V.A. Rana

Synthesis, mesomorphism and dielectric behaviour of novel basket shaped scaffolds constructed on lower rim azocalix[4]arenes

A newly designed series of lower rim azocalix[4]arene basket type mesogens were synthesised and fully characterized. The proposed supramolecular organization displays needle shaped, rod like, focal conic and schlieren textures. These compounds were studied for their dielectric properties in the frequency range 100 Hz–2 MHz at variable temperatures (50–110 °C).

Dielectric study of novel liquid crystals based on calix[4]arene Schiff bases

Novel liquid crystals based on calix[4]arene Schiff bases have been synthesised by the reaction of tetra-amino-calix[4]arene with two aldehydes (4-hydroxy benzaldehyde and 4-vanillin), further substituted with alkyl chains (n-butyl bromide and n-octyl bromide) on both the upper and lower rim by substitution of the hydroxyl groups of the calix[4]arenes. These derivatives were purified and characterised by elemental analysis and Fourier transform infrared, 1H and 13C nuclear magnetic resonance and matrix-assisted laser desorption/ionisation time of flight mass spectrometry. The compounds were investigated for liquid crystalline properties using differential scanning calorimetry, differential thermal analysis, X-ray diffraction, and polarising optical microscopy with a heating assembly. All the compounds were found to exhibit nematic structure and a typical fanlike or mosaic texture, which suggests an ordered smectic mesophase. Dielectric investigations were also carried out and showed N, SmA and SmC phases. Dielectric permittivities (ϵ′ and ϵ″) were determined at a variety of temperatures (45–95°C) over a range of frequency between 20 Hz and 2 MHz.

The influence of linking group in exterior point on mesogenic properties of the basket moulded molecules: calix[4]arene

Novel basket-shaped molecules having calix[4]arene as central rigid core possessing azomaterial in outer space unit in the lengthening arm were synthesised and characterised by elemental analysis and different spectroscopic methods such as Fourier Transform Infrared (FT-IR), electron spin ionization (ESI)-MASS, 1H nuclear magnetic resonance (NMR) and 13C NMR. Mesomorphism behaviour of novel materials was studied using optical polarising microscopy, differential scanning calorimetry and higher-temperature powder X-ray diffraction method to confirm smectic C phase. In most of the compounds, we found rod-like mosaic texture and focal conic textures of smectic C phases. Nematic phases were also quite often found in materials during cooling and heating stage from isotropic phases. The dielectric measurements have been carried out for the determination of real and imaginary parts of the permittivity of the newly designed scaffolds. These studies will give adequate prospects in the field of supramolecular system, especially in calixarene organisation to explore new epoch of calixarene-based liquid crystals with different linking groups.

Cavity perturbation technique for complex permittivity measurement of dielectric materials at X-band microwave frequency

A cavity perturbation technique is presented for measurement of dielectric constant and dielectric loss of the dielectric materials at X-band microwave frequency. A tunable rectangular cavity to operate in TE103 mode was designed and fabricated. Tunable cavity is calibrated to read its resonance frequency directly from the micrometer screw arrangement attached with the cavity. Shift in resonance frequency (Deltafr) and quality factor (Q) of the cavity without and with dielectric material inside the cavity are measured. Using measured values of Deltafr and Q, dielectric constant and dielectric loss of the dielectric materials are determined.

Dielectric and Electrical Properties of Binary Mixtures of Anisole and Some Primary Alcohols in the Frequency Range 20 Hz to 2 MHz

The complex relative dielectric function ε*(ω) = ε-jε of binary mixture of anisole (AN) with methanol (MeOH) ,1-propanol (1-PrOH), 1-butanol (1-BuOH), 1-heptanol (1-HeOH) of varying concentration have been measured using Precision LCR meter in the frequency range 20 Hz to 2 MHz at 303 K. The electrical/dielectric properties of the liquid samples are represented in terms of intensive quantities namely, complex relative dielectric function ε*(ω), electrical modulus M*(ω), and extensive quantities, i.e. complex admittance Y*(ω) and complex impedance Z*(ω). All of these presentations are used to explore various processes contributed in the electrical/dielectric properties of the mixtures of polar-polar liquids.

