Phase Transition and Abnormal Behavior of a Nematic Liquid Crystal in Benzene

Kundu, Shyamal Kumar; Okudaira, Shun; Kosuge, Masanori; Shinyashiki, Naoki; Yagihara, Shin

doi:10.1021/jp903391z

Cited by 7 publications

(7 citation statements)

References 29 publications

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“…9͑b͔͒, not to mention that this MD generally occurs at a much higher frequency range. On the other hand, although crystallized 6CB molecules in the crystalline phase can also give rise to dielectric relaxation, the relaxation intensity is generally several decimals even for pure LC, 36,37 which is far smaller than that in the present case. Accordingly, the mechanism due to the rotation of 6CB molecules in the bulk solution or in the crystalline phase can be ruled out.…”

Section: H Rotation Of 6cb Moleculescontrasting

confidence: 67%

“…It is shown that the transition temperature of isotropic-nematic transition inside the LC droplets is strongly dependent on solute concentration. 19 Furthermore, in a similar LC solution composed of 5CB and benzene, 36,37 the bulklike isotropicnematic phase transition only shows up at high LC concentration range ͑Ͼ70 wt %͒ and the transition temperature also strongly depends on LC concentration; whereas at low LC concentration range, the crystalline-isotropic phase transition ͑melting͒ temperature is almost independent of LC concentration. According to these facts, the concentration independence of transition temperature shown in Fig.…”

Section: Resultsmentioning

confidence: 96%

“…36,37 The recent study 36 showed that even at low weight fraction of 5CB ͑30%͒, apparent dielectric relaxation due to the rotation of 5CB molecules in the bulk solution still showed up for 5CB/benzene mixture. In the present case, the highest weight fraction of 6CB is 18.40%, thus the rotation of 6CB molecules in the bulk solution cannot give rise to such high ⌬ ͓mostly bigger than 5, see Fig.…”

Section: H Rotation Of 6cb Moleculesmentioning

confidence: 99%

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Liquid crystalline phase in ethanol suspension of anisometric 4-cyano-4-n-hexylbiphenyl microcrystals: Witnessed by dielectric spectroscopy

Chen

Nozaki

2010

The Journal of Chemical Physics

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The suspensions of 4-cyano-4-n-hexylbiphenyl ͑6CB͒ anisometric microcrystal were obtained by quenching homogeneous 6CB/ethanol mixtures with different 6CB concentrations. Such suspensions were strongly suggested from the differential scanning calorimetry examinations and the image observations of the samples during the quench and heating processes. The crystallization process for the mixtures with higher 6CB concentration looked like the isotropic-nematic phase transition of bulk liquid crystal. Dielectric measurement was carried out on the mixtures during the heating process after quench. Distinct dielectric relaxation was observed in the frequency range between kHz and 100 kHz, which exhibited obvious dependence on temperature and 6CB concentration. Curve fitting on the complex conductivity spectra indicates that three Debye type relaxations exist in this narrow frequency range. Based on the dependences of relaxation parameters on temperature and 6CB concentration, the possible relaxation mechanisms and the phase conformation of the mixtures were discussed. It was concluded that the relaxations, from high to low relaxation frequency, originate from the Maxwell-Wagner polarization, the rotation of 6CB microcrystal around its long axis, and the reorientation of 6CB microcrystal around its short axis, respectively. It was also confirmed that the quenched 6CB/ethanol mixtures show isotropic-nematic phase transition with the increase of 6CB concentration.

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Section: H Rotation Of 6cb Moleculescontrasting

confidence: 67%

Section: Resultsmentioning

confidence: 96%

Section: H Rotation Of 6cb Moleculesmentioning

confidence: 99%

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Liquid crystalline phase in ethanol suspension of anisometric 4-cyano-4-n-hexylbiphenyl microcrystals: Witnessed by dielectric spectroscopy

Chen

Nozaki

2010

The Journal of Chemical Physics

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“…For a rodlike LC addition of 3%, benzene suppresses the nematic−isotropic temperature by ∼15 °C. 33 With a bent-core LC host, even a small concentration of an alkane or xylene as the second component reduces the clearing point (isotropic−LC phase-transition temperature) by about 10 °C. 29,34 A large decrease in the clearing point was again seen for mixtures of a discotic compound with dodecane.…”

