Static Dielectric Constant Of Water Research Articles

Temperature-Dependent Dielectric Relaxation Measurements of (Betaine + Urea + Water) Deep Eutectic Solvent in Hz-GHz Frequency Window: Microscopic Insights into Constituent Contributions and Relaxation Mechanisms.

A combined experimental and simulation study of dielectric relaxation (DR) of a deep eutectic solvent (DES) composed of betaine, urea, and water with the composition [Betaine:Urea:Water = 11.7:12:1 (weight ratio) and 9:18:5 (molar ratio)] was performed to explore and understand the interaction and dynamics of this system. Temperature-dependent (303 ≤ T/K ≤ 343) measurements were performed over 9 decades of frequency, combining three different measurement setups. Measured DR, comprising four distinct steps with relaxation times spreading over a few picoseconds to several nanoseconds, was found to agree well with simulations. The simulated total DR spectra, upon dissection into three self (intraspecies) and three cross (interspecies) interaction contributions, revealed that the betaine-betaine self-term dominated (∼65%) the relaxation, while the urea-urea and water-water interactions contributed only ∼7% and ∼1%, respectively. The cross-terms (betaine-urea, betaine-water, and urea-water) together accounted for <30% of the total DR. The slowest DR component with a time constant of ∼1-10 ns derived dominant contribution from betaine-betaine interactions, where betaine-water and urea-water interactions also contributed. The subnanosecond (0.1-0.6 ns) time scale originated from all interactions except betaine-water interaction. An extensive interaction of water with betaine and urea severely reduced the average number of water-water H-bonds (∼0.7) and heavily decreased the static dielectric constant of water in this DES (εs ∼ 2). Furthermore, simulated first rank collective single particle reorientational relaxations (C1(t)) and the structural H-bond fluctuation dynamics (CHB (t)) exhibited multiexponential kinetics with time scales that corresponded well with those found both in the simulated and measured DR.

Comprehensive quantum calculation of the first dielectric virial coefficient of water.

We present a complete calculation, fully accounting for quantum effects and for molecular flexibility, of the first dielectric virial coefficient of water and its isotopologues. The contribution of the electronic polarizability is computed from a state-of-the-art intramolecular potential and polarizability surface from the literature, and its small temperature dependence is quantified. The dipolar polarizability is calculated in a similar manner with an accurate literature dipole-moment surface; it differs from the classical result both due to the different molecular geometries sampled at different temperatures and due to the quantization of rotation. We calculate the dipolar contribution independently from spectroscopic information in the HITRAN2020 database and find that the two methods yield consistent results. The resulting first dielectric virial coefficient provides a complete description of the dielectric constant at low density that can be used in humidity metrology and as a boundary condition for new formulations for the static dielectric constant of water and heavy water.

Tuning the Dielectric Response of Water in Nanoconfinement through Surface Wettability.

The tunable polarity of water can be exploited in emerging technologies including catalysis, gas storage, and green chemistry. Recent experimental and theoretical studies have shown that water can be rendered into an effectively apolar solvent under nanoconfinement. We furthermore demonstrate, through molecular simulations, that the static dielectric constant of water can be modified by changing the wettability of the confining material. We find the out-of-plane dielectric response to be highly sensitive to the level of confinement and can be reduced up to 40× , in accordance with experimental data. By altering the surface wettability from superhydrophilic to superhydrophobic, we observe a 36% increase for the out-of-plane and a 31% decrease for the in-plane dielectric constants. Our findings demonstrate the feasibility of tunable water polarity, a phenomenon with great potential for scientific and technological impact.

Dielectric constant of supercritical water in a large pressure-temperature range.

A huge amount of water at supercritical conditions exists in Earth's interior, where its dielectric properties play a critical role in determining how it stores and transports materials. However, it is very challenging to obtain the static dielectric constant of water, ϵ0, in a wide pressure-temperature (P-T) range as found in deep Earth either experimentally or by first-principles simulations. Here, we introduce a neural network dipole model, which, combined with molecular dynamics, can be used to compute P-T dependent dielectric properties of water as accurately as first-principles methods but much more efficiently. We found that ϵ0 may vary by one order of magnitude in Earth's upper mantle, suggesting that the solvation properties of water change dramatically at different depths. Although ϵ0 and the molecular dipole moment increase with an increase in pressure along an isotherm, the dipolar angular correlation has its maximum at 5 GPa-7 GPa, which may indicate that hydrogen bonds become weaker at high pressure. We also calculated the frequency-dependent dielectric constant of water in the microwave range, which, to the best of our knowledge, has not been calculated from first principles, and found that temperature affects the dielectric absorption more than pressure. Our results are of great use in many areas, e.g., modeling water-rock interactions in geochemistry. The computational approach introduced here can be readily applied to other molecular fluids.

