烷基聚葡糖苷C9.6G1.3/n-C4H9OH/n-C6H14/H2O微乳液体系的介电弛豫谱研究

The pseudotertiary phase diagram of the microemulsion system alkyl polyglucoside/n-butanol/n-hexane/water was plotted at （30.0±0.1） ℃. The dielectric measurements, including permittivity, conductivity, relaxation strength, characteristic relaxation time, etc,, were applied to investigate the microstructure of the system. Unique dielectric relaxations were observed over the frequency range of 5-10^7 Hz, taking place possibly through an interracial polarization mechanism. According to the results obtained from dielectric spectroscopy, the structures of the microemulsion O/W, BC and W/O were determined, and some dielectric and phase parameters were calculated.     

Study of the dynamics of water/aerosol OT/n-heptane system by dielectric relaxation measurements

Most of the previous dielectric studies on microemulsions and related systems have been conducted at relatively low frequencies where the dielectric response is sensitive to dynamic percolation phenomena. There is a lack of experimental studies at microwave frequencies where water plays a central role in dielectric relaxation. In this paper the dielectric complex permittivity of water/Aerosol OT/n-heptane microemulsions has been measured by a frequency domain coaxial technique in the range 0.02–20 GHz as a function of molar ratioW = [water]/[AOT] at low volume fraction of the dispersed phase (=0.1 and =0.2). The data show two dielectric dispersions: The first located in the 100 MHz frequency region and the second at frequencies higher than 20 GHz. The evolution of the dielectric parameters of these relaxations has been studied as a function of the molar ratioW in the range 0<W<28.     

基于太赫兹透射光谱的乙醇水溶液Debye模型研究

利用太赫兹透射光谱测量了液态乙醇和液态水以及不同浓度乙醇水溶液在22℃的介电常数.并利用Levenberg-Marquardt算法拟合得到了它们的Debye模型,该模型包含3个弛豫过程和1个分子间伸缩振动模式.其中,慢速弛豫模式的强度(弛豫时间20~160ps)贡献了主要的介电强度,中间弛豫模式与其密切相关.而快速弛豫模式(弛豫时间约为1ps)只占了大约5%的介电常数.     

Dielectric properties of water/lecithin/cyclohexane gels

Dielectric relaxation measurements in the frequency range 0.1–15 GHz have been carried out on water/lecithin/cyclohexane gels using a time domain reflectometry method (TDR). Dielectric dispersions describable in terms of a power law typical of percolated systems, but with exponents significantly different from those characterizing statically or dynamically percolated systems are observed. The dielectric dispersions, attributed to water and/or lecithin head group rotational motions, indicate that these motions are characterized by a wide spectrum of relaxation times.     

浓差极化的介电模型——复合膜/溶液体系的数值模拟

提出了具有电导率和介电常数线性分布的介质的介电模型, 并导出了其内部电的和结构性质的参数与宏观测量的电容和电导之间定量关系的理论表达式, 以模拟复合膜中的多孔层部分的介电弛豫行为. 大量的模拟计算描述并解释了多孔层介电谱随介电常数分布、厚度等性质而变化的规律. 进一步对具有层状构造的复合膜以及复合膜和溶液相组成的多层体系的弛豫行为进行了数值模拟, 比较了三个体系(多孔层、复合膜、复合膜/液相层状体系)的介电谱, 结果揭示了介电谱对各层性质的依赖关系. 所提出的电导率和介电常数线性分布的多孔层的介电模型, 也可用于具有其他电导率、介电常数分布规律的体系.     

Dielectric model and theoretical analysis of cationic reverse micellar solutions in CTAB/isooctane/n-hexanol/water systems

Dielectric relaxation spectra of CTAB reverse micellar solutions, CTAB/isooctane/n-hexanol/water systems with different concentrations of CTAB and different water contents, were investigated in the frequency range from 40 Hz to 110 MHz. Two striking dielectric relaxations were observed at about 10(4) Hz and 10(5) Hz, respectively. Dielectric parameters were obtained by fitting the data using the Cole-Cole equation with two Cole-Cole dispersion terms and the electrode polarization term. These parameters show different variation with the increase of the concentration of CTAB or the water content. In order to explain the two relaxations systematically and obtain detailed information on the systems and the inner surface of the reverse micelles, an electrical model has been constituted. On the basis of this model, the low-frequency dielectric relaxation was interpreted by the radial diffusion of free counterions in the diffuse layer with Grosse model. For the high-frequency dielectric relaxation, Hanai theory and the corresponding analysis method were used to calculate the phase parameters of the constituent phases in these systems. The reasonable analysis results suggest that the high-frequency relaxation probably originated from the interfacial polarization. The structural and electrical information of the present systems were obtained from the phase parameters simultaneously.     