Dielectric absorption in mixtures of anisole with some primary alcohols at microwave frequency

Dielectric properties of binary mixtures of anisole with methanol (MeOH), 1-propanol (1-PrOH), 1-butanol (1-BuOH) and 1-heptanol (1-HeOH) over an entire concentration range have been studied at a fixed temperature 40°C. The dielectric constant (ε′) and dielectric loss (ε″) of the binary mixtures of polar liquids have been determined at a microwave frequency of 9.1 GHz. The static dielectric permittivity (ε 0) of the liquid samples was also determined using a precision LCR meter. Determined values of static dielectric permittivity (ε 0) and dielectric permittivity (ε*) at 9.1 GHz frequency were used to evaluate relaxation time (τ) and high frequency limit dielectric permittivity (ε ∞). Dielectric parameters were interpreted in terms of molecular interaction between the anisole and alcohol molecules.

Dielectric Spectroscopy of Dry and Wet Soils in Frequency Region from 20 Hz to 20 GHz

The complex permittivity of a soil is a very much useful parameter in remote sensing applications. The measurement of complex permittivity of soil at various microwave frequencies can be related with the moisture content in the soil, which is useful in Agriculture, Hydrology and Meteorology. The complex dielectric spectra of dry and wet soil samples were measured in the frequency range from 20 Hz to 20 GHz. For this, various instruments and different methods were used. The complex permittivity of the soils, in the frequency range from 20 Hz to 2 MHz, was measured using a precision LCR meter, and a newly designed and developed coaxial capacitor probe. The complex permittivity of the soils, in the frequency range from 75 MHz to 1.5 GHz, was measured using a Vector Network Analyzer. The complex permittivity of the soils at 5.65 GHz, 9.5 GHz and 19.3 GHz was measured using microwave bench set up. The results are presented in the paper.

Dielectric Studies of Binary Mixtures of 1-Propanol and Fluorobenzene

Complex permittivity spectra of 1-Propanol (1-PrOH), Fluorobenzene (FB) and their binary mixtures are obtained in radio and microwave frequency range using Vector network analyzer (VNA) operating in the frequency range 0.3 MHz to 3.0 GHz and standard microwave benches operated at 9.1 GHz and 19.61 GHz. Static dielectric constant (ε0) and high frequency limiting dielectric constant (ε∞1) for binary mixtures of 1-PrOH and FB are obtained by extrapolating the complex permittivity data towards low frequency side and high frequency side on complex plane plots. Optical dielectric constant (ε∞ = n2) for binary mixtures are measured using Abbes refractometer. Excess static dielectric constant (ε0)E, Kirkwood correlation parameters (g, geff and gf) and Bruggeman factor (fB) are determined from the values of static dielectric constant (ε0) and optical dielectric constant (ε∞). These parameters have been discussed to explore the molecular interaction between the molecular species.

A Study of Molecular Interaction in Binary Mixtures of 1-Propanol with N,N-Dimethylformamide at Different Temperatures

The static dielectric constant (ε0) and optical dielectric constant (ε = n2) of binary mixtures of 1-Propanol (1-PrOH) with N,N-Dimethylformamide (DMF) of different concentrations, prepared by volume fractions (0.0, 0.1, . 1.0) are measured at 2 MHz using precision LCR meter and Abbes refractometer respectively at different temperatures. The excess dielectric constant (ε0)E, Kirkwood correlation parameters (geff, gF), Bruggeman parameter (fB) are evaluated. The variations of these parameters with concentration and temperature are discussed in terms of molecular interaction between the molecular species of constituting components in these mixtures.

Dielectric and Electrical Properties of Binary Mixtures of Anisole and 1-Heptanol in the Frequency Range 20 Hz to 2 MHz

The complex relative dielectric function ε*(ω) = ε’- jε” of anisole (AN), 1-heptanol (1-HeOH) and their binary mixtures of varying concentration have been measured using Precision LCR meter in the frequency range 20 Hz to 2 MHz at 303 K. The electrical/dielectric properties of the liquid samples are represented in terms of intensive quantities namely, complex relative dielectric function ε*(ω), electrical modulus M*(ω), electrical conductivity σ*(ω) and extensive quantities, i.e. complex admittance Y*(ω) and complex impedance Z*(ω). All of these presentations are used to explore various processes contributed in the electrical/dielectric properties of the mixtures of two polar liquids.