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Dynamics of Nematogenic Molecules with Transverse Component of Dipole Moment

100%
Douali R., Czechowski G., Legrand C., Jadżyn J.
Acta Physica Polonica A
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2004
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vol. 105
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issue 4
365-371
EN
The paper presents the results of studies of the dielectric relaxation of nematic 4'-butyloxy-3-fluoro- 4-isothiocyanatotolane, performed for different values of the angle between the probing electric field E and the macroscopic orientation of the sample (the director n) forced by the magnetic field B. Due to a relatively large transverse component of the dipole moment of 4'-butyloxy- 3-fluoro-4-isothiocyanatotolane, the studies allowed one to interpret consistently the dielectric relaxation spectra connected with the molecular rotation around the long axis.
2
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Molecular Dynamics of 4-(trans-4'-n-Heptylcyclohexyl)- Isothiocyanatobenzene Studied with Dielectric Relaxation Spectroscopy

88%
Bauman D., Czechowski G., Jadżyn J., Legrand C., Douali R.
Acta Physica Polonica A
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2000
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vol. 98
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issue 1-2
71-81
EN
Dielectric relaxation study was carried out for the nematic and isotropic phases of 4-(trans-4'-n- heptylcyclohexyl)isothiocyanatobenzene in the frequency range from 100 kHz to 1 GHz. In the nematic phase two relaxation processes were recorded for the electric permittivity component measured parallel to the molecular orientation (director n) and three relaxation processes - for the perpendicular permittivity component. The strength of the nematic potential and the nematic order parameter were estimated.
3
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Anomalous Dielectric Spectra of Ferro- and Ferrielectric Liquid Crystalline Phase in MHPNBC

76%
Dubois F., Douali R., Wawrzyniak A., Legrand C., Ropa P., Wróbel S., Dąbrowski R.
Acta Physica Polonica A
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2013
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vol. 124
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issue 6
937-939
EN
MHPOBC analogue with long achiral alkyl chain has been investigated by dielectric spectroscopy studies in the wide temperature range. Low frequency dielectric spectroscopy revealed the existence of normal ferroelectric phase (in a narrow gap), two ferri- and three antiferroelectric phases in addition to paraelectric phase and alpha sub-phase. The compound studied shows exceptionally strong dependence of the dielectric permittivities on measuring electric field in the temperature range of ferro- and ferrielectric phases.
4
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Dielectric and Electrooptic Investigations of B Phases οf Banana-Shaped Thioesters

64%
Wierzejska-Adamowicz M., Ossowska-Chruściel D., Chruściel J., Douali R., Legrand C., Marzec M., Mikułko A., Sikorska A., Wróbel S.
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issue 4
557-561
EN
Electrooptic and dielectric measurements were done for B phases of two banana-shaped homologues 1,3-phenylene bis{4-[(4-nonylo-xy-benzoyl)sulfanyl]benzoate (9OSOR) and 1,3-phenylene bis{4-[(4-dodecylo-xy-benzoyl)sulfanyl]benzoate (12OSOR). Polarizing microscopy allowed to identify B_{1} phase for 9OSOR and B_{2} phase for 12OSOR on the basis of texture observation. Spontaneous polarization measurements were performed using reversal current method. The current response to applied triangular voltage shows that B_{1} phase is a ferroelectric and B_{2} phase - antiferroelectric one for which two well separated peaks were observed. Polarization for phase B_{1} of 9OSOR is rather small and its temperature dependence is unusual for ferroelectric liquid crystals - it increases with temperature. Spontaneous polarization for B_{2} phase of 12OSOR compound is of about 600 nC/cm^{2}. Dielectric spectra measured with bias field for B_{2} phase of 12OSOR show two well separated relaxation processes. In the low frequency range the relaxation process is connected with fluctuations of ferroelectric domains. The relaxation process in the high frequency range appearing also without bias field is connected with molecular reorientation. The dielectric spectra measured for B_{1} phase of 9OSOR with and without bias voltage showed only one dielectric relaxation process connected with molecular reorientation around the short axis.
5
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Polymorphism of Chiral Thioester Studied by Dielectric Spectroscopy

52%
Wawrzyniak A., Chruściel J., Douali R., Dubois F., Leblond J., Legrand C., Ossowska-Chruściel D., Marzec M., Ropa P., Czerwiec J., Wróbel S.
Acta Physica Polonica A
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2013
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vol. 124
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issue 6
933-936
EN
(S)-(+)-4'-[(4-(1-methylheptyloxycarbonylphenyl) thiocarbonylphenyl]-decyloxybenzoate (in short 10.OPOSMH) was studied by complementary methods. The substance shows rich polymorphism. In addition to ferroelectric and antiferroelectric smectic C* phases it possesses three ferrielectric sub-phases. Phase transitions between the phases were revealed by differential scanning calorimetry and static dielectric permittivity measurements. The aim of this paper was to study phase transitions and differences in dielectric spectra shown by different phases. Collective and molecular dynamics of all phases shown by 10.OPOSMH will be discussed in terms of theoretical models. Dielectric spectra of antiferroelectric phase show two characteristic dielectric relaxation modes: one connected with the molecular process (reorientation around the short axis) and the other originating from fluctuations of antiferroelectric order parameters.
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