DSC studies on p-(n-alkyl)-p′-cyanobiphenyl (RCB’s) and p-(n-alkoxy)-p′-cyanobiphenyl (ROCB’s) liquid crystals

Oweimreen, G. A.; Morsy, Mohamed A.

doi:10.1016/s0040-6031(99)00411-6

Cited by 89 publications

(80 citation statements)

References 16 publications

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“…The peak temperatures extracted from the DSC spectra are in good agreement with those reported in the literature for similar experiments [10,14]. Since the entropy jump is related to the latent heat, i.e., ΔH=T ΔS, where T is the transition temperature and ΔS is the entropic change, the calorimetric measurements determine the order of each phase transition.…”

Section: Uv Spectroscopysupporting

confidence: 87%

“…The spectra were recorded at room temperature in a 1-cm quartz cuvette. The samples were separately placed in the [10]. The good agreement between the values in the literature [10][11][12][13] and the sharp transition temperatures in our measurements attests to the high purity of our LCs.…”

Section: Uv Spectroscopysupporting

confidence: 82%

“…Important characteristics, such as the melting and clearing temperatures and their enthalpies [9], can be computed from a single data run. Measurements for 8CB and 8OCB and other members of the homologous series were carried out by Oweimreen et al [10] using an adiabatic scanning calorimeter, and the electro-optical properties of these liquid crystals were reported by BDH Chemicals [11]. Information on the phase-transition temperature and transition enthalpy of a pure liquid crystal allows one to estimate the effect of the mixture ratio (in wt.…”

Section: Introductionmentioning

confidence: 99%

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Thermal and Spectrophotometric Analysis of Liquid Crystal 8CB/8OCB Mixtures

Özğan

Okumuş

2011

Braz J Phys

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The binary system of 4-octyl-4′-cyanobiphenyl (8CB) and 4-octyloxy-4′-cyanobiphenyl (8OCB) has been studied by means of differential scanning calorimetry (DSC) and ultraviolet absorption spectrophotometry (UV). The phase-transition temperatures, enthalpies, and entropies have been determined by using calorimetric methods on DSC. The results indicate clearly the existence of threephase regions across the crystalline-to-smectic A, smectic A-to-nematic, and nematic-to-isotropic transitions in the 8CB/8OCB mixtures. The obtained phase-transition temperatures of the 8CB/8OCB mixtures are between the data for 8CB and 8OCB. A few of the phase transitions cannot be observed at high heating rates. The phase-transition temperatures of the 8CB/8OCB mixtures rise with the heating rate between 2°C/min and 15°C/min. The activation energies were calculated by the Ozawa method for the phase transitions of 25% 8CB and 75% 8OCB liquid crystal mixtures. UV experiments were carried out to characterize the absorptivity constants of liquid crystal and their mixtures. The molar absorptivity and maximum absorption wavelengths were measured in chloroform solution by UV spectrophotometry. The maximum absorption wavelength of the 8CB/8OCB mixtures increases with decreasing percent weight of 8CB in 8OCB, a result associated with the different lengths of the alkyl chain.

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Section: Uv Spectroscopysupporting

confidence: 87%

Section: Uv Spectroscopysupporting

confidence: 82%

Section: Introductionmentioning

confidence: 99%

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Thermal and Spectrophotometric Analysis of Liquid Crystal 8CB/8OCB Mixtures

Özğan

Okumuş

2011

Braz J Phys

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“…Additionally, a correction factor Θ = 0.96 was used to normalize the slight difference between the latent heat value predicted by the phenomenological model parameters used (term 3 of eqn. 18) to an experimentally determined approximate reference value of ∆Hexp = 4.85kJ/mol [63]. The latent heat predicted by the model and phenomenological parameters (determined previously [62]) is:…”

Section: Simulation Conditionsmentioning

confidence: 96%

Nonisothermal Model for the Direct Isotropic/Smectic-A Liquid-Crystalline Transition

Abukhdeir

Rey

2009

Langmuir

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An extension to a high-order model for the direct isotropic/smectic-A liquid crystalline phase transition was derived to take into account thermal effects including anisotropic thermal diffusion and latent heat of phase-ordering. Multi-scale multi-transport simulations of the nonisothermal model were compared to isothermal simulation, showing that the presented model extension corrects the standard Landau-de Gennes prediction from constant growth to diffusion-limited growth, under shallow quench/undercooling conditions. Non-isothermal simulations, where meta-stable nematic pre-ordering precedes smectic-A growth, were also conducted and novel non-monotonic phase-transformation kinetics observed.

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“…Thus, for the abovementioned phase transitions thermal hysteresis takes place. Availability of thermal hysteresis and T* and T** temperatures at the phase transitions in liquid crystals was theoretically predicted in [11,14,38,[40][41][42][43][44][45][46] and was experimentally observed in [47][48][49][50][51][52][53][54][55][56].…”

Section: Resultsmentioning

confidence: 99%

Liquid crystalline material exhibiting multiple phase transitions: morphologic properties and optical transmission

Nesrullajev¹

2017

Lith. J. Phys.

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Morphologic and thermo-optical properties of liquid crystalline material exhibiting multiple phase transitions were investigated in this work. Investigations were carried out for both the direct (by heating) and the reverse (by cooling) phase transitions. Thermo-morphologic properties of the heterophase regions of phase transitions were investigated. Temperature dependences of the optical transmission were studied, the mean optical density of crystalline state, smectic C, smectic A and nematic mesophases was estimated, temperature widths of the heterophase regions of crystal ↔ smectic C, smectic C ↔ smectic A, smectic A ↔ nematic and nematic ↔ isotropic liquid phase transitions were determined with high accuracy.

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DSC studies on p-(n-alkyl)-p′-cyanobiphenyl (RCB’s) and p-(n-alkoxy)-p′-cyanobiphenyl (ROCB’s) liquid crystals

Cited by 89 publications

References 16 publications

Thermal and Spectrophotometric Analysis of Liquid Crystal 8CB/8OCB Mixtures

Thermal and Spectrophotometric Analysis of Liquid Crystal 8CB/8OCB Mixtures

Nonisothermal Model for the Direct Isotropic/Smectic-A Liquid-Crystalline Transition

Liquid crystalline material exhibiting multiple phase transitions: morphologic properties and optical transmission

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