Dielectric Dispersion Studies Research Articles

Calorimetric, dielectric, infrared spectra and thermal expansion studies of structural phase transitions in ((CH3)2CHNH3)2MX5 (M=Sb, Bi; X=Cl, Br) crystals

Differential scanning calorimetric, thermal expansion, dielectric dispersion, infrared and preliminary x-ray diffraction studies on ((CH3)2CHNH3)2MX5 (M=Sb, Bi; X=Cl, Br) crystals are reported. All the studied salts are isomorphous, crystallizing in monoclinic symmetry. They undergo low-temperature structural phase transitions of first and second-order type: ((CH3)2CHNH3)2SbBr5 at 171 and 180 K, ((CH3)2CHNH3)2BiCl5 at 164 K, ((CH3)2CHNH3)2BiBr5 at 155 and 133 K. Dielectric dispersion studies in all isopropylammonium crystals between 100 Hz and 1 MHz reveal a low-frequency relaxation process described by the Cole-Cole formula with alpha approximately=0.15-0.20 in the phase transition temperature region. All phase transitions are likely to be due to the motion of the isopropylammonium cations.

Structural Phase Transitions in (n-C3H7NH3)2SbBr5

Abstract Dielectric, DSC, thermal expansion and preliminary X-ray diffraction studies on (n-C3H7NH3)- SbBr5 are reported. It was found that this crystal undergoes a complex sequence of phase transitions. On cooling: phase I → phase II at 188.7 K (continuous), II → III at 165 K (1st order, ΔS = 26.8 J/mol K), III → IV at 137 K (1st order, 1.6 J/mol K). On heating: IV → III at 154 K, III → II’ at 168 K, II’ → II at 177 K (1st order, 2.8 J/mol K), II → I at 189 K. All 1st order phase transitions are likely due to the motion of the n-C3H7NH3 +cations. The dielectric dispersion studies between 100 Hz-1 MHz within the phases I and II indicate a fast reorientational motion of dipoles with τ < 10−7 S.

Dielectric relaxation in o-chlorobenzaldehyde and o-methoxybenzaldehyde at microwave frequencies

Dielectric dispersion studies of o-chloro- and o-methoxy-benzaldehyde in dilute solutions of benzene and p-xylene have been carried out at spot frequencies in the x- and k-band microwave frequency region at 35 °C. The dispersion curves for these molecules in both the solvents have been resolved into two distinct Debye-type curves. The relaxation time and weight factor corresponding to overall rotation of the molecule and group rotation have been determined by extrapolation of the curves. The molecular dipole moment, the dipole moment corresponding to overall rotation of the molecule and of the group rotations have also been evaluated using the Higasi equation. The ratio of weight factors for the two relaxation processes obtained from dispersion loci is in good agreement with that obtained from dipole moment data for these molecules.

Dielectric Behavior near a Smectic Ad- Smectic A2 Critical Point

Abstract We present precise measurements of the static dielectric constant near the smectic Ad-smectic A2 critical point in a binary system. Detailed analysis of the data obtained for several mixtures has been done to locate the critical point concentration. Results of a dielectric dispersion study near the Ad-A2 transition are also presented.

Dielectric behaviour and molecular association in monoalkyl ethers of ethylene glycol and of diethylene glycol in pure liquid state

Dielectric dispersion studies in monoalkyl ethers of ethylene glycol and of dlethylene glycol have been carried out in microwave frequency region in pure liquid state. Normalized complex plane plots have been plotted for these compounds. These are Cole-Cole arcs. Macroscopic relaxation time τ m and distribution parameter α have been calculated from these arcs. The probable nature of the reaction field has been discussed in these molecules by comparison of the ratio of experiment macroscopic and microscopic relaxation times for overall rotation with the theoretical value.

Dielectric relaxation in mono alkyl ethers of diethylene glycol at microwave frequencies

Dielectric dispersion studies in monoalkyl ethers of diethylene glycol (carbitols) have been carried out in microwave frequency region in dilute solutions of benzene. Complex plane plots (a″ vs a′) have been plotted by using the slopes of permittivity (ε′) and dielectric loss (ε″) vs. concentration. Average dielectric relaxation (τ 0) and distribution parameter (α) have been calculated. Data has been analysed in terms of two relaxation processes i.e., corresponding to overall rotation (τ 1) and group rotations (τ 2). Thermodynamic parameters and dipole moment of these molecules have been evaluated. Probability of intramolecular and intermolecular hydrogen bonding in these molecules has been discussed.

