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Journal ArticleDOI

Landau Theory of Nematic-Smectic-A Transition in a Liquid Crystal Mixture

01 Apr 1998-Molecular Crystals and Liquid Crystals (Taylor & Francis Group)-Vol. 312, Iss: 1, pp 157-164
TL;DR: In this paper, the first or second order nature of the nematic-smectic-A phase transition is explored and general Landau theory for coupled orientational, translational order parameters and concentration is developed.
Abstract: Binary mixtures of HBAB {p-[(p-hexyloxy-benzylidene)-amino] benzonitrile} and CBOOA [N-p-cyanibenzylidene-p-n-octyloxyaniline] exhibit a two phase region where both smectic-A and nematic phase coexists. The reason for this two phase region is discussed by means of Landau formalism. The problem of the first or second order nature of the nematic-smectic-A phase transition is explored. General Landau theory for coupled orientational, translational order parameters and concentration is developed.
Citations
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Journal ArticleDOI
TL;DR: In this paper, the effect of nonmesogenic solute on the nematic-smectic-A (NA) transition is examined within the Landau phenomenological theory, and the effects of non mesogenic solutes on the Frank elastic constants are also discussed.
Abstract: The effect of nonmesogenic solute on the nematic-smectic-A (NA) transition is examined within the Landau phenomenological theory. When nonmesogenic solute are added to a mesogenic compound consisting of both nematic and smectic-A phases, the NA transition temperature is depressed and a two phase region is formed due to the presence of the impurities of the solute. Decreasing the nonmesogenic solute to the pure compound, the first order NA transition becomes second order at the tricritical point in Landau approximation. The effects of nonmesogenic solute on the Frank elastic constants are also discussed.

21 citations

Journal ArticleDOI
TL;DR: The predictive capability of the present model for determining the tricritical point of a binary mixture displaying the N-SmA transition has been demonstrated by testing with reported phase diagrams sharing both phases.
Abstract: We propose a phenomenological model to describe the tricritical behavior of the nematic to smectic-A (N-SmA) phase transition in liquid crystal mixture. To describe the mesophase transitions in binary mixture, nematic and smectic order parameters have been coupled with the concentration. We show that a tricritical point on the N-SmA phase transition line can be achieved under certain conditions. The predictive capability of the present model for determining the tricritical point of a binary mixture displaying the N-SmA transition has been demonstrated by testing with reported phase diagrams sharing both phases.

8 citations

Journal ArticleDOI
TL;DR: In this article, the authors examined the effect of pressure on the nematic to smectic-A N-SmA transition within the Landau phenomenological theory and found that the theoretical predictions were in good qualitative agreement with experimental results.
Abstract: We examine the effect of pressure on the nematic to smectic-A N–SmA) transition within the Landau phenomenological theory. The influence of pressure on the N–SmA transition is discussed by varying the coupling between the orientational and translational order parameters. The possibility of the tricritical point at the N–SmA transition is discussed in a phenomenological way. The theoretical predictions are found to be in good qualitative agreement with experimental results.

6 citations

Journal ArticleDOI
TL;DR: In this article, a Landau-de-Gennes phenomenological model is proposed to describe the pressure induced smectic A-nematic phase transition, and the influence of pressure on the phase transition is discussed for varying coupling between orientational and translational order parameter with pressure.
Abstract: We propose a Landau-de Gennes phenomenological model to describe the pressure induced smectic A-nematic phase transition. The influence of pressure on smectic A-nematic phase transitions are discussed for varying coupling between orientational and translational order parameter with pressure. Increasing the pressure, the first order nematic-smectic A transition becomes second order at a tricritical point which agrees fairly well with available experimental results.

4 citations

Journal Article
TL;DR: In this article, the phase transition temperatures of Nematic liquid crystal and Cholesteric liquid crystal in different proportions were measured using differential scanning calorimetry (DSC) technique.
Abstract: Liquid crystals are characterized by high molecular orientation order in their mesomorphic states. The mixture of liquid crystals influences the molecular orientation of liquid crystal compound consequently affecting their physical properties. In this paper, the main focus is on the study of the mixtures of Nematic liquid crystal and Cholesteric liquid crystal in different proportions. We have used Differential scanning calorimetry (DSC) technique to measure the Phase transition temperatures. Fourier Transform Infrared Spectroscopy (FTIR) and Ultraviolet–Visible (UV) spectroscopy are used to analyze the relative concentration of liquid crystals in the mixtures and their spatial distribution.The values of pitch for Cholesteric liquid crystal and the mixtures were calculated from ordinary refractive indices. Because of its low phase transition temperatures and less requirement of energy, the mixture of Cholesteric chloride with Cholesteryl oleate in 30%+70% proportion holds promise in the optical as well as non-optical applications of liquid crystals.

