Dielectric Properties Of Polar Liquids Research Articles

Screening of Coulomb interactions in liquid dielectrics

The interaction of charges in dielectric materials is screened by the dielectric constant of the bulk dielectric. In dielectric theories, screening is assigned to surface charges appearing from preferential orientations of dipoles along the local field in the interface. For liquid dielectrics, such interfacial orientations are affected by the interfacial structure characterized by a separate interfacial dipolar susceptibility. We argue that dielectric properties of polar liquids should be characterized by two distinct susceptibilities responsible for local response (solvation) and long-range response (dielectric screening). A microscopic model for dipolar screening in polar liquids is developed here. It shows that the standard bulk dielectric constant is responsible for screening at large distances. The potential of mean force between ions in polar liquids becomes oscillatory at short distances. Oscillations arise from the coupling of collective longitudinal excitations (dipolarons) of the polar liquid with its interfacial density profile. Interfacial electrostatics demonstrates a crossover beyond the solute radius of ∼1 nm from the scaling laws roughly consistent with continuum expectations for small solutes to new scaling trends characterizing the much softer nano-scale solute–solvent interface. This crossover also marks the transition to a continuum-type electrostatic screening between ions, when short-distance oscillation of the potential of mean force become strongly damped. Screening oscillations are enhanced for more structured interfaces.

Investigating Antibody Interactions with a Polar Liquid Using Terahertz Pulsed Spectroscopy

In this article, we use terahertz spectroscopy to study the dielectric properties of the peroxidase-conjugated affinity purified goat anti-cat immunoglobulin G and the fluorescein-conjugated affinity purified goat anti-cat immunoglobulin G when they interact with polar liquids. The influence of protein concentration, as well as presence of glycerol as a cosolvent, is determined by estimation of the effective hydration shell radius of the protein in solution. The dielectric spectra in this study are measured over the frequency range 0.1–1.3 THz and it is found that the dielectric properties are dependent on the type of the charges in the hydrogen-bonded antibodies' networks. Our results indicate that the terahertz dielectric properties of polar liquids are strongly affected by the presence of the antibody and suggest that the dielectric spectrum is particularly powerful in the study of structural and conformational properties of proteins. Therefore, terahertz spectroscopy is a very sensitive approach to investigate structural features of biological systems.

Interparticle correlations and magnetic properties of concentrated ferrocolloids

A statistical mechanical model was proposed for describing magnetic properties of highly concentrated ferrocolloids and dielectric properties of polar liquids. The model is based on a relationship between the magnetization and the pair correlation function of a spatially homogeneous ferroparticle system. The advantage of the proposed method is that the determination of the pair distribution function, with an accuracy of the powers of the concentration nk and the powers of the interparticle dipole-dipole interaction potential Udk, leads to an expression for the magnetization of the order of nk+1 and Udk+1, respectively. Relations for the magnetization and the magnetic susceptibility of a ferrofluid and also for the permittivity of a polar liquid taking into account interparticle correlations with an accuracy of terms ∼Ud2 were derived. The results obtained within the framework of this model agree closely with the numerical calculations and experimental data.

Molecular dynamics simulation of the wave vector-dependent static dielectric properties of methanol–water mixtures

The static wave vector-dependent dielectric properties of methanol–water mixtures at room temperature are investigated through molecular dynamics simulation. We report results for the transverse and longitudinal components of the permittivity tensors, as well as the short- and long-ranged portions of the Kirkwood g factors at small wave vectors k, calculated from the mean squared dipole densities for mixtures of different compositions. In addition, we have calculated dipolar symmetry projections h110(r) and h112(r) of the pair distribution functions for each mixture and determined the asymptotic behavior of the second projection at large distance r. We find that h110(r) and h112(r) as well as their contributions from different molecular pairs are strongly composition dependent, but that the resulting Kirkwood correlation factor is nearly independent of composition. We obtained the dielectric tensor ε(k) over a wide range of k using Fourier–Hankel transforms of h110(r) and h112(r). Our results indicate that this real space route is an attractive alternative approach to the static, k-dependent dielectric properties of polar liquids. The k-dependent transverse components of the permittivities obtained this way are in good agreement with the values calculated from the mean squared dipole densities. The longitudinal permittivities, on the other hand, show a less satisfactory agreement at small wave vectors due to inaccuracies in the numerical transforms.