Dielectric Dispersion in Ag 6I 4WO 4 and Ag 6I 4CrO 4 solid elecrolyte thin films

This paper deals with the dielectric measurements made on the electrodeposited films of the solid electrolyte systems Ag 6I 4WO 4 and Ag 6I 4CrO 4. Dielectric dispersion studies have been carried out in the frequency range 10 3 to 10 5 Hz at various temperatures (300 to 400 K). The frequency dependence of dielectric constant has been attributed to the interfacial polarization of Ag + ions in these compounds. The observed dielectric loss behavior suggest a Debye-type of relaxation in these systems.

Molecular shape and dipole moment of alamethicin-like synthetic peptides

The peptides Boc-(L-Ala-Aib-L-Ala-Aib-L-Ala)n-OMe, with n = 2 (P10) and n = 4 (P20), have been synthesized as purely hydrophobic models of the antibiotic alamethicin, which is known to be a voltage-dependent pore former in membranes and is apparently alpha-helical in lipophilic media. These peptides were investigated in 1-octanol, a solvent which resembles the membrane environment. From dielectric dispersion studies quantitative information on the molecular shape and dipole moments could be derived. Further independent data concerning conformation and extent of aggregation of the peptides were obtained by circular dichroism and ultracentrifuge measurements. The results suggest that the peptides assume the form of elongated particles having a significant amount of ordered secondary structure and carrying a dipole parallel to the long axis. Apparently the monomeric peptide molecules undergo, to some extent, a head-to-tail aggregation which is slightly enhanced at lower temperatures. Based on the high-frequency parts of the dielectric dispersion curves the lengths, diameters, and dipole moments of the monomer particles have been determined as 22.5A, 10A, 36 D (P10) and 28.5A, 12A, 64D (P20).

Dielectric dispersion studies of some unsaturated compounds in dilute solutions

The dielectric permittivity and dielectric loss of solutions of four unsaturated triple-bonded compounds were measured as a function of frequency (10 kHz, 8.43, 11.3 and 35.6 GHz), temperature (33–70 °C) and concentration (0.07–0.01 weight fraction). The data are analysed in terms of a double relaxation process. The most probable relaxation time, the overall molecular relaxation time and the group relaxation time were calculated. The dipole moments were also calculated along with the thermodynamic parameters. The results are discussed in terms of association effects in these compounds and the dielectric data are correlated with the infrared spectral data.

Self-association of hemoglobin: a dielectric dispersion study.

AbstractThe concentration dependence of the dielectric dispersion between 1 kHz and 0.5 MHz was investigated for dense hemoglobin solutions. The concentration was varied between 4 and 26 mM/l. per heme. From the characteristic changes in dielectric parameters at some threshold concentration, we observe that the association of hemoglobin macromolecules occurs. This statement is also confirmed by viscosity measurement data.

ChemInform Abstract: DIELECTRIC DISPERSION STUDIES OF SOME INTRAMOLECULAR HYDROGEN BONDED MOLECULES AT MICROWAVE FREQUENCIES

Chemischer InformationsdienstVolume 8, Issue 37 Physical Organic Chemistry ChemInform Abstract: DIELECTRIC DISPERSION STUDIES OF SOME INTRAMOLECULAR HYDROGEN BONDED MOLECULES AT MICROWAVE FREQUENCIES H. D. PUROHIT, H. D. PUROHITSearch for more papers by this authorS. KUMAR, S. KUMARSearch for more papers by this authorA. D. VYAS, A. D. VYASSearch for more papers by this author H. D. PUROHIT, H. D. PUROHITSearch for more papers by this authorS. KUMAR, S. KUMARSearch for more papers by this authorA. D. VYAS, A. D. VYASSearch for more papers by this author First published: September 13, 1977 https://doi.org/10.1002/chin.197737042AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinkedInRedditWechat No abstract is available for this article. Volume8, Issue37September 13, 1977 RelatedInformation

A Numerical Inversion of the Perrin Equations for Rotational Diffusion Constants for Ellipsoids of Revolution by Iterative Techniques

The rotational diffusion coefficients R(1) and R(3) for ellipsoids of revolution are shown to represent another pair of hydrodynamic data to obtain size and shape with theories by Sadron and Scheraga-Mandelkern. An iterative numerical technique is presented which allows the semiaxes to be determined from the Perrin equations for rotational diffusion constants. The use of this inversion technique is illustrated by application to literature data from dielectric dispersion studies.