Dynamic Dielectric Properties Research Articles

Notiz: Dynamic Dielectric Properties of Some Alkylamino Ethoxylates

Abstract Nine ethoxylated (EO) alkyl amines, (CnH2n + 1) N(EO)x; H(EO)y H, with n = 10 to 16 and p = x + y = 7.6 to 14.5, were studied as pure liquids with respect to their dielectric relax­ ation behaviour over the frequency range 5 MHz to 36 GHz at 20 °C. The broad and structureless dielectric loss spectrum is similar for all samples. It can be described by a main lower frequency spectral component of Havriliak-Negami type plus two minor, higher frequency Debye type components. The relaxation parameters are reported. Dynamic Dielectric Properties of Some Alkylamino Ethoxylates

Equilibrium and Dynamic Dielectric Properties of Acrylate Polymers with (Phenyl)(4-chlorophenyl)methanone Groups in Their Structure

The curves describing the relaxation behavior of poly(4-(acryloxy)phenyl)(4-chlorophenyl)methanone at several frequencies present in the dielectric loss-temperature plane a p relaxation centered at -76 C at 10 Hz, whose activation energy shows a slight tendency to increase as the temperature goes up. The relaxation spectra exhibit an ostensible glass-rubber relaxation or a process centered at 106 C at 10 Hz, in which free charge conductivity and blocking electrode phenomena become dominant at frequencies below 10 Hz. An electric model is used to separate the dipolar response from conductivity contributions in the glass-rubber relaxation, and the dipole time correlation function for this process is obtained at several temperatures. The intramolecular correlation coefficient gintra, determined from dielectric measurements in solution, is somewhat larger than the coefficient g involving both intra- and intermolecular interactions, obtained from dielectric measurements in the bulk. A rotational state scheme is developed which gives a good account of the intramolecular dipolar correlation coefficient. Finally whereas the relaxation mechanisms involved in the glass-rubber relaxation seem to be governed by the volume, the conductive processes exhibit Arrhenius behavior.

Ferroelectric dynamic of some H-bonded crystals

Abstract The results of study on dynamic dielectric properties of some H-bonded crystals are presented. It is shown that relaxational soft modes are responsible for the ferroelectric phase transition in RbD2PO4, PbHPO4 and NH4HSeO4 and their contribution accounts for the static permittivity. Glass-like dielectric relaxation with temperature depended relaxation time τ was observed in the ferroelastic phase of Cs5D3(SO4)4. Non-Debye dielectric relaxations characteristic to ionic conductors were observed in the high-temperature phases of Cs5D3(SO4)4 and NH4HSeO4.

Stark effect spectroscopy of tryptophan

The change in permanent dipole moment (magnitude of delta mu) for the transition from the 1La state to the ground state of tryptophan is the key photophysical parameter for the interpretation of tryptophan fluorescence spectra in terms of static and dynamic dielectric properties of the surrounding medium. We report measurement of this parameter by means of electric field effect (Stark) spectroscopy for N-acetyl-L-tryptophanamide (NATA) in two solvents, the single tryptophan containing peptide melittin, and 5-methoxytryptophan. The values ranged from 5.9 to 6.2 +/- 0.4 Debye/f for NATA and melittin, where f represents the local field correction. The 1Lb magnitude of delta mu was much smaller. Application of Stark spectroscopy to these chromophores required decomposition of the near-UV absorption into the 1La and 1Lb bands by measurement of the fluorescence excitation anisotropy spectrum and represents an extension of the method to systems where band overlap would normally preclude quantitative analysis of the Stark spectrum. The results obtained for 5-methoxytryptophan point out limitations of this method of spectral decomposition. The relevance of these results to the interpretation of steady-state and time-resolved spectroscopy of tryptophan is discussed.

Dielectric relaxation in sodium bis(2-ethylhexyl)sulfosuccinate-water-decane microemulsions near the percolation temperature threshold.

