Density Measurements in the Nematic and Isotropic Phases of 5CB and Dilute Solutions of Tetraethylmethane in 5CB

Oweimreen, G. A.; Shihab, A. K.; Halhouli, K.; Sikander, S. F.

doi:10.1080/00268948608071767

Cited by 34 publications

(27 citation statements)

References 14 publications

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“…For n =12, this curve is shown in Fig. 1 together with data on MBBA, 4-n-pentyl-4'-cyanobiphenyl (5CB) [17][18][19][20], and 4 n- It should be noted that the present theory diA'ers in the underlying physics from the approach which attributes the lowering of (T, -T*)/T, from its MS mean field value as resulting from Auctuation eAects intrinsic to the MS Hamiltonian [24,25]. Since Auctuation is inherently a higher-order effect (than the mean field approximation), it is logical to argue that one must first incorporate the lower-order eAects that should be present, such as the isotropic, density-dependent component of the interaction, before assessing the eff'ects due to fluctuations.…”

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Nematic-isotropic phase transition: An extended mean field theory

1993

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The small magnitude of (T, -T )/T"where T, is the nematic-isotropic phase transition temperature and T denotes the virtual transition temperature, has been a long-standing puzzle in the physics of liquid crystals. We show that by extending the mean field theory to include the isotropic, densitydependent component of the molecular interaction the magnitudes of both (T, -T*)/T, and the density change at the transition automatically become in accord with the experimental values. In addition, the theory yields a value of dT, /dp, where p denotes pressure, that is on the same order as the experiment. [4], but the incorporation of that extra part also materially affects the character of the N-I transition.In particular, the predicted magnitude of (T, -T*)/T, is lowered to the experimental range, while at the same time the theory also yields the right magnitudes both for the density variation across the N-I transition as well as for the variation of T, with pressure.

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confidence: 99%

Nematic-isotropic phase transition: An extended mean field theory

1993

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“…The existente of a two-phase region is consistent with the first order nature of the nematic-to-isotropic transition. From visual [3-7] and density [8,9] studies the phase diagram shown in Fig. …”

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confidence: 99%

“…The existente of a two-phase region is consistent with the first order nature of the nematic-to-isotropic transition. From visual [3][4][5][6][7] and density [8,9] studies the phase diagram shown in Fig. 1 a non-mesomorphic-nematogenic solvent mixture at moderately low solute mole fractions x 2 (0.005 = x 2 _< 0.06) where T* (= T/TNI ) is the reduced temperature and TN~ is the nematic-to-isotropic transition temperature of the "pure" liquid-crystalline solvent.…”

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confidence: 99%

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Phase diagrams from spin probe studies for binary mixtures of non-mesomorphic solutes in 5CB

1995

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The effect of low concentrations of a non-mesomorphic solute impurity on the nematicto-isotropic transition of 4-cyano-4'-n-pentylbiphenyl (5CB), has been investigated by ESR spectroscopy, using predeuterated-2,2,6,6-tetramethyl-4-piperidone-N-oxide (PD-Tempone), at mole fractions of the order of 10 -5, as a probe. It has been found that at such low mole fractions PD-Tempone simply probes the nematic-to-isotropic transition without observably perturbing it. This fast approach relies on the fact that a smaller coupling constant is obtained for the spin probe in the orientationally ordered nematic phase relative to the isotropic phase. The method has been further refined in this study by the use of an especially designed sample holder which, in conjunction with a temperature control and monitoring system, allowed control of the temperature of the sample to within _+0.02~ Additionally measurements were made, for each solute, at several solute mole fractions within the range from 0.01 to 0.07. The results were used to obtain fin and ti1, the moduli of the slopes of the nematic and isotropic boundary lines respectively in the reduced nematic-to-isotropic transition temperature (T*) versus solute mole fraction (x2) diagrams. The non-mesomorphic solutes used in this study are n-nonane, 3,3-diethylpentane, tetrapropyltin and tetrabutyltin. lntroductionThe addition of a non-rod-like solute impurity to a nematogenic solvent leads, with few exceptions [1,2] where complexation with the nematogen is suspected, to a depression of the nematic-to-isotropic transition temperature and the formation of a two-phase region. The existente of a two-phase region is consistent with the first order nature of the nematic-to-isotropic transition. From visual [3-7] and density [8,9] studies the phase diagram shown in Fig.

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“…However, experiments clearly show the pretransitional anomaly of physical properties associated with the critical exponent α [4,[38][39][40][41][42][43][44][45][46] where p(T) and cp(T) are the density and the specific heat respectively. Coefficients di, αi, D, and A denote amplitudes.…”

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confidence: 99%

The Fluid-Like and Critical Behavior of the Isotropic-Nematic Transition Appearing in Linear and Non-linear Dielectric Studies

2000

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A short review of literature and the authors' experimental results for the pretransitional behavior in the isotropic phase of nematogens is given. The paper also presents new results of non-linear dielectric effect and dielectric permittivity measurements in the broad temperature range. Results obtained show significant advantages of non-linear dielectric effect and dielectric permittivity for studying pretransitional properties in liquid crystalline materials. The paper contains a comprehensive comparison of the experiment with predictions of the mean-field model and the fluid-like description. The presented analysis strongly supports the image of the isotropic phase as a complex liquid resulting from vicinity of the fluid-like, "nematic-isotropic", critical point.

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Density Measurements in the Nematic and Isotropic Phases of 5CB and Dilute Solutions of Tetraethylmethane in 5CB

Cited by 34 publications

References 14 publications

Nematic-isotropic phase transition: An extended mean field theory

Nematic-isotropic phase transition: An extended mean field theory

Phase diagrams from spin probe studies for binary mixtures of non-mesomorphic solutes in 5CB

The Fluid-Like and Critical Behavior of the Isotropic-Nematic Transition Appearing in Linear and Non-linear Dielectric Studies

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