Altered polar character of nanoconfined liquid water

Dielectric properties of nanoconfined water are investigated by theory and computer simulations. The authors observe a dependence of the effective static dielectric constant of water with the confinement while the total dipole moment relaxation appears largely independent of it. These anomalous properties are explained in terms of a destructive interference of inwardly propagating surface induced long range correlations.

Screening of an Electric Field in Water

The screening of an electric field in water has been studied taking into account correlations between protons, which are described by the ice rules. It is shown that the problem has two characteristic screening lengths l1 ≪ l2, which are determined by majority and minority charge carriers in water. The commonly accepted static dielectric constant of water about 83 at room temperature is applicable only in the distance range l1 ≪ x ≪ l2. At smaller distances, the dielectric constant is determined by the high-frequency dielectric constant and is ϵ∞ ≈ 3.2, whereas the dielectric constant at large distances tends to infinity, which corresponds to the complete screening of the electric field. The screening lengths have been numerically determined, their temperature dependences have been described, and an experiment has been proposed to test the results obtained.

Static dielectric constant of water within a bilayer using recent water models: a molecular dynamics study

The water confined within a surfactant bilayer is studied using different water models via molecular dynamics simulations. We considered four representative rigid models of water: the SPC/E and the TIP4P/2005, which are commonly used in numerical calculations and the more recent TIP4Q and SPC/ε models, developed to reproduce the dielectric behaviour of pure water. The static dielectric constant of the confined water was analyzed as a function of the temperature for the four models. In all cases it decreases as the temperature increases. Additionally, the static dielectric constant of the bilayer-water system was estimated through its expression in terms of the fluctuations in the total dipole moment, usually applied for isotropic systems. The estimated dielectric was compared with the available experimental data. We found that the TIP4Q and the SPC/ε produce closer values to the experimental data than the other models, particularly at room temperature. It was found that the probability of finding the sodium ion close to the head of the surfactant decreases as the temperature increases, thus the head of the surfactant is more exposed to the interaction with water when the temperature is higher.

In situ Raman spectroscopy investigation of the solubility and dissolution mechanism of 1,2‐dichlorobenzene in hot compressed water in a fused silica capillary reactor

Hot compressed water (HCW), with its unique properties, is regarded as a promising solvent for industrial applications. A number of methods to measure the solubility of hydrophobic organic compounds (HOCs) in HCW have been reported. However, these methods were conducted in large‐scale stainless‐steel reactors, and few included an in situ study regarding the dissolution mechanism of HOCs in HCW during the solubility determination process. In this study, a fused silica capillary reactor in combination with Raman spectroscopy was applied to investigate phase changes, determine the solubility, and study the dissolution mechanism of 1,2‐dichlorobenzene in HCW. The total dissolution process of 1,2‐dichlorobenzene in HCW was observed under a microscope, and the images were recorded continuously using a digital camera. Raman spectroscopy was used to confirm the homogeneity of the 1,2‐dichlorobenzene solution during dissolution. The solubility of 1,2‐dichlorobenzene increased from 35.9 to 85.7 mg g−1 in water with increasing temperature from 256.7 to 294.1 °C. Furthermore, the dissolution mechanism of 1,2‐dichlorobenzene in HCW is proposed based on the Raman spectra of 1,2‐dichlorobenzene and water during the dissolution process in the fused silica capillary reactor. The breakage of the fully hydrogen‐bonded (tetrahedral) configuration and the consequent change in the static dielectric constant of water are deemed to be compelling reasons for the high solubility of 1,2‐dichlorobenzene in HCW. Our experimental method exhibits great potential for determining the solubility of HOCs in HCW and for investigating their dissolution behavior and dissolution mechanism at elevated pressure and temperature conditions. Copyright © 2017 John Wiley &amp; Sons, Ltd.

Spatially resolved dielectric constant of confined water and its connection to the non-local nature of bulk water.

We use molecular dynamics simulations to compute the spatially resolved static dielectric constant of water in cylindrical and spherical nanopores as occurring, e.g., in protein water pockets or carbon nanotubes. For this, we derive a linear-response formalism which correctly takes into account the dielectric boundary conditions in the considered geometries. We find that in cylindrical confinement, the axial component behaves similar as the local density akin to what is known near planar interfaces. The radial dielectric constant shows some oscillatory features when approaching the surface if their radius is larger than about 2 nm. Most importantly, however, the radial component exhibits pronounced oscillations at the center of the cavity. These surprising features are traced back quantitatively to the non-local dielectric nature of bulk water.

