IJERT-Thermo-Optical and Order Parameter Studies by Image Analysis (original) (raw)
Related papers
Calculation of Optical Parameters of Liquid Crystals
Acta Physica Polonica A
Validation of a modified four-parameter model describing temperature effect on liquid crystal refractive indices is being reported in the present article. This model is based upon the Vuks equation. Experimental data of ordinary and extraordinary refractive indices for two liquid crystal samples MLC-9200-000 and MLC-6608 are used to validate the above-mentioned theoretical model. Using these experimental data, birefringence, order parameter, normalized polarizabilities, and the temperature gradient of refractive indices are determined. Two methods: directly using birefringence measurements and using Haller's extrapolation procedure are adopted for the determination of order parameter. Both approches of order parameter calculation are compared. The temperature dependences of all these parameters are discussed. A close agreement between theory and experiment is obtained.
PHASE TRANSITION AND OPTICAL ANISOTROPY OF TERNARY MIXTURE OF LIQUID CRYSTALS WITH TEMPERATURE
Trans Stellar Journals, 2021
The goal of this study is to look at how texture changes as a function of temperature in a mixture of liquid crystalline materials. The effects of temperature on optical anisotropy measurements have also been studied. The organic liquid crystal compound 4-(2-methylbytyl) phenyl 4-(4-octylphenyl) benzoate(CE8) is a ferroelectric liquid crystal composed of rod-like molecules that exhibits a chiral smectric phase with stable Blue phase, Diethyl 4,4lAzoxydicinnamate exhibits a cholesteric liquid crystalline phase, and Cholesteryl nonanoate exhibits a choleste When a mixture of 4-(2-methylbytyl) phenyl 4-(4-octylphenyl) benzoate(CE8),Diethyl4,4lAzoxydicinnamate, and Cholesteryl nonanoate molecules in equal proportions is cooled from its isotropic phase, it shows cholesteric, SmA, and SmE successively. This is found to exhibits for all different concentrations of given mixture. The phase transition have been characterised using polarising microscopic technique. The temperature variations of optical anisotropic measurements shows that the refractive indices of liquid crystalline ternary mixture shows almost non linear increase in extraordinary refractive index while non linear decrease and then increase in ordinary refractive index, when specimen is cooled from its isotropic phase. The temperature variations of optical anisotropic measurements have noted using Goniometer spectrometer.
Optical Measurements of Thermotropic Liquid Crystals
Journal of Modern Physics, 2013
In this work, an experimental approach was used for measuring birefringence of thermotropic liquid crystal materials at different wavelengths in the visible region by using speckle interferometry. Also the values of the refractive indices were measured for these thermotropic liquid crystal materials in isotropic and liquid crystal phases at different wavelengths. Temperature dependency of the refractive indices for each LC sample at certain wavelengths was investigated in the isotropic and in LC phases.
Journal of Molecular Liquids, 2016
Study of optical texture of different mesophases and phase transition temperatures of the liquid crystal compound 4,4′-din -heptyloxy-azoxy benzene has been carried out by using optical polarizing microscope. Enthalpy values and the phase transition temperatures have also been conducted by DSC studies. The variation of refractive indices with temperature has been measured by a thin prism technique using He-Ne laser and temperature dependent birefringence is calculated which shows a moderate value. Validation of the modified four-parameter model based on Vuks approximation has been carried out and reported in this article. The most important characteristics of LC compound namely macroscopic and microscopic order parameter have been evaluated by using direct extrapolation method and modified Vuks method based on Haller's extrapolation respectively. Temperature gradients of refractive indices have also been calculated. Further the normalized polarizabilities for extraordinary and ordinary rays and their ratio have been reported in this paper.
Acta Physica Polonica A, 2012
The variation of refractive indices with temperature of three pure nematogenic compounds 5OCB, CPHB and 6CHBT were studied experimentally using thin prism technique. The refractive indices no and ne were measured using 633 nm lines from a HeNe laser. A modied four-parameter model was taken which is based on the Vuks equation describing the eect of temperature on the refractive indices of liquid crystals. In this paper we report the variation of refractive indices of these three liquid crystals with temperature, using the thin prism method. The variation in birefringence was determined experimentally. The variation in refractive indices and birefringence were also tted theoretically using the modied Vuks equation. On comparison, the theoretically tted values show close agreement with the experimental values.
