Dielectric properties of polyhydric alcohols: Butanediols

The equilibrium and dynamic properties of 1,3-, 1,4-, and 2,3-butanediols were studied experimentally in the frequency range from 1 MHz to 36 GHz at temperatures from 283 to 423 K. The densities of the compounds were measured. The Kirkwood correlation factor was calculated with various (experimentally measured and calculated) dipole moments of the molecules.     

Dielectric relaxation spectroscopy of macroporous IER beads suspensions dispersed in primary alcohols and water–ethanol mixtures

Dielectric measurements were first carried out on suspensions of ion-exchange resin beads dispersed in primary alcohols and water–ethanol mixtures in the frequency range 40 Hz–110 MHz. Due to the large bead radius, only Maxwell–Wagner (M–W) dielectric relaxations were observed. Regular dielectric behaviors were observed and phase parameters concerning constituent phases’ properties were determined through dielectric analysis, which revealed that the properties and the dispersing state of the bead are strongly dependent on the properties of dispersion medium. It is also found that dry beads cannot be completely soaked by alcohols with long aliphatic chain, and that suspension in water-rich mixture has similar dielectric behavior as in pure water due to the mixture's molecular construction. Then the dielectric behaviors of the following suspensions were measured as a function of time: suspensions of beads that have been equilibrated with water/ethanol redispersed in ethanol/water. The dielectric behaviors showed remarkable time dependency, characterized by distinct transitions on the curves of time dependent relaxation parameters. Based on the above understandings, the time dependent dielectric behaviors were analyzed in detail. It is showed that the time dependency directly reflected such processes as ion diffusion, solvent diffusion and solvent uptake that the systems undergo.     

Dielectric properties of multiatomic alcohols: 1,3-butanediol

The dielectric spectra of 1,3-butanediol in the temperature range of 298–423 K are analyzed using a variety of theoretical approaches. It is shown that the dielectric spectra of 1,3-butanediol are described by the Davidson–Cole equation. Conclusions as to possible mechanisms of dispersion are drawn using the Debye theory. The relaxation times of 1,3-butanediol, calculated in different ways, are compared. The dipole moments of clusters are calculated for the first time using the Dissado–Hill cluster model.     

Dielectric properties of polyfunctional alcohols: 2,3-butanediol

Using a variety theoretical approaches within the Debye, Davidson–Cole, and Forsman models, and an approach based on the Dissado–Hill theory, dielectric spectra of 2,3-butanediol in the temperature range of 298 to 423 K are analyzed. It is shown that the dielectric spectra of 2,3-butanediole are described by the Davidson–Cole equation, and the β_DC parameter depends strongly on temperature. The spectrum of dielectric relaxation of 2,3-butanediol within the Debye theory is presented as the sum of two areas of dispersion, and conclusions are drawn regarding possible mechanisms of dispersion responsible for the obtained fields. The relaxation times of 2,3-butanediol, calculated using different equations describing the nonlinear behavior of relaxation times, are compared. The dipole moments of clusters are obtained for the first time using the Dissado–Hill cluster model, and a preliminary analysis of them is performed.     

Dielectric spectroscopy of thixotropic dispersions

The full characterization of a dispersion requires measurement of the degree of dispersion and knowledge of the type of structuring assumed by the dispersed particles. Dielectric spectroscopy in the low frequency range is a promising experimental approach to this problem.     

Dielectric spectroscopy at microwave frequencies

A method is described which is capable of measuring the dielectric properties of liquids as a continuous function of frequency over the range 10 MHz to 18 GHz; an evaluation is made of its performance over the frequency range up to 4.2 GHz. The method described has substantial advantages in ease of operation and evaluation of results over the conventional “spot” frequency and time-domain spectrometer techniques.     

Dielectric spectroscopy of liquid crystalline dispersions

We describe dielectric spectroscopy measurements on dispersions of two thermotropic liquid crystals (5CB and 8CB) in a poly(dimethylsiloxane) matrix. 5CB exhibits nematic and isotropic phases, while 8CB exhibits smectic, nematic, and isotropic phases. The spectra of the dispersions exhibit a temperature-dependent dielectric relaxation in the interval from 100 to 1000 Hz, with relaxation times that depend strongly on whether the dispersed phase is isotropic, nematic, or smectic. The dielectric relaxation times also depend on the viscosity of the matrix fluid. These results suggest a coupling between the electric field and the mechanics of the interface that affects the spectrum of the dispersed phase and shifts the Maxwell-Wagner interfacial polarization peak.     