Section: Resultsmentioning

confidence: 99%

Competition between Anisometric and Aliphatic Entities: An Unusual Phase Sequence with the Induction of a Phase in an n-Alkane–Liquid Crystal Binary System

et al. 2014

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In this work, we demonstrate two important features that arise out of introducing a liquid-crystalline (LC) compound into the rotator phase matrix and the consequent competition between the anisometric segments of the LC moieties and the aliphatic units. First, we show that the change in the structural character of the mixed medium depends on which of the entities forms the minority concentration: in the case of this being the alkane, the two components of the binary system are nanophase segregated, whereas if the LC molecules are present in a small concentration, then the layered structure merely gets roughened without any segregation. The second and more significant result of the calorimetric and X-ray experiments, at low LC concentrations, is the induction of a rotator phase that leads to unusual phase sequence not reported hitherto. Possible scenarios for the molecular arrangement are discussed. A Landau model is also presented that explains some of the observed features.

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“…non-interacting, non-mesogenic and non-polar solvent) -as has Kundu et al [14]. Usol'tseva et al has observed that dissolving a thermotropic liquid crystal compound in a non-polar organic solvent produces ferroelectric liquid crystals with remarkable properties [15].…”

Section: Introductionmentioning

confidence: 95%

Semi-empirical analysis on electronic spectra and ultraviolet stability of nematic liquid crystals: effect of solvent and substituent

Praveen¹,

Ojha²

2011

Liquid Crystals

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To cite this article: P. Lakshmi Praveen & Durga P. Ojha (2011) Semi-empirical analysis on electronic spectra and ultraviolet stability of nematic liquid crystals: effect of solvent and substituent, Liquid Crystals, 38:8, 963-970, A semi-empirical analysis has been carried out on two nematic liquid crystals, 4-cyanophenyl-4 -n-pentylbenzoate (CPPB) and 4-cyanophenyl-4 -n-pentoxybenzoate (CPPOB), using the CNDO/S + CI and INDO/S + CI methods. These methods have been applied to simulate and analyse the electronic structures, spectra and ultraviolet (UV) stability of the systems. Phase stability of the systems has also been studied based on molecular charge distribution. The electronic transitions, absorption wavelength, HOMO and LUMO energies are calculated. Furthermore, UV stability of the molecules is discussed in the light of absorption wavelength and electronic transition oscillator strength (f ). The effect of solvent and substituent on these factors is discussed. A comparison among different solvents is also made. These absorption spectra will provide a valuable database for further computational analysis and the other experimental investigations. IntroductionLiquid crystals represent a class of complex fluids that has opened many doors for us to learn a great deal about molecular interactions [1], phase behaviour, transitions and the art of soft condensed matter. These molecular fluids show specific optical properties due to the anisotropy of molecular organisation [2]. This anisotropy plays an important role in applications of the electrical effect, display devices, spatial modulators, etc. The bulk order in these materials has profound control on the way light [3] and electricity behave in the material. A unique insight into this behaviour provides not only information about the particular material under consideration, but also about the global properties of anisotropic fluids and their relationships to other chemical structures and/or physical phenomena.Despite their various applications [4][5][6][7], liquid crystals (LCs) belonging to the 4-cyanophenyl-4 -n-alkylbenzoate (CPnB) homologous series and their composites are less studied than those from cyanobiphenyl series. The simulation of electronic spectra by computational chemistry tools is particularly appealing since a large number of methods have been elaborated and employed to calculate the molecular vertical excitation energies, absorption wavelength and oscillator strength of electronic transitions.In view of this, methods based on Time Dependent Density Functional Theory (TDDFT)

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Phase Transition and Abnormal Behavior of a Nematic Liquid Crystal in Benzene

Cited by 7 publications

References 29 publications

Liquid crystalline phase in ethanol suspension of anisometric 4-cyano-4-n-hexylbiphenyl microcrystals: Witnessed by dielectric spectroscopy

Liquid crystalline phase in ethanol suspension of anisometric 4-cyano-4-n-hexylbiphenyl microcrystals: Witnessed by dielectric spectroscopy

Competition between Anisometric and Aliphatic Entities: An Unusual Phase Sequence with the Induction of a Phase in an n-Alkane–Liquid Crystal Binary System

Semi-empirical analysis on electronic spectra and ultraviolet stability of nematic liquid crystals: effect of solvent and substituent

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