Corrélations entre les Anisotropies Optique et Magnétique de Phases Uniaxes dans une Série Homologue de Cristaux Liquides: Application à la détermination optique des variations thermiques du paramètre d'ordre
“…The interference of the nematic-smectic A phase transition following this narrow range may explain the high value of thermal expansion coefficient in the nematic phase. Gasparoux, Lalanue and Martin (1979) reported a significant change in optical birefringence in the nematic phase of HYBBA and our results qualitatively agree with their observations. It is apparent from the variation of thermal expansion coefficient with temperature (Figure 3) that pretransitional effects are found to occur on both sides of the nematic-isotropic transition and the characteristic constants A from Maier-Saupe's table (1960), are found to be 0.4405 and 29.9 x m8 kg s -~ respectively.…”
Section: Resultssupporting
confidence: 95%
“…Hence it is apparent from the slopes that the change in degree of order in the smectic-A phase is smaller than in the nematic phase. Gasparoux, Lalanue and Martin (1979) carried out optical birefringence and susceptibility studies on HYBBA and they found abrupt jumps at the nematic to smectic-A transition suggesting it was of first order. The reported transition energy values for this compound and other weakly polar and polar compounds are presented in Table 11.…”
The density p of N(p-ti-heptyloxy benzylidene) p-n-butyl aniline (HYBBA) is measured as a function oftemperature from the isotropic liquid to the smectic-G phase. The compound is tetramorphic exhibiting three smectic phases s,, s,-, s,., and a nematic phase. The density changes across the phase transformations and the calculated thermal expansion coefficient confirm the order of the S,-Sc, S,-Nand N-Itransitions as first-order, with Sc-S, transition as weakly first or second-order. The first-order S,-N phase transformation in this compound, which is weakly polar, is in agreement with McMillan's theoretical predictions, and is different from other polar compounds.
“…The interference of the nematic-smectic A phase transition following this narrow range may explain the high value of thermal expansion coefficient in the nematic phase. Gasparoux, Lalanue and Martin (1979) reported a significant change in optical birefringence in the nematic phase of HYBBA and our results qualitatively agree with their observations. It is apparent from the variation of thermal expansion coefficient with temperature (Figure 3) that pretransitional effects are found to occur on both sides of the nematic-isotropic transition and the characteristic constants A from Maier-Saupe's table (1960), are found to be 0.4405 and 29.9 x m8 kg s -~ respectively.…”
Section: Resultssupporting
confidence: 95%
“…Hence it is apparent from the slopes that the change in degree of order in the smectic-A phase is smaller than in the nematic phase. Gasparoux, Lalanue and Martin (1979) carried out optical birefringence and susceptibility studies on HYBBA and they found abrupt jumps at the nematic to smectic-A transition suggesting it was of first order. The reported transition energy values for this compound and other weakly polar and polar compounds are presented in Table 11.…”
The density p of N(p-ti-heptyloxy benzylidene) p-n-butyl aniline (HYBBA) is measured as a function oftemperature from the isotropic liquid to the smectic-G phase. The compound is tetramorphic exhibiting three smectic phases s,, s,-, s,., and a nematic phase. The density changes across the phase transformations and the calculated thermal expansion coefficient confirm the order of the S,-Sc, S,-Nand N-Itransitions as first-order, with Sc-S, transition as weakly first or second-order. The first-order S,-N phase transformation in this compound, which is weakly polar, is in agreement with McMillan's theoretical predictions, and is different from other polar compounds.
“…The thermal expansion coefficient and an anomalous dip in the ultrasonic velocity (Rao and Pisipati, unpublished) suggest a first-order phase transition. Our results are in good agreement with the reported data observed by refractive index measurements (Gasparoux, Lalanue and Martin, 1979;O'Shea and Kuster, 1981).…”
“…The data for the aromatic rings and for the aliphatic carbons are presented in Figures and . They are fitted to the Haller equation: − where S 0 and F are empirical constants and T * is a temperature at which the order parameter becomes zero. 4 Plot of order parameters of the aromatic rings of 4‘-cyanobiphenyl hexanoate against T / T *, with T * = 343.6 K. The open squares are for the nonprimed ring; the filled circles are for the primed ring.…”
A new approach is presented for the determination of long-range dipolar couplings in liquid crystals. The
strategy is the use of monodeuterated compounds to observe 2H−13C splittings in the 13C NMR spectra. As
examples, the H−C dipolar coupling constants have been obtained from the spectra of 4‘-cyanobiphenyl
2-deutero- and 6-deuterohexanoate over the whole nematic range. In addition, the 2H NMR spectra of these
compounds taken with 1H−H dipolar decoupling show quadrupolar splitting and 1H−H dipolar coupling.
Besides the information obtained from the 1D spectra, one-bond and two-bond 1H−13C dipolar coupling
constants of 4‘-cyanobiphenyl hexanoate were determined using the method of proton encoded local field
(PELF) spectroscopy in combination with off-magic-angle spinning (OMAS). The order parameters were
calculated from the 2D spectra, and some of the coupling constants are compared with the H−C coupling
constants obtained from the 1D experiments.
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