Debanjan Bhattacharjee

Negative Birefringence in the Higher Homologs of the 5O.m Series of Liquid Crystals

A detailed study of the different parameters of the higher homologs of the 5O.m (m = 14, 16) series of liquid-crystalline compounds is reported. These are interdigitated compounds with unsymmetrical alkyl chain length. The compounds have a unique nature, unlike the other members of the nO.m series. The molecular structure reported in this article is not purely uniaxial; it has a bending tendency. In this article, we report that both the compounds exhibit negative birefringence. For the optical study, the refractive indices, ne and no, of the sample are measured by the thin-prism technique, using a He-Ne laser beam of wavelength 633 nm. A four-parameter model was used for fitting the experimental results. From the experimentally measured refractive indices, it is possible to compare different parameters with those of the theoretical models.

Correlation between the density and refractive index with higher homologues 5O.m series

ABSTRACT The density dependent refractive indices study of the higher homologues liquid crystalline compound 5O. m (m = 14, 16) is reported in this paper. The compounds are interdigitated with highly skewed alkyl chains. The density study of the sample has been done with the capillary tube method. For the refractive indices study, the extraordinary component ne and the ordinary component no of the samples were measured by the thin prism technique with He-Ne laser beam of wavelength 633 nm. These the results obtained were used to find the correlation between the density and refractive indices in both samples.

Density and phase transition study of the liquid crystal compound 50.16

Density and phase transition study for a liquid crystalline compound (50.16) is reported in this paper. This liquid crystalline compound as it is highly skewed in alkyl chain length. We experimentally measured the phase transition temperatures for the compound using a polarizing optical microscopy and differential scanning calorimeter. The densities of this liquid crystalline compound across all its phases as a function of temperature were measured using a capillary type dilatometer. The densities of the liquid crystals were calculated by correcting for the expansion of the glass capillary tube. These methods were found to be highly suitable for the calculation the phase transition and density of liquid crystalline with respect to temperature. The density data was used to calculate several parameters that provide an understanding of the phase behavior in such skewed liquid crystalline compounds.

Comparative experimental optical studies on 7.O5O.7 dimeric liquid crystal compound using theoretical models

ABSTRACT In the present study, the optical properties of the 7.O5O.7 dimeric compound are reported. This dimeric compound exhibits typical smectic A to smectic F phase transition, and the main focus of our study is to observe the optical behaviour in SmA phase. In the dimeric compound, the two mesogens are connected by a linkage group or spacer. The presence of the linkage group and the terminal alkyl chains plays a vital role to change the behaviour of this compound as compared to the traditional monomeric compounds. Study of birefringence, refractive indices and normalised polarisation are essential to investigate the optical nature in liquid crystalline compounds. The optical study in our compound is carried out by using the thin prism experimental method with the help of He-Ne laser of wavelength 633 nm. Four-parameter model was used to obtained theoretically measured refractive indices and birefringence data. The theoretical results are then compared with the experimental results. Both the experimentally and theoretically calculated results are properly fitted in our dimeric compound. Graphical Abstract

Electrical properties of interdigitated partially bent like shaped liquid crystalline compound

ABSTRACT This article represents the electrical studies of an interdigitated highly skewed N(4-n-pentyloxybenzylidene) 4-n-alkylaniline (5O.16) compound. Interestingly the compound is partially bent like and unsymmetrical in alkyl chain length. Dielectric and impedance spectroscopy studies indicate the coupling between the liquid crystal and the electrical field. Studies were carried out as a function of temperature as well as frequency. Semicircular nature of the Cole–Cole plots indicates the reorientation of the molecule with the applied field. Using the experimental data and the theoretically fitted results the effective equivalent model circuit was designed. Which used to explain the behavior of the compound under the external electric effect and the influence of the electrodes with different variable represent the resistor circuit. However, the effect of the conductivity of temperature and frequency are also reported.

Methanol sensing by SnO2 pellets prepared by chemical route method

Synthesis of SnO2 and SnO2-CuO doped nanoparticles were carried out using chemical co-precipitation method. The precursor was SnCl4.5H2O. The XRD, SEM and EDAX of the nanoparticles were done, and the particle size was confirmed to be within 40nm. The powdered nanoparticles were then pelletized under a pressure of 13 Mp. Methanol was sensed with the pellets using a customized setup for 25, 50, 75 and 100ppm concentrations. It was observed that the sensitivity (S = Ra/Rg) showed appreciable variation at 375 °C and 275 °C for 75ppm and 100ppm of methanol respectively.

Dielectric relaxation and birefringence study of 7.O5O.7 dimeric liquid crystal compound

Measurement of dielectric relaxation and birefringence phenomenon of dimeric liquid crystal compound with the dependence of temperature was reported in this paper. Homogeneous (HG) and homeotropic (HT) alignment of the cell are introduced to investigate the dielectric relaxation, activation energy and birefringence. Cole-Cole plots analyzed the dielectric relaxation of the dimeric compound. The observed Cole-Cole plots were semi-circular, and the relaxation mechanism obeys the non-Debye type of relaxation behaviour. Slater’s perturbation equations have been used to analysis the activation energy of the compound. The birefringence of the compound has positively anisotropy and thin prism mechanism was used to study the anisotropy of the compound.

HUMIDITY-DEPENDENT IMPEDANCE AND DFT ANALYSIS OF PURE AND Cu-DOPED SnO2 THIN FILMS

Tin Oxide has been explored for gas sensing and humidity sensing. In the present work, pure and copper-doped SnO2 is synthesized by controlled spray pyrolysis technique. The films are homogeneous throughout. Rietveld analysis confirms the absence of other phases due to doping. The optical property is studied using UV-Visible spectroscopy which shows a change in the band gap with the introduction of the dopant. An elaborate impedance analysis is carried which showed the effect of doping. Cu-doped thin film showed a faster drop in the impedance when exposed to humidity. Significant change in the cole–cole plot is observed indicating better sensitivity with the doped sample in comparison to undoped. Higher humidity level from 80 to 92 RH is studied as it is important to detect the same in air conditioning systems, electronic devices, aviation systems and food processing systems. The equivalent circuit also reveals that the adsorption of water molecules on the surface of the thin films changes the impedance characteristics. Levenberg–Marquardt algorithm is employed for the theoretical calculations and identifying the equivalent circuit. The charge transfer in the doped sample is subjected to lesser grain resistance according to theoretical calculation and experimental results. A density functional approach is employed to study the band structure and explain the influence of Cu doping on pure SnO2. The calculated result supports the use of Cu as a dopant for better humidity sensing device.