Dielectric relaxations of chitosan: The effect of water on the α‐relaxation and the glass transition temperature

In this work thermal relaxations of chitosan are reported by using a novel methodology that includes subtraction of the dc conductivity contribution, the exclusion of contact and interfacial polarization effects, and obtaining a condition of minimum moisture content. When all these aspects are taken into account, two relaxations are clearly revealed in the low frequency side of the impedance data. We focus on the molecular motions in neutralized and non‐neutralized chitosan analyzed by dielectric spectroscopy in the temperature range from 25 to 250 °C. Low and high frequency relaxations were fitted with the Havriliak and Negami model in the 10^?1 to 108 Hz frequency range. For the first time, the low frequency α‐relaxation associated with the glass‐rubber transition has been detected by this technique in both chitosan forms for moisture contents in the range 0.05 to 3 wt % (ca. 18–62 °C). A strong plasticizing effect of water on this primary α‐relaxation is observed by dielectric spectroscopy and is supported by dynamic mechanical analysis measurements. In the absence of water (<0.05 wt %) the α‐relaxation is obscured in the 20–70 °C temperature range by a superposition of two low frequency relaxation processes. The activation energy for the σ‐relaxation is about 80.0–89.0 kJ/mol and for β‐relaxation is about 46.0–48.5 kJ/mol and those values are in agreement with that previously reported by other authors. The non‐neutralized chitosan possess higher ion mobility than the neutralized one as determined by the frequency location of the σ‐relaxation. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 2259–2271, 2009     

Dielectric relaxation study of glycine–water mixtures using time domain reflectometry technique

The complex permittivity of glycine in water mixture for various temperatures and concentrations have been measured as a function of frequency between 10?MHz and 30?GHz using time domain reflectometry technique. Dielectric parameters, i.e. static dielectric constant and relaxation time were obtained from the complex permittivity spectra using nonlinear least square fit method. The dielectric relaxation parameter increases with an increase in molar concentration of glycine due to the formation of hydrogen bond groups by glycine molecule in an aqueous solution medium. The activation entropy, activation enthalpy and Kirkwood correlation factor have also been determined for glycine–water mixtures.     

Depolarization thermocurrent studies in poly(hydroxyethyl acrylate)/water hydrogels

Detailed investigations on the dielectric relaxation mechanisms in poly(hydroxyethyl acrylate) (PHEA), by means of the thermally stimulated depolarization currents (TSDC) method in the temperature range 77-300 K are reported. There is particular interest in the dependence of the dielectric relaxation mechanisms on the water content h, h = 0 ? 0.5 w/w, in an attempt to contribute to a better understanding of the physical structure of water in the PHEA hydrogels. We employ thermal sampling (TS) and partial heating (PH) techniques to experimentally analyze the observed complex relaxation processes, due to the secondary (β_sw) and the main (α) relaxation, into approximately single responses and to determine the spectra of activation energies E(T) at different h values. Measurements with different electrode configurations reveal different aspects of the dynamics of the relaxation mechanisms and allow the distinction between dipolar and conductivity relaxation contributions. It is shown that by means of these techniques we can determine certain temperature characteristics for the α relaxation and investigate their dependence on water content. We discuss the relation of these characteristic temperatures to the calorimetric glass transition temperature T_g. © 1994 John Wiley & Sons, Inc.     

