Influence of Pressure on Smectic A-Nematic Phase Transition
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.
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TL;DR: In this article, a tricritical point (TCP) composition at the second order SmA to N transition has been found for the binary mixtures of 8OCB and 9OCB.
Abstract: Modulated differential scanning calorimetry (MDSC) has been used to obtain specific heat measurements on octyloxycyanobiphenyl (8OCB), octylcyanobiphenyl (8CB) and nonyloxycyanobiphenyl (9OCB) liquid crystals and on several binary mixtures of 8OCB + 9OCB and 8CB + 9OCB. The order of the mesophase transitions, smectic A(SmA) to nematic(N) and N to isotropic (I) on pure components and on binary mixtures has been studied and, in addition, both binary mesophase diagrams have been built. For each set of mixtures, there exists a tricritical point (TCP) composition at the SmA–N transition. The TCP compositions have been found to be X9OCB = 0.63 for the system 8OCB + 9OCB and X9OCB = 0.42 for the system 8CB + 9OCB. In addition, the specific heat
critical exponents (α) through second order SmA to N transition have been obtained between 8OCB(or 8CB) and the TCP composition for the two sets of binary mixtures. When these α-values were plotted against the normalised nematic range, a common and uniform crossover trend was found. Indeed, this fact suggests a uniform behaviour in terms of the McMillan ratio for the nCB and nOCB series of liquid crystals. Moreover, for these compounds there exists a common value of (TAN/TNI)TCP of 0.99 and also a value of (TAN/TNI)3D-XY of about 0.96.
48 citations
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
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
TL;DR: The Oonk's method is extended in order to account for second-order phase transitions and allows performing calculations of the tricritical temperature.
Abstract: A complete thermodynamic analysis on four two-component phase diagrams between liquid crystals belonging to the nCB and nOCB series of compounds, the so-called cyanobiphenyls, has been performed through the Oonk's equal Gibbs energy method. The binary systems dealt with in this paper show as a common feature the existence of a tricritical point at the SmA-to-N phase transition, all of which reported elsewhere. As a singular finding of the work proposed in this paper, the Oonk's method is extended in order to account for second-order phase transitions. Likewise, this extension allows performing calculations of the tricritical temperature.
3 citations
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TL;DR: In this article, the Maier-Saupe model with an orientational order parameter is extended to the smectic $A$ phase by introducing a new order parameter, the amplitude of a density wave in the direction of the nematic preferred axis.
Abstract: The Maier-Saupe model of the nematic phase with an orientational order parameter is extended to the smectic $A$ phase by introducing a new order parameter, the amplitude of a density wave in the direction of the nematic preferred axis. Self-consistent equations for the two order parameters are derived from an anisotropic model interaction and are solved numerically. We calculate the order parameters, the entropy, and the specific heat as a function of temperature for several values of dimensionless interaction strength $\ensuremath{\alpha}$ for the smectic $A$ phase. The transition temperatures plotted versus $\ensuremath{\alpha}$ provide a theoretical phase diagram which resembles experimental plots of transition temperature versus alkyl chain length for homologous series of compounds. The model qualitatively reproduces chemical trends in transition entropies. Experiments are suggested to measure the order parameters in the smectic $A$ phase.
873 citations
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
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
TL;DR: In this paper, it was shown that the critical properties of the two systems are the same, and therefore the phase transition from smectic A to nematic will always be at least weakly first order.
116 citations
TL;DR: The theory of translational and orientational melting with application to liquid crystals is presented in this article in a manner analogous to that of Kirkwood and Monroe, and the theory is applied to liquid crystal crystallography.
106 citations