Journal of Photonic Materials and Technology, 2020
Study the optical-thermal dependence of liquid crystal based on the quantity data of image texture is important to get more information accurately. In this research, the optical-thermal dependence of chiral nematic liquid crystals ink sample was investigated based on the texture and color changes of the sample at various temperatures. The textures of the samples were recorded by the crossed-polarizing optical microscope attached to the hot stage and a camera. The temperature dependence of textures are represented by the hue parameter values taken from the HSV image type. The result obtained from the graph of the increase mean hue parameter against the temperatures was in accordance with the preceding results done by the various techniques. The results show that the higher the temperature of the material, the higher the average hue value. The increase in the hue parameter relates to the color changes of texture from red-dominant to green-dominant. The color difference appeared in various wavelengths represent a diffraction pattern caused by its optically active and the twisted molecular structure. Approaching to the Bragg diffraction equation, the pitch obtained at 0.7 µm. Furthermore, the relation of the different textures and the twist structure of the sample was evaluated. Considering the sample thickness of 100 µm carries out to the conclusion that there are hundreds of twisted nematic liquid crystal molecules in various alignment on a volume space.
Trans Stellar Journals, 2021
The goal of this research is to look at how texture changes as a function of temperature in a mixture of liquid crystalline materials. Also the temperature variations of refractive indices of sample is studied. Theorganic compoundDiethyl4-4lHexaloxy Azoxy Benzoate exhibits Smectic liquid crystalline phase and the compound cholesterylnonanoateis cholesteric liquid crystal. Mixture of 70% Diethyl 4-4lHexaloxy Azoxy Benzoate and 30% of cholesterylnonanoatemolecules exhibits cholesteric, SmA and SmE sequentially when specimen is cooled from its isotropic phase. This is observed at all concentrations of a given combination. The microscopic approach was used to characterise these phases. A Gonio metre spectrometer was used to measure temperature fluctuations in optical anisotropy tests. The temperature changes of liquid crystalline binary mixture refractive indices indicate an almost non linear drop in extraordinary refractive indices with increasing temperature, but a non linear decline and subsequent increase in ordinary refractive indices.
Temperature effect on refractive indices and order parameter for mixture liquid crystal (UCF)
2015
Liquid crystals are state of substance possesses characteristics between traditional liquid and crystallization. For instance, perhaps liquid crystal away similar to the crystals. There are different types of crystal in the liquid phase .In this research has been the use of high refractive birefringence as well as (UCF), the study of the influence of temperature on the refractive indices at wavelength (623.8 nm), and room temperature. In addition, we used the fourparameters model to study this case, and compared between the experimental results with theoretical. This study is showed, when the temperature increases the ordinary refractive indices (no) increases. And both the extraordinary refractive indices (ne), optical anisotropy (birefringence Δ n) are decreases, also we find the order parameter (S) decreased as the temperature is increased.
Journal of Molecular Liquids, 2020
Temperature dependent optical properties like birefringence, temperature gradients of refractive indices, molecular polarizabilities, effective geometry parameter, order parameter and cross over temperatures have been investigated for nine different liquid crystal mixtures. These mixtures are prepared by mixing two pure nematic liquid crystal compounds, namely, 4-n-pentyl phenyl 4-n′-hexyloxybenzoate (ME6O.5) and 4-cyanophenyl 4′n-pentyl benzoate (CPPB) where, ME6O.5 is a monotropic compound and CPPB is an enantiotropic compound. The mixtures however are found to be exhibit induced smectic phases. The theoretical fitting values obtained by using Hallers' extrapolated method of birefringence values agree quite well with the experimental values. It is observed that the normalized polarizability behaves exactly as refractive indices when it is plotted against temperature. The effective geometry parameter (α eg) of the mixture having highest birefringence shows highest value of α eg at certain temperature. Finally, order parameters of the mixtures have been calculated using five different techniques and for all mixtures the order parameters shows characteristics range from 0.3-0.9. The abrupt changes in order parameter before nematic phases are due to the existence of the induced smectic phases in the liquid crystal mixtures.
Advanced Materials Proceedings
In this article, our intention is to observe the mesophase textures of a liquid crystal (LC) compound 4nonyloxybenzoic Acid (9OBA) in an attempt to understand the nature of dramatic changes of the mesophase transition textures with temperature. The studies of mesophase textures were carried out by using polarizing optical microscope (POM). Mesophase transition temperatures and their corresponding enthalpy changes (during heating) are experimentally deduced from differential scanning calorimetry (DSC). Higher value of enthalpy changes has been observed for the solid crystalline to Smectic C (SmC) transition. The compound 9OBA is found to exhibit nematic and SmC mesosphase and may be useful for the projection display since it exhibits high clearing temperature.