共查询到20条相似文献,搜索用时 156 毫秒
1.
Ashwani Kumar Singh Amir Iqbal Upendra Bahadur Singh Roman S. Dabrowski 《Phase Transitions》2018,91(8):811-820
Thermodynamic and electro-optical characterization of a ferroelectric liquid crystalline material, namely ((S) (+) 4-(1-methylheptyloxy) phenyl 4′-octyloxybiphenyl-4-carboxylate) possessing paraelectric SmA*, ferroelectric SmC*, hexatic SmBh* and SmI* phases has been carried out. Phase identification has been done by optical and thermodynamic studies. Switching parameters viz. spontaneous polarization, switching time and rotational viscosity have been determined. The spontaneous polarization has been found to increase with decreasing temperature in SmC* phase. The switching time is found of the order of few milliseconds. 相似文献
2.
We present the results based on the electro-optic and dielectric properties of silica nanoparticle (SNP) doped ferroelectric liquid crystal (FLC) in SmC* phase. Switching time, spontaneous polarization and rotational viscosity decreases with increase in the silica concentration. An improvement in switching time after doping the silica nanoparticle is due to enhancement in anchoring energy exist between silica nanoparticle and ferroelectric liquid crystal. We noticed that the dielectric permittivity and dielectric strength decreases with increasing the concentration of silica nanoparticle in SmC* phase. Relaxation frequency increases with increasing the silica concentration and temperature in SmC* and decreases as we approaches towards transition temperature. 相似文献
3.
Cherfi Y Hemine J Douali R Beldjoudi N Ismaili M Leblond JM Legrand C Daoudi A 《The European physical journal. E, Soft matter》2010,33(4):335-342
Linear and non-linear dielectric measurements were carried out on a ferroelectric liquid crystal stabilized by an anisotropic
polymer network. The polymerization process was achieved at room temperature. It was performed from an achiral monomer in
the ferroelectric chiral smectic C phase, exhibiting a very short helical pitch and a large polarization. The linear and non-linear
dielectric spectroscopy were also completed by textural morphology as well as structural and ferroelectric characterizations.
All these measurements were carried out on a pure ferroelectric liquid crystal material and on composite films containing
two polymer concentrations. The increase of the polymer network density leads to a decrease of the dielectric strength determined
in the linear and non-linear dielectric spectroscopy. The complementarity between the linear and non-linear dielectric measurements
and their confrontation with a theoretical model allowed the simultaneous determination of some physical parameters such as
macroscopic polarization, rotational viscosity and twist elastic energy. We also discuss the effect of the polymer network
density on the obtained physical parameters. 相似文献
4.
Ghosh S Nayek P Roy SK Gangopadhyay R Rahaman Molla M Majumder TP 《The European physical journal. E, Soft matter》2011,34(4):35-6
A detailed comparative study of the dielectric and electro-optical properties of a ferroelectric liquid crystal (FLC) and
FLC after having doped with conducting polymer Poly (3,4-ethylenedioxythiophene) (PEDOT) nanotubes is done. The electro-optic
study reveals a lower electrical response time, rotational viscosity and spontaneous polarization in the FLC/PEDOT nanocomposite
system. By fitting the capacitance with voltage in a Preisach model, four dipolar species in both FLC and composites system
have been obtained. The orientation of the four dipolar species in the composites system is such that the effective dipole
moment in the transverse direction of the FLC molecule is less than that in FLC compound. 相似文献
5.
We report the results of dielectric and electro-optical properties of ferroelectric liquid crystal (FLC), Felix 17/100, exhibiting chiral smectic C phase and dye dispersed FLCs. The polarization measurement on pristine and dye dispersed FLC mixture shows decrease in the value of polarization, indicating the distribution of dye dipole in a direction opposite to the orientation of FLC molecule. The rotational viscosity also decreases accordingly as shown by the measurement of response time. Dielectric measurement shows existence of two relaxation modes both in pure FLC and dye dispersed FLC. The relaxation strength of Goldstone mode decreases with the dispersion of dye and the relaxation frequency of this mode shifts towards the high-frequency side. The second relaxation mode arises due to the formation of domains at the surface interface. The dispersion of dye into FLC suppresses the domains. 相似文献
6.