The results of an extensive study of percolation in order to verify some theoretical predictions about percolation critical indices for changes in static and dynamic dielectric properties of a microemulsion as a function of temperature and frequency are presented in this paper. The dynamic behavior of the microemulsions was also studied in order to reveal the mechanisms that are responsible for dielectric polarization of the system. The measurements were made by means of the time domain dielectric spectroscopy method in the frequency range ${10}^{5}$\char21{}${10}^{10}$ Hz and at temperatures from 10 \ifmmode^\circ\else\textdegree\fi{}C to 40 \ifmmode^\circ\else\textdegree\fi{}C. It was shown in our study that critical indices for conductivity and dielectric permittivity have the values s\ensuremath{\approxeq}1.2 below and t\ensuremath{\approxeq}1.9 above the percolation threshold. The value for the critical index s is in agreement with a dynamic percolation picture. This confirms the idea that the mechanism responsible for the temperature dependence of conductivity and permittivity has the same origin. The numerical value of t indicates a percolation picture above the threshold; however, it does not provide information about the nature of percolation. The data treatment for the dynamic behavior of the microemulsions was carried out in the time domain in terms of dipole correlation functions. It was found that the correlation functions exhibit complex nonexponential relaxation behavior in the percolation region and must be deconvoluted into normal modes and represented as the sum of the simple exponential exp(-t/\ensuremath{\tau}) and nonexponential terms exp[-(t/\ensuremath{\tau}${)}^{\mathrm{\ensuremath{\beta}}}$].

Dielectric Properties of 4-Cyanobiphenyl in 1,4-Dioxane Solution

Abstract The static and dynamic dielectric properties o f the title system are reported for a concentration series from about 8 mmol/1 up to 2.3 mol/I at 20 °C. The apparent moment (4.2 D , extrapolated to infinite dilution) decreases with increasing concentration, the relaxation time increases proportional to viscosity, that is, somewhat steeper than usually observed. Com parison with other molecules suggests that these features are mainly due to the high dipole moment rather than being specifically related to the prolate shape o f the molecule. The broadening o f the spectrum toward the high frequency side, on the other hand, may be due to the molecular shape.

Solvent and temperature control of the reaction mechanism and efficiency in the electrogenerated chemiluminescence of rubrene

Electrogenerated chemiluminescence (ECL) from the annihilation of rubrene cation and anion radicals has been studied in several organic solvents at temperatures down to − 60°C. The reactants were generated using the triple-potential-step method. Feldberg plot analysis indicates that the emission results from the excited rubrene singlet state produced directly in the electron transfer reaction (S route) and/or from the efficient triplet—triplet annihilation (TTA). In the special case of rubrene the energy of the lowest triplet is almost exactly half that of the first excited single, and the formation of two triplet states (in a single electron transfer act) leads to an efficient TTA (TT route). ECL efficiencies (φ ecl in the range 0.01–0.10) have been interpreted in terms of the Marcus theory, taking into account both static and dynamic dielectric properties of the solvent as well as both electronic and vibrational excitations of the reaction products. The rate of the triplet—triplet up-conversion ( k upc = 1 × 10 10 s −1 within the rubrene triplet—triplet pair) has been also evaluated.

Dielectric Relaxation of Liquid Polyethyleneglycol on Addition of Polyvinylpyrrolidone

Abstract The set of relaxation times describing the dynamic dielectric properties of liquid polyethyleneglycol 200 at 20 and 40 °C is found to be practically independent of the admixture of polyvinylpyrrolidone, though the viscosity is appreciably increased. This is compared to the rather similar behaviour of small molecular solvents.

Electrochemical generation of excited TICT states. V. Evidence of inverted Marcus region

The electrogenerated chemiluminescence of intramolecular donor-acceptor compounds was studied in several organic solvents using the triple-step method. The compounds studied were aryl derivatives of N, N-dimethylaniline and 9-anthryl derivatives of aromatic amines. In the electrogenerated emission spectra only the twisted intramolecular charge-transfer (TICT) band was observed. The Feldberg plot analysis indicates that the emitting species are formed directly by the electron transfer between electrogenerated radical cation and radical anion (singlet route). High emission efficiences (φ ECL up to 0.05) as well as high yields of the emissive excited state (φ ES up to 0.21) have been found. The φ ES values obtained have been interpreted in terms of the Marcus theory, taking into account both static and dynamic dielectric properties of the solvent as well as both electronic and vibrational excitation of the reaction products. The main reaction channels are the adiabatic formation of excited TICT state (controlled by the solvent dynamics) and the non-adiabatic formation of the local excited triplets.

