P. Pardhasaradhi

Histogram equalisation technique to analyse induced cholesteric phase in nanodoped liquid crystalline compound

The 1% Fe3O4 nanodoped in dodecyloxy benzoic acid induces cholesteric phase quenching the nematic phase that the pure compound exhibits. Further, the solid–solid transition also occurs when compared to the pure compound and the transition temperatures are reduced along with the cholesteric thermal ranges of LC phases. The histogram is the operation by which the occurrences of intensity value in the image is shown. Further, histogram equalisation is the technique through which the dynamic range of the histogram of an image can be increased. Histogram equalisation method is used in this article to analyse the 12Oba + 1% Fe3O4 nanodoped liquid crystalline textures by considering global and local image information and for the adjustment of image intensities to enhance the contrast. The basic idea of histogram equalisation is to remap the grey levels of the image, and this method is used to identify the uniform regions and detect the defects that are not clearly observed from the textures that are recorded by polarising microscope.

Image enhancement using virtual contrast image fusion on Fe3O4 and ZnO nanodispersed decyloxy benzoic acid

Low contrast and noisy photographic pictures can be considerably improved by image-processing techniques. Techniques like histogram equalisation produce high-contrast images but often fail to preserve the colour texture information. To overcome this deficiency, a contrast-enhancement approach has been devised, using virtual contrast image fusion (in Haar wavelet domain). This technique has been evaluated by a study of the optical textures of nano-dispersed decyloxybenzoic acid with small quantities of Fe3O4 and ZnO added.

Homomorphic filtering textural analysis technique to reduce multiplicative noise in the 11Oba nano-doped liquid crystalline compounds

The compound undecyloxy benzoic acid (11Oba) exhibits nematic and smectic-C phases while a nano-doped undecyloxy benzoic acid with ZnO exhibits the same nematic and smectic-C phases with reduced clearing temperature as expected. The doping is done with 0.5% and 1% ZnO molecules. The clearing temperatures are reduced by approximately 4 ° and 6 °, respectively (differential scanning calorimeter data). While collecting the images from a polarizing microscope connected with hot stage and camera, the illumination and reflectance combined multiplicatively and the image quality was reduced to identify the exact phase in the compound. A novel technique of homomorphic filtering is used in this manuscript through which multiplicative noise components of the image are separated linearly in the frequency domain. This technique provides a frequency domain procedure to improve the appearance of an image by gray level range compression and contrast enhancement.

Gradient measurement technique to identify phase transitions in nano-dispersed liquid crystalline compounds

Characterization and phase transitions in pure and 0.5% BaTiO3 nano-dispersed liquid crystalline (LC) N-(p-n-heptyloxybenzylidene)-p-n-nonyloxy aniline, 7O.O9, com-pounds are carried out using a polarizing microscope attached with hot stage and camera. We observed that when any of these images are distorted, different local structures suffer from various degradations in a gradient magnitude. So, we examined the pixel-wise gradient magnitude similarity between the reference and distorted images combined with a novel pooling strategy – the standard deviation of the GMS map – to determine the overall phase transition variations. In this regard, MATLAB software is used for gradient measurement technique to identify the phase transitions and transition temperature of the pure and nano-dispersed LC compounds. The image analysis of this method proposed is in good agreement with the standard methods like polarizing microscope (POM) and differential scanning calorimeter (DSC). 0.5% BaTiO3 nano-dispersed 7O.O9 compound induces cholesteric phase quenching the nematic phase, which the pure compound exhibits.

Orientational order parameter studies on 3.Om and 3O.Om liquid crystals

Orientational order parameter S is evaluated in the nematic phase of six liquid crystal compounds, N-(p-n-propyl benzylidene)-p-n-alkoxy anilines, 3.Om and N-(p-n-propyloxy benzylidene)-p-n-alkoxy anilines, 3O.Om compounds with m = 6, 7 and 8, using different methods. The techniques employed are S from birefringence δn, Hallers approximation from (1−T/Tc) β, effective geometry parameter αg and Vuks’ scaling factor SC. The values of S obtained using the above methods are compared with one another and with the results on a number of liquid crystals; the liquid crystals favor isotropic Vuks’ method.

