M. Johri

Dielectric and phase transition studies of 1MC1EPOPB ferroelectric liquid crystal

Abstract An experimental study for R — 4′-(1 methoxycarbonyl – 1 – ethoxy) phenyl 4 – (4 – octyloxyphenyl) benzoate (1MC1EPOPB) ferroelectric liquid crystal (FLC) using impedance analyzer and differential scanning calorimetric (DSC) technique is reported. The measurements have been done for permittivity, dielectric loss at different frequencies and temperatures. The data have been analyzed for distribution parameters involved in Havriliak-Negamis equation. The relaxation time measured for different relaxation processes is listed. The measurements for static dielectric constants in the parallel(ε∥) and perpendicular(ε⊤) directions at different temperatures have also been taken. The transition temperatures are identified for cooling and heating conditions using DSC technique as well as dielectric measurements. The interesting results have been found and some unknown phases have been monitored, the reason for which needs theoretical interpretation.

Study of the effect of temperature and magnetic field variation on dielectric properties of organic liquids using a microwave cavity spectrometer

Abstract The temperature and magnetic field variation have been studied for the dielectric properties of 2-chlorobutane, acetonitrile and nitrobenzene in their pure state using microwave cavity spectrometer at 9.0 GHz. The analysis of the observed data of width, shift and amplitude of resonance profile has been carried out by using Slater perturbation equations for the computation of relaxation time, activation energy and for the relative study of permittivity and dielectric loss. This work provides fruitful information about the macroscopic structure of the organic liquids chosen.

Experimental Study of Dielectric Relaxation in 4-Cyano-4-n-Hexyl Biphenyl Nematic Liquid Crystal

Abstract Microwave cavity spectrometer has been used to measure the width of resonant profile and the shift of the resonant frequency. The observed data are analyzed to determine permittivity, dielectric loss and relaxation time. The relative variation of dielectric loss and permittivity at different temperatures has been studied for the purpose to monitor the phase changes in the range 282°K to 314°K and to identify the transition temperatures. We have used two frequencies 9.0 GHz and 29.867 GHz to see the frequency dependence for the purpose to compare relaxation mechanism. The technique used is useful as it needs a small quantity (< 0.001 cm3) of the sample and provides fruitful information about the macroscopic structure of the liquid crystal. The transition temperatures are TC→N = 287.6°K and TN→I = 301.9°K.

Study of Dielectric Response of Aqueous Solutions of Copper Sulphate Using Microwave Cavityspectrometer

Abstract Dielectric relaxation study of aqueous solutions of copper sulphate (CuS04) using microwave cavity spectrometer is reported. A cylindrical microwave cavity operated in TM010 mode was loaded. The variations of the width of the resonance profile and shift of the resonance frequency were achieved by changing the volume of the sample in the cavity as a function of probe length at 29.567 GHz. Slater perturbation equations have been used to analyse the data for permittivity, dielectric loss and relaxation time. This work provides information about ion-ion interactions.

Measurement of the Intensity of Sonoluminescence, Subharmonic Generation and Sound Emission Using Pulsed Ultrasonic Technique

The measurement of the intensity of sonoluminescence, subharmonic generation and sound emission with different pulse parameters is reported using a new method of stimulating the acoustic cavitation effect at high frequency (700 kHz) with a low-frequency (20 kHz) ultrasonic field. It is found that stimulation enhances the intensity of sonoluminescence and subharmonic generation at reduced threshold transducer voltage and inverse pulse duty ratio, while sound emission is oppositely affected. The bi-frequency effect arises due to space–time interaction. This work contributes to the understanding of the mechanism of light emission and nonlinear behavior of bubble dynamics.

Dielectric response in dimethyl substituted pyridines using microwave cavity spectrometer

A study of the dielectric response of dimethyl substituted pyridines (lutidines) has been reported in the temperature range 293-323 K. The microwave cavity spectrometer has been used to measure the relative shift, width and amplitude of the resonance profile for the sample loaded in the cavity operated in TM/sub 010/ mode at a fixed frequency of 9.0 GHz. The Slaters perturbation equations are used to analyze the measured data and permittivity and dielectric loss have been obtained using interaction form factor. Significant effect in the dielectric response and interaction has been found due to change of the position of the -CH/sub 3/ functional groups.

EXISTENCE OF A PHOTONIC BAND GAP AND UNDERLYING PHYSICAL PROCESSES

Mechanisms of the overlapping of gaps due to a refractive index difference minimum and Anderson localization for photonic band gap (PBG) have been used and they give a refractive index contrast difference of less than two percent for X-, L-, and W-points of the Brillouin zone for the pseudogap. Another physical process for the existence of PBG is the use of scattering strength (er ≥ 1) for fcc lattice structure. We have found refractive index contrast in the range 2.41–14.21 for the existence of the complete photonic band gap for bound photons (er ≥ 1). The lowest limit to yield a gap is 2.41 for valence photons (er = 1) at volume filling fraction 85.5% for spherical air atoms and at 14.5% for dielectric spheres. This work is reported for the first time and it is useful for maintaining connectivity and for easier fabrication of photonic crystals.

An experimental study of collision broadening of rotational spectral lines of 13CH3 13C15N in the ground and nν8, n=1 and 2 vibrationally excited states at microwave frequencies

A double modulation microwave spectrometer was used to determine the linewidth parameter for some rotational components in the nν8 vibrations of methyl cyanide under 13C and 15N substitution. The linewidth parameters for self‐broadening of the ΔJ=2←1 rotational components for the ground, ν8, and 2ν8 vibrations were determined over a pressure range of 1–13 mTorr and at a temperature of 300 K. An experimental method is presented to correct for modulation broadening when high derivatives are used to extract the absorption profile information from the signals. The eighth derivative profile was explored to determine if the spectral line shape remains Lorentzian over a range of modulation levels from 10% of Δν to more than 100% of Δν. These tests showed that the ratio of inner to next inner peak separations, designated in this paper as Δ, of the eighth derivative was the same as that for an assumed Lorentzian line shape. Thus, line shapes were assumed to be Lorentzian for theoretical analysis of the derivative ...

Determination of Effective Potentials for Non-polar Liquids Using the Continuum Dielectric Model

Abstract The “effective potential” for each system, nitrogen, argon, krypton, xenon, methane, benzene, carbon tetrachloride, carbon disulfide, n-hexane and cyclohexane was calculated by using the Clausius-Mossotti, Onsager and Kirkwood reaction fields with Lennard-Jones and Kihara potential parameters assumed. It was found that the Kirkwood reaction field with an assumed Kihara potential is a useful technique to study interactions arising due to physical association and chemical bonding.

Measurement of permittivity and dielectric loss in 2,4-dimethyl substituted pyridine using microwave cavity spectrometer and time domain reflectometer

Microwave cavity spectrometer and time domain reflectometer is used to measure the permittivity and dielectric loss at different temperatures in 2,4-dimethyl substituted pyridine. The observed data of the width of resonance profile and the shift in the resonance frequency have been analyzed using Slater perturbation equations for cavity spectrometer. The dielectric parameters measured from the time domain reflectometer as a function of time at different temperatures have been transformed to frequency domain to obtain the permittivity and dielectric loss. The observed values of the permittivity and dielectric loss at 9.0 GHz are fitted in Slaters perturbation equations to obtain the form factor, which represents interactions. The relaxation time has been evaluated at different temperatures using the ratio of width and twice of frequency shift and thermodynamical parameters have been determined. This experimental study provides fruitful information about the bulk properties of 2,4-dimethyl substituted pyridine.