Dielectric relaxation spectroscopy in poly(hydroxyethyl acrylates)/water hydrogels

The electrical and dielectric properties of poly(hydroxyethyl acrylate), PHEA, hydrogels were studied by means of dielectric relaxation spectroscopy in wide ranges of frequencies (5–2 × 10⁹ Hz), temperatures (173–363 K) and water contents (0.065–0.46, g of water per gram of dry material). The secondary dipolar mechanisms (γ and β_sw) and the dc conductivity mechanism were studied in detail by analyzing the dielectric susceptibility data within the complex permittivity formalism, the modulus formalism, and the complex impedance formalism. For both mechanisms molecular mobility was found to increase with increasing temperature or increasing water content (T-f-h superposition principle). The energy parameters and the shape parameters of the response were determined for both mechanisms at several water contents and temperatures. The temperature dependence of dc conductivity was found to change from Vogel-Tamman-Fulcher (VTF) type to Arrhenius type at water contents of ca. 0.30. At water contents lower than about 0.30 the hydrogels are homogeneous whereas at higher water contents a separate water phase appears. In terms of the strong/fragile classification scheme our results suggest that the PHEA hydrogels are fragile systems. ©1995 John Wiley & Sons, Inc.     

Broadband dielectric spectroscopic, calorimetric, and FTIR-ATR investigations of D-arabinose aqueous solutions

The dielectric relaxation behavior of D-arabinose aqueous solutions at different water concentrations is examined by broadband dielectric spectroscopy in the frequency range of 10(-2) -10(7) Hz and in the temperature range of 120-300 K. Differential scanning calorimetry is also performed to find the glass transition temperatures (T(g)). In addition, the same solutions are analyzed by Fourier transform infrared (FTIR) spectroscopy using the attenuated total reflectance (ATR) method at the same temperature interval and in the frequency range of 3800-2800 cm(-1). The temperature dependence of the relaxation times is examined for the different weight fractions (x(w)) of water along with the temperature dependence of dielectric strength. Two relaxation processes are observed in the aqueous solutions for all concentrations of water. The slower process, the so-called primary relaxation process (process-I), is responsible for the T(g) whereas the faster one (designated as process-II) is due to the reorientational motion of the water molecules. As for other hydrophilic water solutions, dielectric data for process-II indicate the existence of a critical water concentration above which water mobility is less restricted. Accordingly, FTIR-ATR measurements on aqueous solutions show an increment in the intensity (area) of the O-H stretching sub-band close to 3200 cm(-1) as the water concentration increases.     

Influence of CTAB/alkanol/cyclohexane w/o microemulsions on the basic hydrolysis of crystal violet

The basic hydrolysis of crystal violet has been studied in w/o microemulsions of the CTAB/alkanols/cyclohexane system (alkanols: 1-butanol and 1-hexanol). The reaction can be considered to occur in the water phase of the droplets and from the rate constant the apparent dielectric constant of the water phase was determined. The cyclohexane incorporation in the system produces a decrease in the effective dielectric constant of the water phase and in the specific conductivity.     

Dielectric imaging of biological cells

A dielectric technique that can image local permittivity and conductivity has been applied to living biological cells in an aqueous environment. The local permittivity and conductivity were measured between 10 kHz and 10 MHz with a fine probe electrode, which was laterally scanned over cells on a plate electrode. The dielectric images of the cells depended on frequency, indicating dielectric relaxation that is due to interfacial polarization. The low-frequency image (at 10 KHz) in which the cells have high permittivity and low conductivity compared with the medium results from the presence of the plasma membrane with high resistivity. The dielectric image of the cell interior is obtainable at high frequencies (10 MHz), where the plasma membrane is short-circuited.     

The origin of DC electrical conduction and dielectric relaxation in pristine and doped poly(3‐hexylthiophene) films

We present here the evidence for the origin of dc electrical conduction and dielectric relaxation in pristine and doped poly(3‐hexylthiophene) (P3HT) films. P3HT has been synthesized and purified to obtain pristine P3HT polymer films. P3HT films are chemically doped to make conducting P3HT films with different conductivity level. Temperature (77–350 K) dependent dc conductivity (σ_dc) and dielectric constant (ε′(ω)) measurements on pristine and doped P3HT films have been conducted to evaluate dc and ac electrical conduction parameters. The relaxation frequency (f_R) and static dielectric constant (ε₀) have been estimated from dielectric constant measurements. A correlation between dc electrical conduction and dielectric relaxation data indicates that both dc and ac electrical conductions originate from the same hopping process in this system. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 1047–1053, 2010     

Dielectric relaxation of Tripropylene glycol–water mixture using time domain reflectometry

The complex permittivity spectra of tripropylene glycol and water solutions have been obtained by time domain reflectometry (TDR) technique in the frequency range from 10 MHz to 30 GHz and the temperature range 20°C–05°C. The dielectric relaxation parameters such as static dielectric constant and relaxation time were obtained by using the non-linear least square fit method. The intermolecular hydrogen bonding of tripropylene glycol–water has been discussed using the Kirkwood correlation factor and thermodynamic parameters. The activation energy decreases with increase in water content in the mixture as expected in the Arrhenius behaviour. The dielectric constant for mixtures has been fitted to the Bruggeman mixture formula in the non-linear case.     