Phase Transitions and Order Parameter Studies from Polarizabilities in 3.Om and 3O.Om Liquid Crystalline Compounds

As a part of our systematic studies on liquid crystals of nO.m, n.Om, nO.Om and n.m homologous series, n-(p-n-alkoxy/alkylbenzylidene)-p-n-alkyl/alkoxy anilines, we present in this article the nature of phase transitions across isotropic–nematic exhibited by all the compounds mentioned below. Further, the orientational order parameter in the nematic phase of N-(p-n-propyl/propyloxy benzylidene)-p-n-alkoxy anilines, 3.Om and 3O.Om with m = 6–8 are estimated from the molecular polarizabilities calculated using the experimental refractive indices and density results. The molecular polarizabilities αe and αo are obtained for all the compounds using the above results for both Vuks and Neugebauer local field models applicable to nematic liquid crystal. αe and αo calculated in this way are used to obtain Δα. The polarizability anisotropy in the perfect order (absolute K) is calculated theoretically using the δ-function model developed by Lippincott et al. and molecular vibration method. These enabled the calculation of the orientational order parameter S. The values of polarizability anisotropy for both local electric field models differ significantly. No criterion is known to decide which value is correct. To avoid the determination of uncertain α and Δα values considering different local field models, a simple procedure developed by Kuczynski et al. was used for evaluation of S, based solely on birefringence measurement and this value of S is compared with those obtained from field models.

Estimation of order parameter from different models in symmetric dimeric liquid crystals

The birefringence measurements with the temperature are carried out employing the wedge technique at the wavelength λ = 5893Å on symmetric dimeric liquid crystalline compounds of α,ω-bis(4-alkylanilinebenzylidene-4′-oxy) alkanes which are popularly known as m.OnO.m’s with m = 3, 4 and 5 and spacer length n = 8, 9 and 10. The studied compounds are mono variant with long range of nematic phase. The birefringence data δn = (ne–no) along with the density results are employed to estimate the molecular polarisabilty anisotropy, δα = (αe–αo) assuming a particular local field (due to Vuks and Neugebauer) the nematic molecule experiences and the order parameter S is estimated from δα and Δα, i.e., polarisabilty anisotropy which is estimated employing different methods. Further, S can also be obtained from Kuczynski model and also using the effective geometry parameter, αg. Further, it is observed that from our analysis the S value obtained from Δn and αg are identical. The results are analysed and compared with the data available in the literature.

Image enhancement of nano-dispersed N-(p-n-decyloxybenzylidene)-p-n-hexyloxy aniline using combined unsharp masking

ABSTRACT The main objective of the image enhancement is to process an image with suitable technique to produce better visibility for a specific application. To identify key features like transition temperatures, clear phase identification in the liquid crystalline images, we require some novel image processing techniques. Characterisation and mesomorphic behaviour in pure and 1% ZnO nano-dispersed liquid crystalline N-(p-n-decyloxybenzylidene)-p-n-hexyloxy anilines, 10O.O6 compounds are carried out using a polarising microscope and images are preserved for enhancement. Both the compounds exhibits NACIG (nematic, smectic-A, smectic-C, smectic-I, smectic-G) phases and the transition temperatures of the 1% ZnO nano-dispersed 10O.O6 are reduced compared with pure 10O.O6. Further, in this paper, a novel image enhancement technique of combined unsharp masking is proposed on pure and 1% ZnO nano-dispersed 10O.O6 liquid crystalline compounds for better visibility of phases at transition temperatures. The proposed method is used to identify the uniform regions and to detect the defects which may not be clearly observed from the textures that are recorded by polarising microscope.

Dispersive power and crossover temperature, TCO, of two polar nematic liquid crystals in the visible spectral region

Refractive index studies are carried out on two highly polar liquid crystals: 1. N-(p-n-methoxy benzylidene)-p-amino benzonitrile, PmBAB, 2. N-(p-n-ethoxy benzylidene)-p-amino benzonitrile, PeBAB. The experimental investigations are carried out in the visible region at four different wavelengths, namely, 633, 589, 546 and 436 nm. The two compounds exhibit only the nematic liquid crystalline phase in between the isotropic and crystalline solid. The dispersive power ω is estimated for two consecutive wavelengths for the case of , ne and no for different wavelengths and found to be constant with temperature. Further the temperature gradients of ne and no are estimated, and the crossover temperature is obtained using dno/dT for all the wavelengths.

Synthesis, characterization and phase transition studies in 4-hexyloxy benzylidene 4’-alkoxyanilines

ABSTRACT Synthesis and the characterization through polarizing optical microscope (POM) textures in number of 4-hexyloxy benzylidene 4’-alkoxyanilines, 6O.Om with m = 4, 6 to 10 liquid crystalline materials are carried out. Furthermore, the density and thermal expansion coefficient results reveal that the phase transitions present, viz., isotropic–nematic, nematic–SmC and SmC–SmI show first-order nature as expected. The transition temperatures obtained thorough the differential scanning calorimetry is found to be in agreement with the literature data. The first two compounds exhibit only the nematic phase while the next four compounds show enantiotropic SmC phase as per the literature data. The compound with m = 10 exhibits monotropic SmI phase. However, we, the authors, are able to observe this phase in addition to SmC and nematic through POM only as per the literature. The parameters calculated across the phase transitions and in the phases are in agreement with the body of the data available.