Dielectric Relaxation Of Water Research Articles

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.

Microwave spectroscopy of supercritical water

Microwave spectroscopy that can be applied to study the dielectric relaxation of various fluids under high temperature and pressure has been developed in the frequency range up to 40 GHz. By utilizing this new technique, the dielectric relaxation of water has been measured in the temperature and pressure range up to 750 °C and 120 MPa, which corresponds to a density range between 0.05 and 1 g/cm3. The static dielectric constant ε(0) is deduced from the time required for a microwave signal to travel through the sample by means of the time domain analysis, and is in good agreement with the literature. The dielectric relaxation time τ is obtained by fitting the experimentally observed microwave transmission rate to the value calculated using the S-matrices on the assumption that the dielectric constant obeys the Debye relaxation. The results of τ at ambient pressure agree very well with previous data. Below about 350 °C, τ rapidly decreases with increasing temperature nearly independent of pressure, while above about 350 °C, τ changes little with temperature and increases rapidly with decreasing density. It is concluded that the most relevant parameter determining τ is the temperature at lower temperatures or higher densities, and it is the density d at higher temperatures or lower densities. A possible change in the nature of hydrogen bonding is suggested to explain the observed temperature and density dependence of τ.

超臨界水の誘電緩和測定

Microwave spectroscopy that can be applied to study the dielectric relaxation of various fluids under high temperature and pressure has been developed in the frequency range up to 40 GHz. By utilizing this new technique the dielectric relaxation in water has been measured in the temperature and pressure range up to 750°C and 120 MPa, which corresponds to a density range between 0. 05 and 1 g/cm3. The static dielectric constant e (0) is deduced from the time required for microwave signal to travel through the sample by means of the time domain analysis. The dielectric relaxation time τ is obtained by fitting the experimentally observed microwave transmission rate to the value calculated using the Smatrices on the assumption that the dielectric constant obeys the Debye relaxation. It is concluded that the most relevant parameter determining τ is the temperature at lower temperatures or higher densities, and is the density at higher temperatures or lower densities.

Study of aggregation in water— n-butoxyethanol solutions by dielectric relaxation measurements

The dielectric relaxation of water— n-butoxyethanol mixtures has been studied as a function of alcohol concentration in the water-rich region by means of a frequency domain coaxial technique in the range 10 MHz—3 GHz. Both the static dielectric constant and dielectric relaxation time exhibit an anomalous behaviour which further supports the existence of a butoxyethanol microphase above a critical concentration (mole fraction of cosolvent X*=0.026 at T=2°C). Experimental data have been analyzed in terms of a simple model in which water molecules are divided in two main groups, hydration and bulk water, mutually exchanging at a finite rate.

The Dielectric Relaxation of Water in Plant Tissue

Thermally stimulated depolarization current (TSDC) measurements on plant leaves and stems of six different species in the temperature range of 77-300 K revealed the existence of three different dispersions. The first dispersion at low temperatures, which is attributed to the relaxation of loosely bound water molecules was studied in detail in an attempt to obtain information on the possible structures of water in plant tissue. Its characteristics differ for various plant tissues, indicating a different organization of water in those plant tissues. The dispersion can be described by a continuous distribution of relaxation times r with both the activation energy W and the pre-exponential factor t0 in the Arrhenius equation being distributed parameters. The spectrum of W and r0 was determined for E. globulus and O. europaea leaf samples. The mean values of r and W are larger and that of t0 smaller than the corresponding values for free (bulk) water. The results favour a model of the organization of water in clusters rather than in multilayers and indicate a stronger binding of water in living systems.

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.

Dielectric relaxation in water. Computer simulations with the TIP4P potential

In this second paper in a series of systematic investigations seeking to relate the dielectric properties of water to the features of the intermolecular potential, extensive molecular dynamics simulations with the empirical TIP4P effective pair potential are compared with the experimental data for water as well as with the results reported previously for the MCY ab initio model. The frequency dependence of the dielectric constant obtained for the two models is contrasted with the predictions of a Mori three-variable theory and analyzed in detail using a phenomenological description of dielectric relaxation. It is shown that both models are capable of reproducing all reorientational processes observed in the experimental spectrum. However, qualitative agreement with the experimental results for the Debye relaxation time and the static Kirkwood g-factor gK is only obtained with the TIP4P model, although the values are still too low and ∂gK/∂T has the wrong sign. The differences between the models are interpreted as being due to the different position chosen for the center of negative charge, and it is argued that moving the latter further towards the oxygen would, for simple rigid point charge models, yield considerably improved agreement with experiment.

