Dielectric Relaxation Of Water Research Articles

Dielectric relaxation in water of the adsorption layer on the surface of a solid

The influence of temperature and interphase boundary energy on the dielectric relaxation parameters in adsorbed water was investigated within the framework of thermodynamic consideration. It is shown that accounting for the interfacial boundary energy greatly increases the orientation dielectric relaxation time in adsorbed water. This allows us to determine the dispersion of the dielectric characteristics of adsorbed water using Debye’s relaxation theory.

Dielectric relaxation of water: assessing the impact of localized modes, translational diffusion, and collective dynamics.

A multitude of distinct physical processes and molecular mechanisms have been introduced in the past in an effort to understand the unusual dielectric loss spectrum of water with its pronounced peak at roughly 20 GHz. Our computer simulations including ab initio molecular dynamics provide no evidence for a major impact of cage dynamics or local-diffusive motion on the lineshape below 200 GHz. We also show that the collective motion of hundreds of water molecules and/or their significant diffusive displacements are not required. Instead, the dielectric relaxation of water up to about 200 GHz can be quantitatively described in terms of two unimodal and smoothly decaying spectral contributions.

The mechanism of the dielectric relaxation in water.

Although relating to the same system, the interpretations of the water spectra from Raman and Dielectric spectroscopy present independent pictures of the nature of water. We show that in the overlap region of the two methods it is possible to combine these views into a coherent concept of what drives the dynamic features of water. In this work, we develop the idea that the dielectric relaxation in water is driven by the migration of defects through the H-bond network, leading to a Debye-like peak in the lower frequencies. The deviation from the Debye law in the higher sub-THz frequencies is traced to a global fluctuation of the same H-bond network, clearly evident in the Raman Spectra. By incorporating these two views, a mathematical formalism is presented that can aptly explicate the dielectric spectra of liquid water.

Broadband complex dielectric constants of water and sodium chloride aqueous solutions with different DC conductivities

Broadband dielectric constant measurements in the frequency range between 40 Hz and 50 GHz of pure water, tap water, and sodium chloride aqueous solutions with different DC conductivities up to 5 S/m were conducted. The measurements were done using an impedance analyzer for the frequency range 40 Hz to 110 MHz and a vector network analyzer for 10 MHz to 50 GHz. The results show that the dielectric constant decreases with the increase in DC conductivity and is dependent on the frequency. The dielectric relaxation of water with a constant dielectric loss peak was also observed. The frequency dependence of the conductivity is also large. © 2014 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.

Relaxation dynamics in lens crystallin proteins: a dielectric and thermodynamic approach using TDR

Dielectric relaxation of water in biological systems, such as proteins and DNA, can often be described by two different time constants, one in the picosecond and the other in the nanosecond regime. In the present work, we report the temperature dependence of the relaxation dynamics, dielectric permittivity (e′) and loss (e′′) of aqueous lens proteins (crystalline) in the goat eye lens. The measurements have been carried out in the frequency range from 10 MHz to 20 GHz using TDR and in the temperature region from 298.15 K to 278.15 K. We analyse the three dispersion regions commonly found in protein solutions, usually termed β-, γ- and δ-relaxation. The β-relaxation, occurring in the frequency range between 70 and 100 MHz, and the γ-relaxation between 15 and 18 GHz can be attributed to the rotation of the polar protein molecules in their aqueous medium and the reorientational motion of the free water molecules respectively. The nature of δ-relaxation, which is often ascribed to the motion of bound water molecules, is not yet fully understood. Here, we provide data on the temperature dependence of dielectric and thermodynamic parameters of all three detected processes, β-, γ- and δ-relaxation. We found significant temperature dependence of the dielectric and thermodynamic parameters of the aqueous proteins, indicating conformational changes.

Dielectric Relaxation of Water in Clay Minerals

AbstractThe study of confined water dynamics in clay minerals is a very important topic in aluminosilicate-surface chemistry. Aluminosilicates are among the most technologically versatile materials in industry today. Dielectric spectroscopy is a very useful method for investigating the structure and dynamics of water adsorbed on solid matrix surfaces and water in the vicinity of ions in solutions. Use of this method for the study of clay minerals has been underutilized to date, however. The main goal of the present research was to understand the relaxation mechanisms of water molecules interacting with different hydration centers in clay minerals, with a view to eventually control this interaction. Two types of natural layered aluminosilicates (clay minerals) — montmorillonite with exchangeable K+, Co2+, and Ni2+ cations and kaolinite with exchangeable K+ and Ba2+ cations — were examined by means of dielectric spectroscopy over wide ranges of temperature (from -121°C to +300°C) and frequency (1 Hz–1 MHz). An analysis of the experimental data is provided in terms of four distributed relaxation processes. The low-temperature relaxation was observed only in montmorillonites and could be subdivided into two processes, each related to a specific hydration center. The cooperative behavior of water at the interface was observed in the intermediate temperature region, together with a proton percolation. The dielectric properties of ice-like and confined water structures in the layered clay minerals were compared with the dielectric response observed in porous glasses. The spatial fractal dimensions of the porous aluminosilicates were calculated by two separate methods — from an analysis of the fractality found in photomicrographs and from the dielectric response.