Note: Extraction of hydrogen bond thermodynamic properties of water from dielectric constant and relaxation time data

We recently proposed a theory [Suresh, J. Chem. Phys. 113, 9727 (2000)]10.1063/1.1320822, based on the principles of statistical mechanics, for describing the temperature variation of static dielectric constant of water and the average number of H-bonds per molecule in the liquid phase. The theoretical model contains three parameters; two of them pertain to the energy and entropy changes accompanying bond-formation, and the third (ε∞) represents the dielectric constant at a frequency that is sufficiently low for atomic and electronic polarization, but sufficiently high for intermolecular relaxation processes involving the movement of permanent dipole moments to be inoperative. In the absence of a consensus in the literature for the value of ε∞ to be used in dielectric constant calculations, it was arbitrarily set to a commonly accepted value of 1.77 (corresponding to refractive index of 1.33). Values for H-bond parameters were then estimated by best fitting model calculations to experimental data for dielectric constant across temperatures ranging from melting to the critical point of water. It is the purpose of the present Note to eliminate the ambiguity on the choice of ε∞ and propose refined values for the H-bond parameters.

On the temperature dependence of the primary yield and the product Gεmax of hydrated electrons in the low-LET radiolysis of liquid water

Monte-Carlo simulations are performed to calculate the temperature dependence of the primary hydrated electron yield (Geaq-) for liquid water irradiated by low linear-energy-transfer radiation (LET ~ 0.3 keV µm–1) in the range 25–325°C. Calculations are carried out by taking properly into account the effect of the time and temperature dependencies of the water dielectric constant on the electron–cation geminate recombination. Our computed Geaq- values slightly increase with increasing temperature, in good agreement with experiment. The product Geaq- εmax(eaq-), estimated by using existing experimental data of the maximum molar extinction coefficient εmax(eaq-), remains nearly constant or slightly increases, depending on the temperature dependence chosen for εmax. Our Geaq-εmax(eaq-) values compare generally well with most experimental data, as well as with the predictions of deterministic diffusion-kinetic model calculations. Moreover, our results indicate that the static dielectric constant of water (εs) does not play any significant role on the electron–cation recombination at early times. Such a finding is inconsistent with the interpretation, proposed by certain authors in the literature, that Geaq- should in fact decrease as temperature is increased because of an increased electron–cation geminate recombination due to a lowering of εs. Finally, the temperature dependence of the hydrated electron yields, calculated at various times between 10 ps and 1 µs, shows that at low LET, the time required to establish homogeneous chemistry in the bulk of the solution is ~10–6 s in the range ~25–100°C, and that this time diminishes to ~10–7 s at higher temperatures. Key words: liquid water, radiolysis, temperature, hydrated electron (eaq-), radiolytic yields, electron–cation geminate recombination, dielectric constant, molar extinction coefficient of eaq-, homogenization time.

Hydrogen bond thermodynamic properties of water from dielectric constant data

We apply statistical mechanical principles to derive simple expressions relating the hydrogen bond thermodynamic properties to the static dielectric constant of water. The approach followed by us was to develop an expression for the Kirkwood’s structure factor (g) of water, taking into account the dipolar correlations between a central molecule and H-bonded neighbors present in infinite number of shells surrounding the central molecule. The number of H-bonded neighbors in a specific shell was related to the probability P for the various donor/acceptor sites of any given water molecule to be associated. Neglecting cooperativity effects, we evaluated P by focusing only on the correct counting of H-bonds formed between various association sites rather than on the oligomer distribution. The theory yielded an extremely simple expression for the structure factor (g) of the fluid at any given temperature in terms of the enthalpy (H) and entropy (S) changes associated with bond formation. The proposed theory was then combined with the Kirkwood–Frohlich theory for evaluating the dielectric constant (ε0). We have demonstrated that the theory correctly predicts the dielectric constant of ice-I without the use of any adjustable parameters. We have then deduced estimates for H-bond thermodynamic properties (H=−5.58 kcal/mole of H-bonds; S=−8.89 cal/deg⋅mole of H-bonds) by fitting the theoretical results for ε0 of liquid water to available experimental data over temperatures ranging from 0 °C to the critical point of water. The error in the theoretical values was found to be within 1% of the corresponding experimental values over the entire range of temperatures studied. To further test the theory, we have demonstrated that the temperature variation of the average number of H-bonds per water molecule, calculated using the proposed theory with the above mentioned values for H and S, compares quite well with those estimated from various available spectroscopic and molecular simulation studies.

Accurate calculation of the dielectric constant of water from simulations of a microscopic droplet in vacuum

We present a successful calculatioon of the static dielectric constant of water based on simulations of microscopic droplets in vacuum. A 1.5 ns simulation of a 24 Å radius sphere of TIP3P water gives ϵ = 82 ± 5 at 292 K; a 2 ns simulation of a 14 Å sphere gives ϵ = 82 ± 5 at 294 K. Inclusion of all electrostatic interactions in the droplet was critical to success. Polar fluctuations in the inner half of the droplet are bulk-like, due to efficient screening by the outer half, despite the surrounding vacuum. This suggests that droplet simulations of more complex systems, such as proteins in water droplets, can successfully account for solvent screening of charges near the center of the simulation sphere.