A dielectric theory of the optical-like high-frequency mode in liquid water

The ‘‘optical’’-like collective mode (OM) in TIP4P model water recently reported by Ricci et al. is investigated here with a simple dynamical theory, the reference memory function approximation (RMFA), applied to calculate the dynamical dielectric properties of rigid and nonpolarizable interaction site models for water. Our results indicate that the OM is responsible for the high-frequency local charge density fluctuations that are germane to the frequency- and wave vector-dependent longitudinal dielectric function of water. The results for the OM in the TIP4P and SPC/E water models studied here under RMFA are in good agreement with each other as well as with molecular dynamics simulation results of Ricci et al. on the TIP4P model. An interesting connection to ion solvation dynamics is established.

Dielectric Critical Slowing-Down in Ferroelectric Ca2Pb(C2H5CO2)6Crystal

Measurement of the complex dielectric constant of Ca 2 Pb(C 2 H 5 CO 2 ) 6 (DLP) has been made around the ferroelectric phase transition temperature, T c . The dielectric dispersion of relaxational type of which the relaxation time shows the critical slowing-down has been observed. The results indicate that the ferroelectric phase transition of DLP is essentially of the order-disorder type. No essential differences are found between DLP and isomorphic Ca 2 Sr(C 2 H 5 CO 2 ) 6 (DSP) in the static and dynamic dielectric properties around T c .

Ion size effects on the dynamic and static dielectric properties of aqueous alkali solutions

Dielectric spectroscopy studies of aqueous ionic solutions ACl/H2O (A=Li, Rb, Cs) were carried out at frequencies between 45 MHz and 20 GHz, using recently developed coaxial measurement techniques. The behavior of the static dielectric constant εs0 and the dielectric relaxation time τD of the solutions were studied as functions of ion size and concentration. For moderate concentrations both εs0 and τD decrease linearly with solution conductivity. While the behavior of εs0 can be understood in terms of either static or Hubbard–Onsager kinetic polarization models, the experimental results for τD are at present not understood quantitatively in terms of these models. However we point out the good correlation of the τD data with empirical viscosity results, which suggests an alternative explanation based upon the solution viscosity, modified by ion size effects, which play an important role in the dielectric response. We also discuss the various length scales relevant to dielectric and conductivity processes in the solutions.

Dielectric properties of polyamide-4,6

The dielectric properties of polyamide-4,6 were examined as functions of frequency, temperature and moisture content. The dielectric spectra were compared with the results of dynamic mechanical measurements in torsion at 0.2153 Hz, as a function of temperature, and with the dynamic dielectric properties of commercial polyamide-6,6. Three relaxation processes are observed in polyamide-4,6, which are related to either local or collective molecular mechanisms of motion, similar to the relaxation processes observed in other polyamides. At temperatures above the glass transition temperature, ionic conductivity is observed, which, due to the semicrystalline structure of the material, gives rise to a strong Maxwell—Wagner—Sillars (MWS) polarization. With increasing temperature, the conductivity increases sharply, eventually causing electrode polarization, and thus obscuring the dielectric effects in the material. All loss processes shift to lower temperatures with increasing water content. The activation energies of the secondary relaxations decrease with increasing water uptake, while the β and α relaxations are enhanced in magnitude.

Dielectric Relaxation of N‐Cyano Substituted Morpholine, Piperidine and Pyrrolidine

AbstractThe dynamic dielectric properties of the title substances are measured at 20 °C at frequencies up to 72 GHz in the pure liquid state and in mixtures (x = 0.4–1) with benzene and tetrachloromethane. Rotational tumbling motion of single (non‐associated) molecules is likely to be the main relaxation process. Peculiarities are found with two out of the six systems, namely mixtures of cyanopiperidine and cyanopyrrolidine with tetrachloromethane. These are discussed as possibly due to a concentration dependent conformational equilibrium.

Dielectric relaxation and a new phase of cyclooctanol at pressures to 1 GPa

On the four previously known solid phases of cyclooctanol (I, II, IV and V in our notation), two (IV and V) are stable only at high pressure. In this work, new data on dynamic dielectric properties of cyclooctanol at high pressure are presented. The results are compared with corresponding thermal conductivity data. It is concluded that the dielectric properties of phase II are consistent with the thermal conductivity properties if it is assumed that a substantial fraction of the dipoles interact with each other. The molecular interaction favours reorientation around an axis of negligible dipole moment. The new solid phase, phase III, which was discovered through thermal conductivity measurements, is detected dielectrically in the present study.