High Frequency Approaches for LTCC Based Sensors

Low temperature co-fired ceramics (LTCC) have been developed for RF and microwave circuits for a number of applications (i.e. cell phones and wireless systems). The same attributes that make LTCC an important technology for telecommunications are also important for sensors. Compact three-dimensional architectures with low dielectric loss materials are available with LTCC technology. The underlying electric and magnetic responses of materials in the RF and microwave frequency ranges will be discussed and these unique responses can be exploited in a sensor system. Gases, liquids and solids have unique dipolar responses in the RF and microwave ranges. For example, the dielectric relaxation of water has been investigated in water/starch mixtures. Classic dipolar relaxation of water occurs at 30GHz and additional relaxation mechanisms have been found in the 1–10 GHz range because of the starch gelation process. These relaxations could be the basis for a sensor system to monitor the gelation of food starches. In addition, miniature coil assemblies for magnetic resonance imaging (MRI) systems with operation in the 300 MHz to 850 MHz range will be presented. These types of coils with additional passive components are envisioned in a LTCC-based circuit topology.

Temperature dependence of vibrational frequency fluctuation of N3− in D2O

We have studied the temperature dependence of the vibrational frequency fluctuation of the antisymmetric stretching mode of N(3) (-) in D(2)O by three-pulse infrared (IR) photon echo experiments. IR pump-probe measurements were also carried out to investigate the population relaxation and the orientational relaxation of the same band. It was found that the time-correlation function (TCF) of the frequency fluctuation of this mode is well described by a biexponential function with a quasistatic term. The faster decay component has a time constant of about 0.1 ps, and the slower component varies from 1.4 to 1.1 ps in the temperature range from 283 to 353 K. This result indicates that liquid dynamics related to the frequency fluctuation are not highly sensitive to temperature. We discuss the relationship between the temperature dependence of the vibrational frequency fluctuation and that of the molecular motion of the system to investigate the molecular origin of the frequency fluctuation of the solute. We compare the temperature dependence of the frequency fluctuation with that of other dynamics such as dielectric relaxation of water. In contrast to the Debye dielectric relaxation time of D(2)O, the two time constants of the TCF of the frequency fluctuation do not exhibit strong temperature dependence. We propose a simple theoretical model for the frequency fluctuation in solutions based on perturbation theory and the dipole-dipole interaction between the vibrational mode of the solute and the solvent molecules. This model suggests that the neighboring solvent molecules in the vicinity of the solute play an important role in the frequency fluctuation. We suggest that the picosecond component of the frequency fluctuation results from structural fluctuation of the hydrogen-bonding network in water.

Dielectric Relaxation of Water in Hydration Shells of Ions

Microwave spectroscopy has been used to study the dielectric properties of aqueous electrolyte solutions over a wide range of concentrations, the frequency range (7 to 25 or 7 to 120) GHz, and the temperature range (283 to 313 or 288 to 308) K. The static dielectric permittivity, dielectric relaxation time, and activation enthalpy have been calculated for 46 binary systems. General relations between dielectric relaxation parameters and structural effects in aqueous salt solutions are considered. The increase in the order of complementary structural organization for water in the bulk and hydration shells of ions gives rise to the molecular-kinetic stabilization of water and to the structure-making effect. This explains the difference between dielectric relaxation characteristics for a wide variety of electrolyte solutions. We present systematic dielectric data for aqueous electrolytes with hydrophilic and hydrophobic hydration of cations and anions. The temperature effect is also examined. On the basis of ...

Dielectric secondary relaxation of water in aqueous binary glass-formers

Glassy aqueous binary mixtures generally exhibit a water induced dielectric relaxation. The characteristic time-scale of this relaxation follows an Arrhenius temperature dependence with a nearly universal activation energy. We here demonstrate for a series of model aqueous mixtures that the relaxation time also follows a remarkably general exponential dependence on the weight fraction of water. By comparison to literature data we show that this behaviour is shared by a wide range of molecular systems. Neither the detailed nature of the water molecules' glassy environment nor the details of the route of formation of the glassy state has a significant effect on the observed behaviour.