2 citations

References
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Journal ArticleDOI
TL;DR: The role of the phase in the second order smectic A↔ nematic transition is similar to the role of phase functions in superconductors as mentioned in this paper, where twist and bend distortions correspond to magnetic fields.

705 citations

Journal ArticleDOI
TL;DR: The superconducting phase transition is predicted to be weakly first order, because of effects of the intrinsic fluctuating magnetic field, according to a Wilson-Fisher $\ensuremath{\epsilon}$expansion analysis, as well as a generalized mean-field calculation appropriate to a type-I superconductor.
Abstract: The superconducting phase transition is predicted to be weakly first order, because of effects of the intrinsic fluctuating magnetic field, according to a Wilson-Fisher $\ensuremath{\epsilon}$-expansion analysis, as well as a generalized mean-field calculation appropriate to a type-I superconductor. Similar results hold for the phase transition from a smectic-$A$ to a nematic liquid crystal.

653 citations

Journal ArticleDOI
P. E. Cladis1
TL;DR: The nematic phase occurs at both a higher and a lower temperature than the smectic phase as mentioned in this paper, and measurements of the bend elastic constant as a function of concentration are presented.
Abstract: The nematic-smectic-$A$ transition temperature of mixtures of HBAB {$p$-[($p$-hexyloxybenzylidene)-amino]benzonitrile} and CBOOA [N-$p$-cyanobenzylidene-$p\ensuremath{-}n$-octyloxyaniline] becomes multivalued with increasing concentration of HBAB. The nematic phase occurs at both a higher and a lower temperature than the smectic phase. Measurements of the bend elastic constant as a function of concentration are presented.

321 citations

Journal ArticleDOI
TL;DR: In this paper, an adiabatic scanning calorimeter has been used to study the thermal behavior of the liquid-crystal octylcyanobiphenyl (8CB) in the temperature range between 10 and 50°C.
Abstract: An adiabatic scanning calorimeter has been used to study the thermal behavior of the liquid-crystal octylcyanobiphenyl (8CB) in the temperature range between 10 and 50\ifmmode^\circ\else\textdegree\fi{}C. The solid---to---smectic-$A$ ($\mathrm{KA}$), the smectic-$A$---to---nematic ($\mathrm{AN}$), as well as the nematic-to-isotropic (NI) phase transitions, which fall in this temperature range, have been investigated in great detail. From our measuring procedure the enthalpy behavior (including latent heats) as well as the heat capacity have been obtained. For the KA transition the latent heat was 25.7\ifmmode\pm\else\textpm\fi{}1.0 kJ/mol and for the NI transition it was 612\ifmmode\pm\else\textpm\fi{}5 J/mol. Within the resolution of our experiment we find that the $\mathrm{AN}$ transition is a continuous one. For the latent heat, if any, we arrive at an upper limit of 0.4 J/mol (or 1.4\ifmmode\times\else\texttimes\fi{}${10}^{\ensuremath{-}3}$ J/g). The observed anomaly in the heat capacity for the $\mathrm{AN}$ transition is not consistent with a nearly logarithmic singularity as predicted by the $\mathrm{XY}$ model, instead we obtain a critical exponent $\ensuremath{\alpha}={\ensuremath{\alpha}}^{\ensuremath{'}}=0.31\ifmmode\pm\else\textpm\fi{}0.03$. This result is consistent with the anisotropic scaling relation ${\ensuremath{ u}}_{\ensuremath{\parallel}}+2{\ensuremath{ u}}_{\ensuremath{\perp}}=2\ensuremath{-}\ensuremath{\alpha}$. The pretransitional effects near the NI transition are in qualitative agreement with the hypothesis of quasitricritical behavior.

174 citations