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Journal ArticleDOI

Coefficient of Volume Expansion and Thermoacoustic Parameters of Alkyl‐Cyano‐Biphenyl Liquid Crystals

01 Dec 1999-Crystal Research and Technology (WILEY‐VCH Verlag)-Vol. 34, Iss: 10, pp 1299-1307
TL;DR: In this article, the coefficient of volume expansion of the alkyl-cyano-biphenyl liquid crystal CnH2n+1C6H4C 6H44.
Abstract: Dilatometric studies were performed on the nematic and isotropic phases of the homologous series of alkyl-cyano-biphenyl liquid crystals CnH2n+1C6H4C6H4. CN for n = 5 to 9. From these studies the coefficient of volume expansion (a) of the liquid crystal is estimated. Using this data a number of thermoacoustic and an harmonic parameters of the liquid crystal are evaluated. The temperature dependence of these parameters have also been investigated. All these thermoacoustic and an harmonic parameters evaluated in this case show characteristic change in the immediate vicinity of the phase transition temperature.
Citations
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Journal ArticleDOI
TL;DR: In this article, specific volume and thermal expansion studies in the nematic and isotropic phases of p-n-pentyl-p1-cyanobiphenyl (5CB) and dilute solution of the quasispherical solute tetraethyl methane were considered.

23 citations

Journal ArticleDOI
TL;DR: In this article, the ultrasonic velocity and density have been measured at different temperatures between 299 and 363 K for the pure liquid sample, poly(ethylene glycol) with average molecular mass 400 ǫg à −1 (PEG 400).
Abstract: The ultrasonic velocity and density have been measured at different temperatures between 299 and 363 K for the pure liquid sample, poly(ethylene glycol) with average molecular mass 400 g mol−1 (PEG 400). From these, isentropic compressibility (β), intermolecular free length (L f), acoustic impedance (Z), molar volume (V m), Schaff’s available volume V a(s), molar sound velocity (R a), and molar compressibility (W) have been evaluated. The variations of these parameters with the temperature of the sample have been studied. Data so obtained are employed to compute other thermodynamic parameters. Variations in various parameters with respect to temperature are discussed in the light of the results obtained.

20 citations

Journal ArticleDOI
TL;DR: In this paper, the ultrasonic velocity and density measurements on pure samples of nematics, namely, 4,4′-azoxy anisole and 4, 4′-dibutoxy azoxy benzene in dilute solutions were taken up.

15 citations

Journal ArticleDOI
TL;DR: In this paper, the structural changes arising from transition between the mesophases of liquid crystalline materials can be better understood by ultrasound in conjunction with specific volume properties, such as acoustic impedance, adiabatic compressibility, and temperature corresponding to the minimum value of ultrasonic velocity.
Abstract: The structural changes arising from transition between the mesophases of liquid crystalline materials can be better understood by ultrasound in conjunction with specific volume properties. In particular, ultrasonic studies are found to give clear information regarding the nature of the phase transition, pretransitional effects, and molecular ordering. For example, temperature corresponding to the maximum value of acoustic impedance, adiabatic compressibility, and temperature corresponding to the minimum value of ultrasonic velocity, Rao's number, order parameter, and molar compressibility, in thermotropic liquid crystals are very useful in understanding their structural behavior. In view of these facts, it was thought worthwhile to study ultrasonic velocity with data available for density measurements on pure samples of nematics, namely, 4,4′-azoxy anisole and 4,4′-dibutoxy azoxy benzene. The results of this work, are presented in this article and discussed.

8 citations

Journal ArticleDOI
TL;DR: In this paper, the synthesis, characterization and phase transition studies through density measurements on N-(pn-alkyloxybenzylidene)-p-n-butyloxyanilines, nO.O4 compounds are presented.
Abstract: This manuscript presents the synthesis, characterization and phase transition studies through density measurements on N-(p-n-alkyloxybenzylidene)-p-n-butyloxyanilines, nO.O4 compounds. The alkoxy chains with numbers n = 1 to 11, 14, 16 and 18 are synthesized and the higher homologues with n = 14 are synthesized and characterized for the first time. These compounds exhibit a variety of phase variants. The density results show that all the phase transformations are of first-order except the SmA–SmC phase transition which is of second order. The results are discussed with the body of the data available.