Dielectric relaxation of water adsorbed on wood and charcoal

Abstract The dielectric relaxation due to motions of water molecules adsorbed on wood treated at various temperatures up to 550°C was investigated based on the relationships between activation enthalpy (ΔH) and entropy (ΔS) in relaxation. The relationships indicated two straight lines with different slopes, depending on the treatment temperature. Given the same ΔS, ΔH values for water molecules adsorbed on wood treated at temperatures below 400°C were greater than for those treated above 450°C. It was considered that before heat treatment, water molecules were adsorbed mainly on hydroxyl groups by strong hydrogen bonds and formed ice-like structures. On the other hand, hydroxyl groups were not detected in wood after heat treatments above 400°C. We assume that water molecules are condensed in nanometer-scale micropores that are formed during the carbonization of wood. The relationship between ΔH and ΔS for the motion of water adsorbed on wood treated above 450°C was similar to the value extrapolated from that for bulk water at temperatures below 0°C. We suggest that water molecules are adsorbed on charcoal in a supercooled state.

Dielectric relaxation of water adsorbed on chemically treated woods

Abstract Changes in the dielectric relaxation due to water adsorbed on eight types of chemically treated woods, as well as untreated wood (Picea sitchensis Carr.), with moisture content (MC) were investigated in the temperature range between −150°C and 20°C and in the frequency range between 100 Hz and 1 MHz. Cole-Cole's circular arc law was applied to the results of dielectric measurements conducted at seven levels of relative humidity (RH), and the relaxation spectra at −75°C were calculated. The theory of rate processes was applied to the dielectric relaxation resulting from the motions of water molecules adsorbed on the untreated and chemically treated woods, and the binding state of adsorbed water was examined. The relaxation magnitude increased with increasing MC, irrespective of the chemical treatment. The distribution of relaxation times decreased in the MC range below 1%, but increased with increasing MC at higher levels. The generalized relaxation time increased up to 5% MC, then decreased. The enthalpy-entropy compensation phenomenon was observed in the dielectric relaxation, which was derived from the adsorption of water molecules on the chemically treated woods. The binding states of adsorbed water and ice were similar. The water molecules adsorbed on wood may have produced a very wide variety of cohesive structures in the chemically treated woods.

Dielectric relaxation in water–cholesterol mixture cluster: molecular dynamics simulation

Molecular dynamics (MD) studies of the cluster composed of cholesterol (C27H45OH) and water molecules are presented. We have investigated several dynamical quantities of cholesterol as a function of its concentration in the mixture cluster and the temperature. The main attention was focused on the temperature and concentration dependence of the calculated total dipole moment autocorrelation function and dielectric loss of the cluster.

Dielectric Relaxation Based on Adsorbed Water in Wood Cell Wall under Non-Equilibrium State. Part 3. Desorption

Summary The temperature and frequency spectra of dielectric constant ε′ and dielectric loss factor ε″ of Sikkim spruce (Picea spinulosa Griff.) were measured to investigate the change in dielectric relaxation of water in wood during desorption. In order to control the rate of moisture content change, the measurements were carried out in three steps: from fiber saturation point to 80% RH, from 80% RH to 60% RH and from 60% RH to 20% RH, at 25°C. Two dielectric relaxation processes were observed in different temperature and frequency regions which changed their position and strength with the desorption process. Using the ε′ and ε″ spectra, two groups of Cole-Cole plots were obtained, on which basis two groups of dielectric parameters including the static dielectric constant εS, optic dielectric constant ε∞, relaxation strength (εS–ε∞), and the relaxation time distribution coefficient α were calculated. Both groups of parameters showed similar trends, that is, ε∞ remained nearly constant during the whole desorption process. εS and (εS–ε∞)changed little during the first step of desorption, decreased obviously during the second step and declined slightly during the third step. The α value obtained from the lower frequency data changed significantly during the second and third desorption steps, while there was little change in the other group of α values. These differences can be explained by different mechanisms of the relaxation processes in the lower and higher frequency regions.

Translational diffusion and reorientational relaxation of water analyzed by site–site generalized Langevin theory

The translational and rotational diffusion coefficients and the dielectric spectrum of water at the ambient condition are calculated using the exponential memory model previously proposed by us. The translational diffusion coefficient is in good agreement with experiments and computer simulations. However, the rotational diffusion and dielectric relaxation of the present theory are about ten times as fast as those of experiments. In order to clarify the origin of the disagreement, the memory kernel is directly obtained from the molecular-dynamics simulation and compared with the exponential model. It is found that the long-time part of the memory kernel, which is not considered in the exponential model, is dominant in the rotational diffusion and the dielectric relaxation of water.