Solution Properties of NaHSO4 and Na2SO4: A New Sight from the Water–Ion and Water–Dipole Cooperative Interactions Using Dielectric Relaxation Spectroscopy

The aqueous NaHSO₄ and Na₂SO₄ solutions at concentrations of 0.1–1.0 mol/l in a limited frequency range 0.2–20 GHz are studied by dielectric relaxation spectroscopy with a newly developed fractal concept spectral function. The fractal analysis with α(lnτ) diagrams from dielectric relaxation spectroscopy as functions proposed a new strategy to shed light on the dual nature of ion–water and dipole–water cooperative interactions. A distinct cooperative interaction of ion–water and dipole–water is observed and water molecules perturbed by ions contributing to dielectric constant beyond the first hydration shell is obtained.     

Hydration Dynamics of Water near an Amphiphilic Model Peptide at Low Hydration Levels: A Dielectric Relaxation Study

A dielectric relaxation study of aqueous solutions of the amphiphilic model peptide N‐acetyl‐leucine amide (NALA) at 298 K over a wide range of hydration levels is presented. The experiments range from states where water builds up several hydration layers to states where single water molecules or small water clusters are shared by several NALA molecules. The dielectric spectra reveal two modes on the 10 and 100 ps timescales. These are largely broadened with regard to the Lorentzian shape caused by simple Debye‐type relaxation, and are well described by the Kohlrausch–Williams–Watts stretched exponential function. The fast mode is assigned to water reorientation comprising bulk water as well as hydration water. Even when all water molecules are in contact with the solute, this fast component is dominant, and its mean relaxation time is retarded by less than a factor of two relative to neat water. The amplitude of the slow process is far higher than expected for the dipolar reorientation of the solute. The observations are consistent with results from molecular dynamics simulations for a similar model peptide reported in the literature. They suggest that the slow relaxation mode is mainly founded in peptide–water dipolar couplings, with some additional contribution from slowly reorienting hydration water molecules. The results are discussed with regard to the hydration dynamics of proteins and the interpretation of dielectric spectra of protein solutions.     

Limiting equivalent electrical conductivity of inorganic salt solutions and dielectric properties of a polar solvent

A relation has been found to exist between the limiting equivalent electrical conductivity of inorganic salt solutions, viscosity, temperature, and dielectric properties of the solvent. As temperature rises, the limiting equivalent electrical conductivity of aqueous solution of an inorganic salt has been shown to increase in direct proportion to the ratio of the dielectric permittivity to the dipole dielectric relaxation time, i.e., the limiting high-frequency electrical conductivity of the polar solvent. Expressions have been derived to be used in ascertaining the limiting equivalent electrical conductivities of inorganic salt solutions proceeding from the dielectric properties of the solvent.     

Dielectric relaxation behavior of ternary systems of water/toluene/Triton X-100: the effects of water and oil contents on microemulsion structure

Dielectric relaxation studies were conducted on the ternary systems of the nonionic surfactant Triton X-100 (a nonionic surfactant with a polyoxyethylene chain)/toluene/water in the frequency range from 40 Hz to 110 MHz. The contents of water and toluene were varied separately while the ratios of the other two components were fixed. Remarkable dielectric relaxations were observed around 1 MHz and dielectric intensity shows different variation with the increase of the contents of water or toluene. Dielectric parameters were obtained by fitting the data using the Cole–Cole equation with one dispersion term. The reverse micelles, water-in-oil, and oil-in-water micro-regions of the microemulsions were identified by the dependence of conductivity of the dispersed phase and continuous phase on the contents of water or toluene. Hanai theory and the corresponding analysis method were used to calculate the phase parameters of the constituent phases. The analysis results suggest that the dielectric relaxation probably arises from the interfacial polarization.