Dielectric spectroscopy of bidisperse colloidal suspensions

Tuning the luminescence intensity of fluorophores using nanoparticles has shown great potential for the detection of inorganic metal ions, viruses, and proteins. The enhancement or quenching of a dye's fluorescence intensity is strongly dependent on the spatial separation of the dye from the nanoparticle surface. To extend luminescence probing from the solution platform to the solid-state platform, we explored and performed dye quenching assessment using an array format in this study. We report the distance-dependent fluorescence behavior of Au-DNA conjugates prepared by equilibrating phosphine-stabilized gold nanoparticles (AuNPs) of 10-nm size with the designed spacer ds-DNA consisting of thiol-modified target and Cy3-labeled complementary probe of different lengths (5-20 nm). The Cy3-labeled products were immobilized onto MPTMS (3-mercaptopropyltrimethoxysilane)-modified glass substrates and then excited with a 532-nm laser source. Quenching efficiency of AuNPs with increasing Au-to-dye distance was assessed using ligand exchange of the thiolated oligonucleotide by 2-mercaptoethanol (ME) to obtain free Cy3-DNA probe, thus eliminating nanoparticle effect on the dye's luminescence intensity. Effective exchange, revealed by UV-vis absorption and fluorescence profiles, was achieved in a few minutes. It was observed that fluorescence quenching of Au-DNA-Cy3 assessed using the array format was consistent with the result in solution phase for the conjugates with up to 10-nm Au-to-Cy3 separation distance.     

Dielectric spectroscopy of aminoalcohols and polyethylenepolyamines

Dependences of dielectric permittivity ?(f) and dielectric loss tangents tansδ(f) of aminoalcohols (AAs), polyethylenepolyamines (PEPAs), water, and aqueous solutions of AAs and PEPAs with water concentrations of 1 wt % are investigated in the frequency range of 0.025–1000 kHz. The dielectric relaxation of the liquids under study is investigated. An interrelation between the dielectric parameters and physicochemical properties of AAs and PEPAs is established. Empirical equations that describe this interrelation with a high degree of accuracy of approximation validity are derived. The effect of water on the dielectric characteristics of AAs and PEPAs is shown. It is suggested that we evaluate the energy of affinity of AAs and PEPAs for water using the coefficient of dielectric losses ?″.     

Dielectric spectroscopy of a smectic liquid crystal

Complex dielectric spectroscopy (frequency range 5 Hz-13 MHz) has been used to analyse the frequency, temperature and bias-field dependences of the molecular dynamics of a very high-spontaneous-polarization ferroelectric liquid crystalline material exhibiting SmA, SmC* and unknown SmX smectic phases. Different smectic phase transition temperatures have been observed from the study of the temperature dependence of the dielectric strength and the relaxation frequency. The phase transition temperatures (crystalline to isotropic phases) have also been described very accurately from the temperature-dependent symmetric and asymmetric shape parameters of the relaxation function and also the dc conductivity. In a planar aligned cell, two symmetric modes (Goldstone mode and domain mode) have been observed in both the SmX and SmC* phases. One asymmetric mode (X-mode) observed in the SmC* and SmA phases could be related to the interaction of dipoles of the ferroelectric liquid crystals being affected by the surface of the cell. The soft mode, which usually appears very close to the SmC*-SmA phase transition was not observed until the bias field was applied. The second order nature of the SmC*-SmA phase transition was revealed.     

Dielectric spectroscopy of Anabaena 7120 protoplast suspensions

The dielectric spectroscopy of Anabaena 7120 protoplast suspensions has been investigated over the frequency range of 40 Hz-110 MHz. The protoplast suspensions showed a complicated dielectric dispersion consisting of at least four distinct sub-dispersions with the increasing frequencies due to the Maxwell-Wagner interfacial polarization. The double-shell model, in which an equivalent shell of thylakoid was assumed inside the cytoplasm, was adopted to describe the special morphology of the protoplast. Under the assumption that the conductivity of plasmalemma was negligible and the conductivity of the equivalent shell was 0.1 microS/cm, we attempted to estimate the dielectric properties of various protoplast components by fitting theoretical curve to experimental data. The relative permittivity of the plasmalemma epsilon(mem) was estimated to be 6.5+/-0.5, and the permittivity of the equivalent shell of thylakoid epsilon(thy) was estimated to be about 3.2+/-0.2. The permittivity epsilon(cyt) and conductivity kappa(cyt) of the cytoplasm were estimated to be 60 and 0.88+/-0.11 mS/cm, respectively. The permittivity epsilon(nuc) and conductivity kappa(nuc) of the nucleoplasmic region were determined to be 100 and 0.13+/-0.02 mS/cm, respectively.     

Dielectric spectroscopy of a smectic liquid crystal

Complex dielectric spectroscopy (frequency range 5 Hz–13 MHz) has been used to analyse the frequency, temperature and bias‐field dependences of the molecular dynamics of a very high‐spontaneous‐polarization ferroelectric liquid crystalline material exhibiting SmA, SmC* and unknown SmX smectic phases. Different smectic phase transition temperatures have been observed from the study of the temperature dependence of the dielectric strength and the relaxation frequency. The phase transition temperatures (crystalline to isotropic phases) have also been described very accurately from the temperature‐dependent symmetric and asymmetric shape parameters of the relaxation function and also the dc conductivity. In a planar aligned cell, two symmetric modes (Goldstone mode and domain mode) have been observed in both the SmX and SmC* phases. One asymmetric mode (X‐mode) observed in the SmC* and SmA phases could be related to the interaction of dipoles of the ferroelectric liquid crystals being affected by the surface of the cell. The soft mode, which usually appears very close to the SmC*–SmA phase transition was not observed until the bias field was applied. The second order nature of the SmC*–SmA phase transition was revealed.     

