Dielectric Behaviour of Liquid Crystals

Kresse, H.

doi:10.1002/prop.19820301002

Cited by 62 publications

(16 citation statements)

References 154 publications

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“…The spectro− scopic results for 8CB seem to be more reliable, taking into account that this liquid crystal has the more ordered smectic A phase below the nematic phase. Moreover, they are in a good agreement with the values of <P 2 electron paramagnetic resonance [40] and optical birefrin− gence [41] measurements. Therefore, it is clear that the low value of the retardation factor of 8CB has to be connected with the creation of the microdomains with the nematic−like order in the broad temperature region before I−N phase tran− sition.…”

Section: Order Parametersupporting

confidence: 83%

“…The relaxation time t 0 is a hypothetical value of t for the state with vanished nematic potential at the same tempera− ture [1,2] and in our experiment it was determined through the extrapolation of the temperature dependence of the re− laxation time t measured in the isotropic phase to the tem− perature of interest in the nematic phase. Figure 8 presents the retardation factor G as a function of the reduced temperature, T red = T/T IN for 8CPB and, for comparison, the results for 8CB and 8CHBT, obtained on the basis of the data from Refs.…”

Section: Order Parametermentioning

confidence: 99%

“…The dielectric properties of these substances are of primary importance, because the electro−optical parame− ters of LCDs, such as threshold voltage, response times and multiplexing capability are strongly dependent on the aniso− tropy of dielectric permittivity. On the other hand, studies of the dielectric properties of nematic liquid crystals in the static electric/magnetic fields provide us with the information on re− lation between the dielectric anisotropy of the mesogenic sub− stance, its molecular structure and the dipole−dipole correlation leading to the self−association process [1,2]. The dielectric spectroscopy is yet a powerful tool for the study of the molecu− lar arrangement and the dynamics of the molecular rotational motions both in the mesomorphic and isotropic phases [1][2][3][4].…”

Section: Introductionmentioning

confidence: 99%

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Dielectric and orientational properties of nematogenic 4-n-octyl(4′-cyanophenyl)benzoate

Bauman

Jadżyn

Wolarz

et al. 2010

Opto-Electronics Review

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Experimental studies of the dielectric properties in the nematic and isotropic phases of 4-cyanophenyl-4′-n-octylbenzoate (8CPB) have been performed in the frequency range from 50 kHz to 100 MHz. The relaxation process related to the rotation around the short molecular axis has been analysed. The results obtained have revealed that in the vicinity of the I-N phase transition, the molecular subdiffusional rotation process occurs. It is connected with the pretransitional effects which are observed both in the static and dynamic dielectric measurements. On the basis of the temperature dependence of the relaxation time in the nematic and isotropic phases, the orientational order parameter 〈P2〉 has been determined. The values of 〈P2〉 obtained in this way have been compared with those evaluated from the measurements of the polarized electronic absorption of the dichroic dye, dissolved as guest probe in the mesogenic host.

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Section: Order Parametersupporting

confidence: 83%

Section: Order Parametermentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Dielectric and orientational properties of nematogenic 4-n-octyl(4′-cyanophenyl)benzoate

Bauman

Jadżyn

Wolarz

et al. 2010

Opto-Electronics Review

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“…The basic mixture (BM) 4-n-Alkyloxyphenyl trans-4-n-alkylcyclohexanecarboxylates seemed to be suitable because of the low melting points and no dielectric absorption u p to the MHz range (KRESSE, BUKA) : -- (KRESSE 1982) : given in Table 3. The mixture melts into the nematic phase a t about 283 K, T'SI is a t 343 K. At 293 K the shear viscosity is v2 = 120 mPa .…”

Section: 2mentioning

confidence: 99%

The development of a nematic two frequency addressing mixture

Stettin¹,

Kresse

Schäfer

1989

Cryst. Res. Technol.

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An example is given for the development of a nematic two frequency addressing mixture based on the equations for the threshold voltages, the switching times, and the dielectric relaxation. New substances have been synthesized with relaxation frequencies in the kHz range and big values of the static dielectric anisotropy at room temperature. The isotropy frequency and the relation between the high and low frequency dielectric anisotropy, respectively, are adjustable by adding of substances without a relaxation mechanism in the kHz range and with a big negative static dielectric anisotropy. The produced mixture was dielectrically investigated. Calculated and experimentally found data are in a good agreement.Es wird ein Beispiel gegeben fur die Entwicklung einer nematischen Zweifrequenzadressierbaren Mischung auf der Grundlage der Gleichungen der Schwellspannungen, der Schaltzeiten und der dielektrischen Relaxation. Neue Substanzen wurden synthetisiert mit Relaxationsfrequenzen im kHz-Bereich und grolSen statrschen diefektriscfien Anisotropien bei Raunitemperatur. Die Isotropiefrequenz uncl daniit das Verhiiltnis zwischen der statischen und der hochfrequenten dielektrischen Anisotropie kann durch Zugabe von Substanzen, die grol3e negative statische dielektrische Anisotropien besitzen und keinen Relaxationsmechanismus im kHz-Bereich zeigen, eingestellt werden. Die von uns hergestelite Mischung wurde dielektrisch untersucht. Die berechneten und die experimentell ermittelten Daterk stimmen gut iiberoin

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“…Dielectric spectroscopy is a powerful method of investigation of liquid crystals [1][2][3]. This method applied to bulk nematic and smectic-A liquid crystals studies relaxation processes of molecular origin.…”

Section: Introductionmentioning

confidence: 99%