Thermal properties of water in myoglobin crystals and solutions at subzero temperatures

The water of hydration in myoglobin crystals and solutions was studied at subzero temperatures by calorimetry and infrared spectroscopy (ir). For comparison we also investigated glycine, DL-alanine and DL-valine solutions. The hydration water remains amorphous at low temperatures. We find a broad glass transition between 180 and 270 K depending on the degree of hydration. The ice component shows a noncolligative melting point depression that is attributed to a finite conformational flexibility. The ir spectrum and the specific heat of water in myoglobin crystals was determined for the first time between 180 and 290 K. The glass transition in crystals is qualitatively similar to what is found in amorphous samples at the same water content. These data are compared with Mössbauer experiments and dielectric relaxation of water in myoglobin crystals. The similar temperature dependencies suggest a cross correlation between structural fluctuations and the thermal motion of crystal water. A hydrogen bond network model is proposed to explain these features. The essential ingredients are cooperativity and a distribution of hydrogen-bonded clusters.

Microwave dielectric relaxation of water in hydrated melts: system Ca(NO3)2.4H2O

The microwave complex permittivities of hydrated melts of composition Ca(NO3)2 3.9 H2O, in the frequency range 8.2–79 GHz, and temperature range 40–55°C, are reported. The real and imaginarry coefficients of the complex permittivity show a dielectric relaxation process, which can be described in most of the frequency range by a Debye function for a single relaxation. Some deviation becomes apparent, however, at the upper end of the frequency range investigated. Eyring plots of the inverse of the relaxation time vs the inverse of temperature give the activation parameters for the process. The latter is interpreted as due to the rotation of water in the melts, all the water being probably coordinated with the cations. Compared to the activation parameters in pure water one notices an increase in both the enthalpy and entropy of activation. An increase in the activation energy in concentrated aqueous LiCl has been already reported in the literature.

Dielectric Relaxation of Water Contained in Plant Tissues

Low frequency dielectric relaxation has been observed in the water contained in plant seeds, woody parts of trees and leaves of evergreen trees, but it has not been observed in the water contained in grass stems and leaves of deciduous trees. From an empirical relation obtained, these results indicate that OH groups which act as active centres for the adsorption of water exist in the plant tissues of the former group but not in those of the latter group. The activation energy necessary for the dipole orientation of the water molecules in most plant tissues is of the order of 0.5–0.6 eV.

Dielectric Relaxation of Water in Aqueous Solutions of n‐Alkylamine Hydrochlorides Part 2: Solute Concentrations Larger than the Critical Micelle Concentrations

AbstractThe solutes are the chlorides of the amphiphilic cations CH3(CH2)n N+ H3 with n = 5, 6, 7, 9 and CH3(CH2)11 N+(CH3)3, which above the critical micelle concentration aggregate to micelles in aqueous solutions. The complex permittivity of the solutions has been measured in dependence of frequency between 5 and 37 GHz at 25°C.From the analysis of the frequency dependence of the complex permittivity, statements are made on the micellar shape and on the microdynamics of the water molecules influenced by the micelles.The micellar shape seems to be ellipsoidal within the high concentrated solutions. There are two species of micellar hydration water. One species is characterized by a very large reorientation time of the molecules. This effect is attributed to the pourous structure of the micellar surface. The reorientation time of the other species is somewhat smaller than the reorientation time of pure water. This is explained by weak electric fields acting near the micellar surface and thus causing negative hydration.