Dielectric Dispersion in Rb1-x[N(H1-yDy)4]x(H1-yDy)2PO4Mixed Crystal System

Temperature and frequency dependent dielectric responses of Rb 1- x [N(H 1- y D y ) 4 ] x (H 1- y D y ) 2 PO 4 (0.25≤ x ≤0.75, 0≤ y ≤1.0) have been measured from 4.2 K to 300 K and between 1 kHz and 1 GHz. The glass-like dielectric dispersion was found in the low temperature region. The relaxation time τ has been confirmed to follow the Vogel-Fulcher law, τ=τ 0 exp [ E /( T - T 0 )], with a temperature independent Gaussian distribution of energy parameter E . Pronounced effect of deuteration was found in the dynamical dielectric properties. On the contrary, there is no obvious x dependence in the dynamical properties. Little difference was observed in the dielectric dispersions along the a - and c -axes. These results indicate that proton motion in the O-H···O bond has decisive role in the glass-like behavior.

Pinning effect on microwave dielectric properties and soft mode in TlInS2and TlGaSe2ferroelectrics

Abstract This paper presents the results of an investigation of microwave dielectric dispersion in the proper semiconductive ferroelectrics TIInS2 and TIGaSe2 with an incommensurate structure modulation. In these crystals there is a strongly overdamped soft ferroelectric mode, whose frequency in the vicinity of the phase transitions drops to the millimetre wave region and causes dielectric microwave dispersion plus a high contribution to the static dielectric permittivity. Within the incommensurate phase crystal defects, such as impurities, cause pinning of the soft mode. Because of this pinning effect the phason frequency increases. Pinning also changes the dynamical dielectric properties and the contribution of the phason and amplitudon to the static permittivity.

Dynamic mechanical and dielectric properties of epoxidized SBS triblock copolymer

AbstractThe morphological and dynamic properties of epoxidized styrene–butadiene–styrene block copolymers were studied and compared with their parent styrene–butadiene–styrene block copolymer (SBS). Two peaks were observed in the mechanical loss (tan δ) curve which can be attributed to segmental motion of epoxidized polybutadiene (EPPB) and polystyrene. Analysis by DSC thermograms also showed the linear increase of glass transition temperature for EPPB domain with the epoxy group content. Phase separated structures of epoxidized SBS as observed by TEM suggests a considerable degree of mixing occurred between phases after 80 mol % of the double bonds in SBS were epoxidized. The interfacial region displays a third peak and causes much steeper drop in modulus at higher temperature than Tg of EPPB. Parallel dielectric relaxation measurements were also made in the frequency range of 30 Hz–1 KHz as a function of temperature. In each dielectric constant (ϵ′) curve, there is a maximum near the Tg of EPPB determined from the dielectric loss tangent curve. The shift in Tg of EPPB versus epoxy group content was consistent with that measured by the thermal and dynamic mechanic analysis. These findings indicated an 8°C shift in glass transition temperature as the epoxy group content in EPPB increased 10%.

Dielectric relaxation of benzophenone and some of its derivatives in the liquid state: Part III: 4—hydroxybenzophenone, 2,4—dihydroxybenzophenone and p—rosolic acid in propylenecarbonate solution

The dynamic dielectric properties of the title solutions have been measured between 20 MHz and 72 GHz at 20°C. They are discussed in terms of Debye type contributions. While the solute is likely to relax as single molecules in all cases, the solvent relaxation contains a particular slowed down contribution which is ascribed to loosely solvating molecules.

The Dielectric Relaxation of Water on Addition of Ethylene Carbonate and some Related Substances

Abstract The dynamic dielectric properties of diluted aqueous solutions of propylene carbonate, ethylene carbonate (EC). 4-butyrolactone and cyclohexanone (CH) have been measured at 20 °C. On assuming normal solute relaxation, the water relaxation can be described by two superimposed Debye type contributions, which may be interpreted in terms of a hydration model. Qualitatively, the influence on the water relaxation increases from EC to CH.