Dielectric spectroscopy of some heteronuclear amino alcohol complexes

The temperature dependent dielectric spectroscopic properties of two heteronuclear complexes of monoethanolamine (MEA) at a wide temperature range (303-413 K) were investigated by impedance spectroscopy, in the frequency range from 100 Hz to 100 kHz. The frequency dependence of the impedance spectra plotted in the complex plane shows semi-circles. The Cole-Cole diagrams have been used to determine the molecular relaxation time, tau. The temperature dependence of tau is expressed by thermally activated process. Relaxation frequencies corresponding to the rotation of the molecules about their long axes are expected to lie above 10 MHz and exhibit Arrhenius behavior, where a single slope is observed with activation energy values equal to 0.67 and 0.78 eV. The ac conductivity sigma(ac) (omega) is found to vary as omega(s) with the index s相似文献   

Submillimetre laser and interferometric spectroscopy of the alkyl alcohols

The far-infrared power absorption of a series of alkyl alcohols has been measured with interferometry and laser spectroscopy. The two techniques are complementary and in good agreement. The vibrational COH torsion and O...H stretch have been analysed, particularly for methanol in dilute solutions.     

Dielectric spectroscopy and molecular theory of aligned nematics

The reorientation in the liquid crystal mesophase of a molecular dipole vector (μ) is coupled analytically to the centre of mass translational velocity (v). The resulting equations for the complex permittivity (ε*) contain three phenomenological friction parameters, γ_μ, γ_ν and γ_μνγ_νμ. Here γ_μ is the orientational friction, γ_ν that opposing the centre of mass translation and γ_μνγ_νμ a product of coupling frictions (off diagonal elements of the tensor γ). The Cole-Cole plot of ε* can be flattened, split and skewed using different combinations of the elements of γ. It is possible to obtain more than one relaxation time from a given rotational friction γ_μ provided that the orientational/translation coupling is properly accounted for. The theory is developed to include inertial and memory effects. Dielectric phenomena across the nematic to isotropic phase transition are reproduced in a natural manner by taking into account the fact that when the macroscopic sample becomes isotropic the autocorrelation functions <μ(0)·v(t> and <v(0)·μ(t)> vanish using symmetry rules concerning parity, reflection and time reversal.     

Dielectric spectroscopy study of cyanate ester oligomer curing kinetics

The evolution of dielectric properties during the cyanate ester oligomer curing process was studied in the electric field frequencies range of 10^–2—10⁵ Hz. The kinetic of the curing process was investigated using the acquired data for complex dielectric permittivity and conductivity. It is demonstrated that, along with the formation of the polymer network, a microphase separation of the reaction intermediate, namely carbamate, takes place during the trimerization reaction. It is manifested in the frequency spectra as the Maxwell—Wagner polarization.     

Dielectric relaxation spectroscopy of amorphous and liquid-crystalline side-chain polycarbonates

The molecular dynamics of amorphous and liquid-crystalline (LC) side-chain polycarbonates was studied by dielectric spectroscopy at frequencies from 10⁻² to 10⁶ Hz and at temperatures from −160 to 180°C. ‘Model’ compounds containing no mesogenic side-groups showed two relaxations, which originate from the carbonate group (α, β_m-relaxation). By contrast, in LC-polycarbonates bearing a mesogenic nitrostilbene side group around and above the glass transition temperature T_g up to three relaxation modes were distinguished (α-, λ₁-, λ₂-process); below T_g four secondary relaxations (γ-, β_m-, β_s-, β_sc-relaxation) were observed. The γ-relaxation was found only in compounds possessing an aliphatic spacer linked to the backbone by an ether bond. Apart from β_m-, two additional β-processes were identified as relaxations associated with the mesogenic unit in the glassy (β_s) or in the crystalline state (β_sc).     

Chiral discrimination of aliphatic amines and amino alcohols using NMR spectroscopy

Two methods are compared for analyzing the enantiomeric purity of aliphatic amines and amino alcohols using NMR spectroscopy. The first employs (+)‐(18‐crown‐6)‐2,3,11,12‐tetracarboxylic acid as a chiral NMR solvating agent in methanol‐d₄. The second involves a derivatization scheme in which the amine is reacted with naphtho[2,3‐c]furan‐1,3‐dione to form the corresponding amide. The naphthyl amide is then mixed with a chiral calix[4]resorcinarene in deuterium oxide. The crown ether only produces sufficient enantiomeric discrimination to determine enantiomeric purity for three of the nine substrates studied. The system with the naphthyl amide and a calix[4]resorcinarene produces enantiomeric discrimination of sufficient magnitude to determine enantiomeric purity for all nine substrates. The H1 and H4 resonances of the naphthyl ring are especially suitable to monitor for enantiomeric discrimination. The order of the (R)‐ and (S)‐enantiomers of the H1 and H4 resonances exhibit specific trends for aliphatic amines and amino alcohols that correlate with the absolute configuration. Copyright © 2012 John Wiley & Sons, Ltd.