The static dielectric constant of water at pressures up to 20 kbar and temperatures to 1273 K: Experiment, simulations, and empirical equations

The static dielectric constant of water was calculated by molecular dynamics simulations using the SPC/E water model up to 1273 K and pressures to 20 kbar. Simulations within the pressure-temperature range (up to 5 kbar and 823 K) of the available experimental data yield dielectric constant (ɛ) in very good agreement with experiment (within 5%) for all values of density ≤ 1.0 g/cm3. This demonstrates that the SPC/E model provides a valid means of obtaining the dielectric constant beyond the P, T range of the available data. Several previous attempts were made to extrapolate the experimental values of ɛ to high P, T conditions using semi-empirical fit equations. We tested two of these equations (Pitzer, 1983; Franck et al., 1990) against our simulated values of ɛ at densities of 0.322, 0.5 g/cm3 and 1.0 g/cm3 for temperatures ranging from 600–1200 K. For density ≤ 1 g/cm3 and temperatures above 600 K the equation of Franck et al. (1990) is in agreement with the simulations to within 7% and provides, therefore, a simple and valid method of extrapolation of the data.

The static dielectric constant of water at pressures up to 20 kbar and temperatures to 1273 K: Experiment, simulations, and empirical equations

The static dielectric constant of water at pressures up to 20 kbar and temperatures to 1273 K: Experiment, simulations, and empirical equations

Theoretical calculation of the static dielectric constant of water at high temperatures and pressures

Theoretical calculation of the static dielectric constant of water at high temperatures and pressures

Dielectric properties of water in the coexisting phases of aqueous polymeric two-phase systems

Complex permittivity of aqueous solutions of poly(ethylene glycol)(PEG), polyvinylpyrrolidone (PVP), Ficoll, dextran and of the phases of aqueous dextran–PEG, dextran–PVP, and dextran–Ficoll biphasic systems of varied polymer concentrations have been measured at four frequencies in the range 10–24 GHz at 25 °C by an interferometric transmission method. It is found that the static dielectric constant of water is enhanced in all the polymer solutions directly with the polymer concentration. The polymers examined slow down the reorientational motion of water molecules and the polymer concentration effect decreases in the order PEG > PVP > Ficoll > dextran, in accordance with the order of decrease of the relative hydrophobicity of the polymers. It is also established that the dielectric relaxation times of water in the coexisting phases of the systems studies are different. The results obtained support the hypothesis that phase separation in an aqueous mixture of two polymers results in the appearance of two different coexisting structures of water formed under different influences of the phase polymers on orientation and intermolecular interactions of the water molecules.

Thermophysical properties of supercritical fluids with special consideration of aqueous systems

Selected thermophysical properties of polar, dense supercritical fluids are discussed. The static dielectric constant of water and the freon R22 (CHClF 2) is shown in some detail. Examples of critical curves for binary systems with water and methanol are given. New experimental data of excess volumes up to 400 °C and 2000 bar are shown for water combined with H 2, CH 4 and benzene. Excess Gibbs energies and activity coefficients for water-benzene are also shown. Results of the solubility of anthracene in ten different high pressure fluids, obtained by UV-spectroscopy, are presented. The PVT-data of concentrated supercritical aqueous NaCl-solutions and the ion product of pure water to 1000 °C are discussed.

Electric polarisation of water: Monte Carlo studies

Monte Carlo calculations for liquid water in strong static electric fields are used to study dielectric, thermodynamic and structural properties. Emphasis is placed on the importance of long range interactions, particularly effects due to spherical truncation of the pair potential and to the Onsager reaction field. The Rowlinson model for pair interactions is not capable of predicting the high static dielectric constant of water and similar results are to be expected for other point charge models. It is shown that dielectric constants are very sensitive to the Onsager reaction field, whereas thermodynamic properties are somewhat insensitive. Structural effects due to dielectric saturation are demonstrated and the influence of long range interactions on such properties discussed.

Static Dielectric Constant of Water and Steam

This paper reviews and evaluates the experimental works of the static dielectric constant (permittivity) of water and steam over the century. The critically evaluated experimental data are represented by a function of temperature and density. This representation was carefully examined in the light of the criteria for smoothness and physical plausibility. As a result of this work, which was largely stimulated by the activities of the International Association for the Properties of Steam, a new International formulation for the static dielectric constant of water and steam was adopted. This formulation covers a temperature range from 0 to 550 °C and a pressure range up to 500 MPa.