R. Manohar Kamal Kumar Pandey Satya Prakash Yadav Abhishek Kumar Srivastava Abhishek Kumar Misra 《哲学杂志》2013,93(34):4529-4539
The effect is reported of surface anchoring on various electro-optical parameters of a pure ferroelectric liquid crystal (FLC) and five mixtures with different concentrations of dye. The Anthraquinone D5 dye was used as guest entity, whereas Felix 17-000 was used as host in this investigation. The presence of dye molecules in the FLC dramatically affects the electro-optical properties compared with those of the pure system. Electro-optical parameters such as spontaneous polarization and rotational viscosity not only change with the addition of dye but they are also strongly dependent on the concentration of dye in pure FLC. The effect of dye molecules on the anchoring energy of the pure FLC system was also investigated. Due to strong anchoring energy on FLC substrate, its effect on response time was also studied. An improvement in the contrast ratio after dye doping was observed. The value of spontaneous polarization increases due to addition of dye, suggesting that molecular alignment improves, which is very useful from the application point of view. 相似文献
7.
《Current Applied Physics》2009,9(3):605-609
We report here the dielectric relaxation spectroscopy and electro-optical properties of a ferroelectric liquid crystal (FLC) CB470 (R) and isomeric mixtures containing CB470 (R) and its optical isomer CB480 (S) in two different concentrations. We have studied with two isomeric mixtures: mixing CB470 (R) and CB480 (S) in the ratio 95:5 (w/w) and 90:10 (w/w). With increase of percentage of CB480 (S) in the mixture the spontaneous polarization (PS) value has been decreased due to cancellation of a part of the dipolar contribution, since the direction of PS of the two isomers are in opposite direction. The tilt angles of the pure FLC materials and the isomeric mixtures remain almost unchanged. The dielectric strength of Goldstone mode is almost proportional to the spontaneous polarization (PS). An additional collective mode has been observed in the SmC1 phase due to the formation of domain with large periodicity in pure FLC material and in one of the isomeric mixtures by unwinding the helical structures, which is known as domain mode. The existence of domain mode has been studied extensively with the variation of PS in the isomeric mixtures. The result has been discussed. 相似文献
8.
Li Zhao Zhiwei Hu Chang‐Yang Kuo Tun‐Wen Pi Maw‐Kuen Wu Liu Hao Tjeng Alexander C. Komarek 《固体物理学:研究快报》2015,9(12):730-734
From magnetic susceptibility, dielectric permittivity, electric polarization and specific heat measurements we discover spin‐induced ferroelectricity and magnetoelectric coupling in Mn3TeO6 and observe two successive magnetic transitions at low temperatures. A non‐ferroelectric intermediate magnetic state occurs below 23 K and a multiferroic ground state emerges below 21 K. Moreover, Mn3TeO6 is a candidate for a multiferroic material where two types of incommensurate spin structures, cycloidal and helical, coexist. Theoretically, both spin substructures may contribute to the macro electric polarization via different mechanisms. This could open new ways of manipulating the ferroelectric polarization in a multiferroic material. (© 2015 WILEY‐VCH Verlag GmbH &Co. KGaA, Weinheim) 相似文献
9.
