Temperature Behavior of the Electric Field-Induced Entropy Increment within a Homologous Series of Nematogenic Compounds

Jadżyn, Jan; Sokołowska, Urszula; Déjardin, Jean‐Louis

doi:10.1021/jp802923b

Cited by 23 publications

(27 citation statements)

References 16 publications

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“…As was shown recently, the S (T ) dependence reflects molecular self-association such as, for example, dipolar coupling in isotropic mesogenic liquids in the vicinity of the transition to the nematic phase [37][38][39][40] or hydrogen bond formation in liquid amides [30]. The negative values of S (Fig.…”

Section: Figmentioning

confidence: 54%

Temperature Behavior of Electric Relaxational Effects due to Ionic Conductivity in Liquid Lactones

Świergiel

Jadżyn

2012

Int J Thermophys

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This paper concerns the studies of temperature and frequency behavior of the complex impedance, electric modulus, and electric conductivity due to an ionic current in liquid γ -butyrolactone (GBL) and γ -valerolactone (GVL). The frequency of the applied electric stimulus (500 Hz to 5 MHz) corresponds to the static dielectric regime of the lactones. The studies were performed in the temperature range of 263 K to 313 K. It was shown that in the static dielectric case, the dc ionic conductivity (σ DC ) and the static dielectric permittivity (ε s ) determine the relaxational behavior of the impedance (Z * ) and the electric modulus (M * ) of the molecular liquids and both spectra are of the Debye-type characterized by the same conductivity relaxation time (τ σ ). Both σ DC and τ σ of GBL and GVL fairly well fulfill an Arrhenius temperature dependence with very similar values of the thermal activation energy E σ DC ≈ E τ σ ≈ 25 kJ · mol −1 . The temperature dependence of the static dielectric permittivity and its temperature derivative is analyzed and interpreted in terms of the dipolar aggregation in the studied lactones.

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Section: Figmentioning

confidence: 54%

Temperature Behavior of Electric Relaxational Effects due to Ionic Conductivity in Liquid Lactones

Świergiel

Jadżyn

2012

Int J Thermophys

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“…The pretransitional anomalies in ε s are possible only for compounds with permanent dipole moment but some other conditions enabling the molecular associations could be discussed simultaneously. As it was suggested earlier [7], the magnitude of the pretransitional effect in ε s can be characterized by the difference between the temperature corresponding to the permittivity maximum and the clearing temperature, δT = T max −T c . This definition is somewhat confusing in the case when a curvature but no maximum is observed in ε s .…”

Section: Dielectric Pretransitional Effectmentioning

confidence: 90%

“…As a result, the angle between the vector of the dipole moment and the long axis of this molecule is about 12 • . [7]. c From [21].…”

Section: Dielectric Relaxationmentioning

confidence: 98%

“…Bradshaw and Raynes assumed that above the nematic-isotropic (N-I) phase transition there are some domains with nematic-like order (prenematic domains) [5]. Some authors suggested that the magnitude of the pretransitional dielectric permittivity anomaly is correlated with the N-I phase transition type (typical first-order or weakly first-order) [6,7]. However, the results of calorimetric investigations of the transition enthalpy did not confirm this assumption [8].…”

Section: Introductionmentioning

confidence: 99%

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Prenematic Self-Assembling of Mesogenic Molecules in Isotropic Liquid and Orientational Order in Nematic Phase

et al. 2011

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Dielectric relaxation study of nematogenic 4-n-alkyl-4 -cyanobiphenyls (nCB, n = 5, 6), 4-(trans-4 -n-alkylcyclohexyl)isothiocyanatobenzenes (nCHBT, n = 6, 8), 4-cyanophenyl-4 -n-alkylbenzoates (nCPB, n = 6, 8), 4-cyano-3-fluorophenyl-4 -n-octyloxybenzoate (8OCFPB), and 4-cyanophenyl-4 -n-octyloxy-3 -fluorobenzoate (8OCPFB) was performed in the frequency range from 50 kHz to 100 MHz in the nematic and isotropic phases. The static permittivity and the relaxation process related to the rotation of molecules around their short axis was analyzed. For some of these liquid crystals anomalous temperature dependence of static permittivity in the pretransitional region of the isotropic phase was observed. Based on the Meier-Saupe-Martin model of molecular diffusion in nematics, the orientational order parameter P 2 was determined from dielectric relaxation times and retardation factor. The values of P 2 calculated from the dielectric relaxation data were compared with the results obtained from measurements of polarized electronic absorption. Correlations between the magnitude of the dielectric pretransitional effect and the orientational order in the nematic phase were discussed.

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“…Recently, the dielectric properties of nematogenic com− pounds belonging to the homologous series of 4−cyanophe− nyl−4'−n−alkylbenzoates (C n H 2n+1 PhCOOPhCN, n = 4-10) had been investigated in the isotropic phase [5] and detailed dielectric study for 4−cyanophenyl−4'−n−heptylbenzoate (7CPB) in both the nematic and isotropic phases had been carried out [6]. The ability of the molecules to the self−orga− nization in the vicinity of the isotropic−nematic (I−N) transi− tion had been found.…”

Section: Introductionmentioning

confidence: 99%

Dielectric and orientational properties of nematogenic 4-n-octyl(4′-cyanophenyl)benzoate

Bauman

Jadżyn

Wolarz

et al. 2010

Opto-Electronics Review

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Experimental studies of the dielectric properties in the nematic and isotropic phases of 4-cyanophenyl-4′-n-octylbenzoate (8CPB) have been performed in the frequency range from 50 kHz to 100 MHz. The relaxation process related to the rotation around the short molecular axis has been analysed. The results obtained have revealed that in the vicinity of the I-N phase transition, the molecular subdiffusional rotation process occurs. It is connected with the pretransitional effects which are observed both in the static and dynamic dielectric measurements. On the basis of the temperature dependence of the relaxation time in the nematic and isotropic phases, the orientational order parameter 〈P2〉 has been determined. The values of 〈P2〉 obtained in this way have been compared with those evaluated from the measurements of the polarized electronic absorption of the dichroic dye, dissolved as guest probe in the mesogenic host.

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Temperature Behavior of the Electric Field-Induced Entropy Increment within a Homologous Series of Nematogenic Compounds

Cited by 23 publications

References 16 publications

Temperature Behavior of Electric Relaxational Effects due to Ionic Conductivity in Liquid Lactones

Temperature Behavior of Electric Relaxational Effects due to Ionic Conductivity in Liquid Lactones

Prenematic Self-Assembling of Mesogenic Molecules in Isotropic Liquid and Orientational Order in Nematic Phase

Dielectric and orientational properties of nematogenic 4-n-octyl(4′-cyanophenyl)benzoate

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