε "⊥ parts of the complex dielectric permittivity to the Cole-Cole equation as well as the investigation of modification of relaxation processes under bias were determined for the SmC*, SmA*, and N* phases of studied compounds. One can conclude, on the basis of the above results, that dielectric relaxation processes observed by us in the studied compounds are similar to those of the soft and Goldstone mode typically observed by others in the SmC*, SmA*, and N* phases. It is concluded from a comparison of their properties with other related compounds that the link between the biphenyl moiety and –COO ester group is closely related to the stability of smectic phases.

2

Dielectric spectroscopy of liquid crystals : electrodes resistivity and connecting wires inductance influence on dielectric measurements

88%

Perkowski P.

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tom Vol. 20, No. 1

79-86

EN

Dielectric spectroscopy is a very useful experimental method for liquid crystal investigation. Electrodes made from indium tin oxide (ITO) or gold are widely used in measuring cells. During the dielectric spectroscopy measurements performed for smectic liquid crystalline mixture it was found that detection of some important relaxation modes in paraelectric SmA*, ferroelectric SmC* and antiferroelectric SmCA* phases for frequencies higher than 0.2–0.5 MHz is not possible. The measuring setup does not allow us to measure such relaxations due to its own dielectric response covering the dielectric response of liquid crystalline medium. One can observe the spurious contribution for high frequency part of the dielectric spectrum, due to non-zero resistivity of electrode material or non-zero inductivity of connecting wires. In this paper, the new model was introduced. Its final equations show how to calculate parameters of relaxations observed in liquid crystals, from dielectric response of the empty and filled measuring cell. The experimental proof of strong influence of measuring setup properties on effective (measured) values of dielectric permittivities was shown.

3

Dielectric properties of TEA-CoCl2Br2 complex

75%

Lach G. , Laskowski Ł. , Kityk I. , Tkaczyk S. W. , Świątek J. , Kapustianyk V. , Rudyk V.

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tom Vol. 26

115-121

EN

The dielectric properties of TEA-CoCl2Br2 nanocrystallites incorporated into the polymethylmethacrylate matrix within the spectral range of [wzór] Hz in the temperature range of 90K ÷ 300 K were investigated. Considerable difference of the dielectric spectra of the complex compared to the bulk crystal and to the pure polymer matrix was observed. The phenomenon of the "negative capacity" has been found. Its dependence on the mass concentration of modifying agent was investigated and explained within the appropriate molecular model.

PL

Celem pracy było zbadanie właściwości dielektrycznych kompleksu tetraetyloamono-dibromo-dichloro- kobaltu (TEACoCl2Br2) osadzonego w matrycach z polimetakrylanu metylu (PMMA). Zaobserwowano interesujące zjawiska relaksacyjne o charakterze rezonansowym (związane z ujemną rzeczywistą częścią przenikalności), występujące jedynie w próbkach złożonych z matrycy i TEACoCl2Br2.

4

Analiza relaksacji dielektrycznej w nanokompozycie PET/MWCNT

75%

Zenker M.

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tom R. 89, nr 7

318--320

PL

W artykule zaprezentowano badania metodą FDS (Frequency Domain Spectroscopy) kompozytów PET – politereftalan etylenu i PEE – poli(estro-eter) domieszkowanymi MWCNT (Multi-Walled Carbon Nanotube) – wielościennymi nanorurkami węglowymi poddanymi fluorowaniu lub modyfikacji grupami funkcyjnymi OC2H5NH2. Analizę wyników przeprowadzono za pomocą równania Havriliak’a-Negami’ego. Wyznaczono główne parametry relaksacji dielektrycznej.

EN

The paper presents research on FDS (Frequency Domain Spectroscopy) of PET and PEE composites with additions of MWCNT – Multiwall Carbon Nanotubes subjected to fluorine or modification with OC2H5NH2 function groups. The analysis of results was performed with Havriliak-Negami equation. The mail parameters of dielectric relaxation were estimated.

5

Wpływ temperatury na odpowiedź dielektryczną w dziedzinie częstotliwości papieru aramidowego impregnowanego estrem syntetycznym

63%

Zenker M.

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tom R. 94, nr 7

112--115

PL

Niniejsza publikacja dotyczy rozpoznania wpływu temperatury na parametry relaksacji dielektrycznej izolacji złożonej z papieru aramidowego (Nomex) impregnowanego estrem syntetycznym (Midel 7131). Procesy relaksacyjne badano metodą FDS (Frequency Domain Spectroscopy). Do wykonania pomiarów użyto systemu DIRANA OMICRON. Do prezentacji i analizy wyników pomiarów wykorzystano program Origin v.8.0 oraz WinFit firmy Novocontrol. Do wyznaczenia podstawowych parametrów funkcji relaksacyjnych zastosowano uogólnione równanie Havriliaka-Negamiego.

EN

This publication deals with the recognition of the influence of temperature on dielectric relaxation parameters of insulation based on aramid paper (Nomex) impregnated with synthetic ester (Midel 7131). Relaxation processes were investigated by FDS (Frequency Domain Spectroscopy). DIRANA OMICRON system was used for the measurements, while Origin v.8.0 and Novocontrol WinFit were used to present and analyze measurement results. The generalized Havriliak-Negami equation was used to determine the basic parameters of the relaxation functions.