A.G. Khachaturyan 《Journal of Physics and Chemistry of Solids》1975,36(10):1055-1061
A nematic liquid crystalline phase is considered whose rod-like non-centrosymmetric molecules possess a permanent dipole moment. This phase is a “liquid ferroelectric” if all the molecules are oriented along the same “preferred” direction. It is shown that a liquid ferroelectric can not exist in a homogeneous nematic state. It is transformed into a more stable helical structure (the vector of the spontaneous polarization of such a structure rotates aroung the helical axis). There is a variety of domain structures for the specific case when the anisotropy coefficient of the polarization is equal to zero. Since each elementary dipole moment is rigidly bound to its molecule, the “preferred” alignment direction of the rod-like molecules as well as the polarization vector rotates with respect to the same axis in a helical manner. Therefore a nematic phase with a nonzero spontaneous polarization has a cholesteric structure. Its helical pitch is determined by the geometric size of the sample, the absolute value of the spontaneous polarization, and the elastic moduli. Apparently, we can consider some cholesteric phases to be liquid ferroelectrics with helical domain structure. 相似文献
10.
Daoudi A Dubois F Legrand C Laux V Buisine JM 《The European physical journal. E, Soft matter》2003,12(4):573-580
Comparative electro-optical measurements have been made on a ferroelectric liquid crystal (FLC) in surface stabilized geometry and confined to an ellipsoidal cavity within a polymer matrix. The static and dynamic electro-optical characteristics were measured for both systems and show qualitatively similar behaviours. A fast switching and important bistability were observed and characterized as a function of the applied electric field strength. The switching time between the two stable states of the surface stabilized cell was found to be longer than that found for the composite films. We argue that the faster switching dynamic of the FLC in cavities is due to the enhance of the rotational mobility of the molecules, probably (and partly) because of the soft anchoring character of the molecules at the cavity walls. Using a collective switching model in the high field regime, which assume a linear coupling between the spontaneous polarization and the local cavity electric field, we give an estimate of the rotational viscosity of the FLC molecules in the droplets.Received: 5 October 2003, Published online: 5 February 2004PACS:
61.30.Pq Microconfined liquid crystals: droplets, cylinders, randomly confined liquid crystals, polymer dispersed liquid crystals, and porous systems - 61.30.Hn Surface phenomena: alignment, anchoring, anchoring transitions, surface-induced layering, surface-induced ordering, wetting, prewetting transitions, and wetting transitions - 77.80.Fm Switching phenomena 相似文献
11.
Samriti Khosla 《Journal of Physics and Chemistry of Solids》2004,65(6):1165-1175
The dielectric spectroscopy of a short pitch and high spontaneous polarization ferroelectric liquid crystal mixture and its guest-host derivatives with different wt/wt ratio of anthraquinone blue dichroic dye has been studied over a wide frequency range of 50 Hz-1 MHz. The increase in dye concentration results in the decrease of the permittivity of the material in the SmC* phase, however, an opposite effect is observed in the SmA phase. The influence of bias voltage on the dielectric parameters has also been investigated. A new relaxation mode has been observed with a relaxation frequency of ∼300 kHz and dielectric strength of ∼5 at room temperature. 相似文献
12.
A. Mikułko M. Marzec M. Wierzejska R. Douali CH. Legrand S. Wróbel 《Phase Transitions》2013,86(6-7):585-594
In this article the physical properties of hexatic phases of three substances MHPNBC, FOOPP and FNHPP have been studied by differential scanning calorimetry, texture observation and dielectric spectroscopy. Experimental results are discussed from the point of view of existing theories. It is interesting that two of the substances studied, the FOOPP and FNHPP, exhibit enhanced spontaneous polarization in the highly ordered SmI* phase and show a jump of the spontaneous polarization in the vicinity of the SmC*–SmI* transition. In the SmI* phase of FOOPP a very high value of spontaneous polarization of the order of 530?nC?cm?2 was found. Based on the results obtained the macroscopic and microscopic properties of the hexatic phases are discussed. 相似文献
13.