7 citations


Cites background from "Coefficient of Volume Expansion and..."

  • ...These transitions are usually marked by changes in various anisotropic properties, but depending on the order of the transition they may also be accompanied by changes in scalar quantities such as enthalpy content or density [1]....

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References
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Journal ArticleDOI
TL;DR: In this paper, it was shown that the velocity of sound cannot be a proper basis of comparison in any homologous series and the result of plotting the constant R against the molecular weight of members of a homology series leads to the equation R = αM + β, where α is a general constant and β a characteristic constant for any one homology.
Abstract: A study of the recently obtained data on the velocity of sound and density in liquids reveals a simple relation between these quantities namely the law, v⅓M/ρ = R where v is the velocity of sound in the liquid, M the molecular weight, ρ the density and R a constant independent of temperature. It is shown that the velocity of sound cannot be a proper basis of comparison in any homologous series. The result of plotting the constant R against the molecular weight of members of homologous series leads to the equation R = αM + β where α is a general constant and β a characteristic constant for any one homologous series. The difference in R for successive members of homologous series is a constant independent of the series and R is an additive function of the chemical structure. Values of R for hydrogen, carbon, oxygen, bromine, and chlorine are tabulated.

183 citations

Journal ArticleDOI
TL;DR: In this article, the Born and Mayer exponential expression for the repulsion between two ions has been recalculated, using these, the lattice energies and equilibrium distances between ions have been recomputed, for alkali halide crystals.
Abstract: Constants in the Born and Mayer exponential expression for the repulsion between two ions have been recalculated. Using these, the lattice energies and equilibrium distances between ions have been recomputed, for alkali halide crystals. Expressions have been derived and tested for the calculation of the compressibility and the characteristic maximum infrared frequency. The relation between these two quantities is shown to be approximated by an empirical equation proposed by Madelung.

92 citations

Journal ArticleDOI
TL;DR: In this article, an adiabatic scanning calorimeter has been used in a calorimetric investigation of alkyl-cyanobiphenyl (nCB) liquid crystals.
Abstract: An adiabatic scanning calorimeter has been used in a calorimetric investigation of alkyl-cyanobiphenyl (nCB) liquid crystals. Measurements near solid to smectic (KA), smectic A to nematic (AN) and nematic to isotropic (NI) or smectic A to isotropic (AI) phase transitions have been carried out for scanning rates as low as a few μKs−1. Results for the temperature dependence of the heat capacity as well as for the enthalpy (including latent heats) have been obtained for 8CB, 9CB, 10CB and 11CB. Latent heat values are reported for the different KA, NI and AI transitions. For the two compounds 8CB and 9CB, which show a AN transition, it was found that, within the resolution of the experiments, these transitions are second-order. The anomalous heat capacity observed near the AN transition is much larger for 9CB than for 8CB. The critical exponent α obtained from power law fits to the heat capacity data is 0.31 ± 0.03 for 8CB and 0.50 ± 0.05 for 9CB. It is suggested that the AN transition in 9CB must be...

70 citations

Journal ArticleDOI
S. Torza1, P. E. Cladis1
TL;DR: In this paper, the authors measured a change in specific volume of (0.5 \ifmmode\times\else\texttimes\fi{} ${10}^{\ensuremath{-}4}$ ${\math{cm}}^{3}$/g at the nematic-smectic-$A$ transition of
Abstract: We have measured a change in specific volume of (0.5 \ifmmode\pm\else\textpm\fi{} 0.2) \ifmmode\times\else\texttimes\fi{} ${10}^{\ensuremath{-}4}$ ${\mathrm{cm}}^{3}$/g at the nematic-smectic-$A$ transition of $\mathrm{N}\ensuremath{-}p\ensuremath{-}\mathrm{cyanobenzylidene}\ensuremath{-}p\ensuremath{-}\mathrm{octyloxyaniline}$. The order of this transition has recently been subject to dispute. On the basis of our data, we conclude unambiguously that it is of first order as is expected from theoretical analysis.

70 citations