Dielectric Relaxation of Water in Aqueous Solutions of n‐Alkylamine Hydrochlorides Part 1: Solute Concentrations Smaller than the Critical Micelle Concentrations

AbstractThe solutes are the homologous salts CH3(CH2)nNH3Cl with n = 3, 5, 6, and 7. The complex permittivity of the solutions has been measured in dependence of frequency between 5 and 37 GHz at 25°C.From the analysis of the frequency dependence of the complex permittivity, statements are made on the orientational polarizability, the reorientation time and the number of the hydration water molecules of the n‐alkylammonium ions. The orientational polarizability of the hydration water does not markedly differ from that of pure water. The reorientation time and the numbers of the disturbed water molecules around the cations strongly increase with increasing hydrocarbon chain length of the cations.The reorientation times and the numbers of the hydration water molecules of the n‐alkylammonium ions are compared with those of the tetra‐alkylammonium ions. From this comparison is clearly established that the hydrophobic interaction around the former ions is more pronounced than around the latter.

Dielectric relaxation in water in the neighborhood of 4°C

The complex permittivity of water has been measured at seven temperatures between 3 and 5°C over a frequency range of 0.4–4 GHz. The data are analyzed first in terms of a small but significant distribution of relaxation times of magnitude larger than that observed previously and then as two separate Debye process having relaxation times separated by a factor of ∼2. It is shown that one possible interpretation of these observations is that a bond breaking process takes place in which the rate of formation of one bonded molecules from two bonded molecules depends upon whether the latter are bonded symmetrically or unsymmetrically. The value of the high frequency permittivity (ε∞) calculated from this model is shown to agree well with experiment. There is no evidence of any abrupt changes (``kinks'') greater than random experimental error in the temperature variation of the dielectric parameters of water between 3–5°C.

Dielectric properties of the hydrates of argon and nitrogen

The dielectric relaxation of water in the structure I clathrate hydrates of argon and nitrogen was studied over a range of temperature and pressure. Hydrates were slowly grown at pressures of 1 to 2 kbar in a coaxial cell enclosed in a pressure vessel. The complex permittivity loci resemble circular arcs with static dielectric constants of ~56 at 0 °C and high-frequency dielectric constants of 2.85 ± 0.05. Relaxation near 0 °C is about as slow as in ice I, but activation energies and entropies are much smaller. Formation of Bjerrum defects probably takes place preferentially near the occasional sites at which argon and nitrogen molecules have replaced water molecules in the lattice. The much faster relaxations found previously in the isostructural hydrates of ethers arise from orientational defects induced in the water lattice by the encaged molecules, a small proportion of which may form hydrogen bonds with water. The effect of small gaps in series with samples showing circular-arc dispersion behavior was evaluated.

The mechanism of dielectric relaxation in water

The mechanism of dielectric relaxation in water

Dielectric relaxation in water adsorbed on alums

Dielectric relaxation in water adsorbed on alums

Dielectric relaxation in water adsorbed on ionic crystals

At 0·9 Mc./sec., dielectric loss in water adsorbed on CaF2, MgO, and KCl powders is observed when the coverage exceeds about 0·5. To some extent the isotherms at 0° for these adsorbents conform to the B.E.T. type II classification. With KCl, anomalous behaviour is attributed to surface dissolution during multilayer adsorption. A multilayer phase transition shown by peaks in the variation of loss with temperature is discussed. There is evidence to show that AgI may promote a more ordered multilayer structure. Dielectric loss generally increases with increasing frequency in the range investigated. The nature of the relaxation process is uncertain, although certain features can be interpreted qualitatively in terms of a Maxwell–Wagner mechanisms.

SOME OBSERVATIONS ON THE THEORY OF DIELECTRIC RELAXATION IN ASSOCIATED LIQUIDS

The theory of absolute reaction rates is examined for the case of relaxation in associated polar liquids where the activation process is probably an excitation of a librational motion to one of complete rotation over a rotational potential energy barrier. The rotational barriers in water are calculated using the point-charge model of the water quadrupole and the effect of thermal bond bending is examined. The experimental heats of activation for dielectric relaxation in water and deuterium oxide are discussed and their temperature dependence examined; the heat capacity change for rotational activation is derived. Isotopic effects in the heats of activation, the relaxation times, and frequency factors are discussed. A qualitative explanation is sought for the homogeneity of relaxation times in water; rotation of water molecules in the fields of the hydroxonium and hydroxide ions present in water may account for the narrow distribution of relaxation times observed experimentally. This mechanism is shown to be consistent with other theoretically derived quantities and with the mechanism of proton mobility in water. A different mechanism is indicated in ice, where the proton concentration is lower, but in ice containing extra protons, the mechanism probably reverts to that existing in water.