Anamika Pramanik Malay Kumar Das Vĕra Hamplová Miroslav Kašpar Alexej Bubnov 《Phase Transitions》2015,88(7):745-757
The effect of several polar ester linkage groups incorporated in the molecular core of a chiral lactic acid derivative on self-assembling properties has been investigated by polarizing optical microscopy, small angle X-ray diffraction, differential scanning calorimetry, optical and electro--optical studies. The compound possesses the paraelectric smectic A* (SmA*) and ferroelectric smectic C* (SmC*) phases over a broad temperature range. Mesomorphic behaviour, spontaneous polarization, birefringence, optical transmission, dielectric anisotropy and structural properties of the self-assembled chiral material have been determined. The obtained results are discussed and compared with that of other liquid crystalline materials. Experimentally determined spontaneous polarization and tilt angle values are also used to elucidate the nature of SmC* to SmA* phase transition. The effect of polar ester linkages in the molecular core has also been discussed. 相似文献
14.
Effect of magnetic nanoparticles (nickel ferrite) doping on the dielectric and electro-optical properties of a ferroelectric liquid crystal mixture has been studied. In a doped ferroelectric liquid crystal mixture, dispersion of a small amount (0.25 wt.%) of nickel ferrite nanoparticles decreases the polarization and improves the response time compared to an undoped mixture. The significant changes in the polarization and response time are explained on the basis of dipole–dipole interaction and anchoring phenomena. Dielectric permittivity also increases with increasing the temperature of the SmC* phase and shows a reduction in dielectric loss in a doped sample. A Goldstone mode is clearly observed at ~200 and ~500 Hz in an undoped and a doped sample, respectively. 相似文献
15.
Four racemic mixtures were synthesized and characterized. Their mesomorphic properties, such as phase transitions temperatures and enthalpies, were measured by a polarizing optical microscope and differential scanning calorimetry. The influence of one racemic mixture on the properties of the OAFLC mixture W-1000 was studied. The results show a wide temperature range of the SmCA* phase in this new mixture. The helical pitch was measured by spectrophotometry method. The electro-optical properties of the mixture were also presented and discussed. 相似文献
16.
The decay width, forward-backward asymmetry and lepton longitudinal and transversal polarization for the exclusive B → K*ℓ+ℓ− decay in a two Higgs doublet model are computed. It is shown that all these quantities are very effective tools for establishing new physics. 相似文献
17.
Xiang-Wu Zhang Chunsheng Wang A. John Appleby Frank E. Little 《Solid State Ionics》2002,150(3-4):383-389
Mixed-conducting lithium-ion doped emeraldine polyaniline (PAni)–polyethylene oxide (PEO) blends have been developed to achieve an optimal electronic–ionic conductivity balance in nano-tin composite anodes. Electrochemical evaluation was performed on the anodes with differing electrode preparation procedures, doping methods and PEO contents. Results indicate that both good electronic and ionic conductivity in the binder are required for rapid lithium insertion/extraction and low polarization. This doped PAni–PEO polymer blend is an attractive binder for high capacity composite anodes with low polarization. 相似文献
18.
19.
D. G. Baranov V. A. Dergachev Yu. F. Gagarin A. P. Lobakov V. A. Lukin V. I. Lyagushin A. V. Solov''ev E. A. Yakubovskii 《Radiation measurements》1995,25(1-4):301-306
Energy spectra of subiron (Sc---Cr) and iron nuclei in the range 40–210 MeV/n have been measured and subiron to iron abundance ratio was determined from a study of a polyethyleneterephthalate (Lavsan) detector exposed in 1984–1985 during a year on the Salyut-7 space station. The ratio measured is 0.9 in the energy range 170–210 MeV/n that confirms previous data. The value differs from that 0.4-0.5 measured in interplanetary space. The ratio is 0.45 in the range 40–110 MeV/n. The peculiarities observed are discussed. 相似文献
20.
采用格胞模型,定义在格胞中心上的极化序参量.选用双轴性并具有横向电矩的分子作用势,求得系统的自由能,得到自发极化强度的大小和螺旋变化螺距的表达式.计算了DOBAMBC和3M2CPOOB等4种典型SmC*相液晶的自发极化强度大小和螺距随温度的变化及其受分子横向电矩的影响,结果与实验相符.表明SmC*相的自发极化强度主要产生于分子的双轴性和横向电矩.
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