Dielectric relaxation measurements onmethanol up to the supercritical region

The static permittivity ε(0) and the dielectricrelaxation time τD have been obtained for methanol over a widerange of temperature and pressure up to 600 K and 21 MPa. Thedielectric relaxation time τD decreases with increasingtemperature and has little pressure dependence in the liquid state.In the gaseous state, however, τD increases with decreasingdensity. Since these behaviours are qualitatively the same as thosefor water, we have successfully applied our model for the dielectricrelaxation in water to that in methanol with some appropriatemodifications.

Dielectric relaxation of water and water-plasticized biomolecules in relation to cellular water organization, cytoplasmic viscosity, and desiccation tolerance in recalcitrant seed tissues.

To understand the relationship between the organization of cellular water, molecular interactions, and desiccation tolerance, dielectric behaviors of water and water-plasticized biomolecules in red oak (Quercus rubra) seeds were studied during dehydration. The thermally stimulated current study showed three dielectric dispersions: (a) the relaxation of loosely-bound water and small polar groups, (b) the relaxation of tightly-bound water, carbohydrate chains, large polar groups of macromolecules, and (c) the "freezing in" of molecular mobility (glassy state). Seven discrete hydration levels (water contents of 1.40, 0.55, 0.41, 0.31, 0.21, 0.13, and 0.08 g/g dry weight, corresponding to -1.5, -8, -11, -14, -24, -74, and -195 MPa, respectively) were identified according to the changes in thermodynamic and dielectric properties of water and water-plasticized biomolecules during dehydration. The implications of intracellular water organization for desiccation tolerance were discussed. Cytoplasmic viscosity increased exponentially at water content < 0.40 g/g dry weight, which was correlated with the great relaxation slowdown of water-plasticized biomolecules, supporting a role for viscosity in metabolic shutdown during dehydration.

The dielectric relaxation of water between 0°C and 35°C

Precise complex permittivity data from our laboratory for pure water at temperatures 0.2⩽ ϑ/°C⩽35 are combined with literature results to cover the frequency range 0.2⩽ ν/GHz⩽410. A description of the ε ̂ (ν) spectra requires the superposition of two Debye processes. Nonetheless, relaxation times and dispersion amplitudes discourage the discussion of the water structure in terms of a two-state model. The interpretation of the fast process with the relaxation time τ 2 requires additional information, whereas it is possible to relate the relaxation time τ 1 of the dominating slow process to the production rate of mobile water molecules. From the corresponding Eyring free energy, Δ G ≠, hydrogen-bond probabilities are deduced, which are in good agreement with data from other methods.

Dielectric relaxation of water and heavy water in the whole fluid phase

Recently we developed a new microwave spectroscopy technique in the frequency range up to 40 GHz, and measured the static dielectric constant and the dielectric relaxation time for supercritical water. In the present work we report the dielectric properties of heavy water at temperatures and pressures up to 770 K and 59 MPa, respectively. The static dielectric constant of D2O as well as H2O are well described by the Uematsu–Franck formula when the number density instead of the mass density is used as the input parameter. The dielectric relaxation time decreases rapidly with increasing temperature in liquid H2O and D2O and jumps to a large value at the liquid–gas transition. The relaxation time of D2O is longer than that of H2O in the liquid state, and the difference becomes smaller with decreasing density in the gaseous state. For both H2O and D2O the most relevant parameter determining the relaxation time is the temperature at high densities or at low temperatures, and it is the density at low densities or at high temperatures. Based upon the observation that the dielectric relaxation time becomes fairly long in the dilute limit, we have concluded that the dielectric relaxation in the gaseous state is governed by the binary collision of water molecules and explained the relaxation time quantitatively by the collision time. We have extended the interpretation of the dielectric relaxation to the liquid state by taking into account the contribution of bound water molecules that are incorporated in the hydrogen-bond network. Anomalous relaxation at low temperatures is also discussed.

Dielectric Relaxation in Supercritical Water.

The dielectric relaxation in water and heavy water have been measured in the temperature and pressure ranges up to 750°C and 120 MPa by using a newly developed microwave spectroscopy in the frequency range up to 40 GHz. The dielectric relaxation time τ is deduced from observed transmission spectrum on the assumption that the dielectric constant obeys the Debye relaxation. Below about 350°C τ rapidly decreases with increasing temperature irrespective of pressure, while at higher temperatures r changes little with temperature and increases rapidly with decreasing density.