The distribution of fluctuations of the total dipole moment in polar liquids

By P. G. KUSALIK Department of Chemistry, Dalhousie University, Halifax, Nova Scotia, B3H 4J3, Canada {Received 21 June 1993; accepted 12 July 1993) The distribution of fluctuations o f the total dipole moment in polar liquids is characterized. The functional form of the probability distribution function, P(g), where g is proportional to the square of the total moment and its average value is directly related to the static dielectric constant, is empirically deter­mined. A formal justification of the functional form is then developed and impli­cations to the calculation of the dielectric constant in computer simulations are discussed. The dielectric properties of polar liquids, particularly the static dielectric constant e, are fundamental characteristics of these systems [1]. Unfortunately, the deter­mination of these properties by computer simulation has presented both conceptual [2-7] and computational difficultie [7-16] Man.sy of the problems associated with the treatment of the boundary conditions have now been resolved, yet many impor­tant questions concerning the influences of the boundary conditions and finite-size samples have remained at least partially unanswered [14-16]. Furthermore, although reasonably precise values for e for highly polar liquids (such as water) can be determined with rather long simulations, the results obtained may still contain non-trivial systematic errors due to the effects of system size and boundary con­ditions (for examples, see [13-15]). Clearly, there is a need for more computationally efficient routes to e and for an increased understanding of the influences of sample size and boundary conditions upon the dielectric properties of polar liquids. The traditional means of obtaining the static dielectric constant from a computer simulation has been from the average fluctuations in the total dipole moment of the system, M, through the standard relationship (valid for both reaction-field and periodic boundary conditions [3, 5]) (

On the computer simulation of highly polar fluids using large systems

The determination of the dielectric properties of polar liquids by computer simulation has, in the past, presented both conceptual and computational difficulties. Many of the conceptual problems have now been at least partially resolved, yet the accurate calculation of the dielectric response for a highly polar liquid remains a major computational task. The usual means of obtaining the static dielectric constant, ϵ, is through the fluctuations in the total dipole moment of the system. In this paper we describe an alternate approach which relies upon the long-range asymptotic behaviour of the dipole-dipole correlations in order to determine ϵ. It requires that a rather large simulation cell be employed, in the present case samples of 4000 particles. Molecular dynamics simulations have been performed for a highly polar fluid composed of dipolar soft spheres in which the dipole-dipole interactions have been evaluated using the Ewald summation technique. Results for the static dielectric constant are reported...

Influence of inertia on the dielectric properties of polar liquids. Application to deoxyhemoglobin S

In this paper, we have derived oscillator relations, including inertial effects, which are an extension of the Debye relations, and have shown their interest together with their limits of application. These relations may be applied as soon as the dimensionless damping parameter γ is less than 10, and yield a lot of information on the molecular structure of the medium. We have used them in the study of an abnormal hemoglobin, termed deoxyhemoglobin S, from experimental data of dielectric constants obtained by Delalic et al. Our calculation is based upon the Kramers-Kronig method. By means of a best-fit procedure of the dispersion plots together with the Cole-Cole plots, the presence of a monomeric phase and of three main aggregates which are well characterized, is found. So, we get several stereotypes of the medium, and its time evolution is interpreted in terms of molecular parameters. We calculate the moment of inertia of these aggregates and we give the evolution of the friction coefficient ξ. We remark that the decrease of γ corresponds to an ordered array of the medium and that its limiting value equal to 1.6 is related to a gel state, in full agreement with the theoretical estimate obtained by Coffey.

The computer simulation of the dielectric properties of polar liquids. The dielectric constant and relaxation of liquid hydrogen chloride

We present simulation results for a heteronuclear-diatomic-molecular fluid for a particular intermolecular potential (Model A of reference 1) for the dielectric response for various states using a perturbation-and-difference method. We find that there is a tendency to antiparallel orientation of the dipoles in the low temperature, high density liquid. The correlation of orientation changes with increasing temperature to a weak tendency to parallel orientation in the high temperature liquid and the supercritical fluid. This method of calculation is better than the conventional direct method but the accuracy obtained for reasonable computing times is still low. Here it is approximately ± 5 per cent. This potential reproduces many of the properties of fluid hydrogen chloride quite well [1, 2, 3]. The dielectric properties deduced from this simulation are compared with the experimental values. Given the difficulty of accounting properly for the electronic polarizability, the agreement with experiment for the ...

Effect of the nature of the metal on the dielectric properties of polar liquids at the interface with electrodes. A phenomenological approach

Effect of the nature of the metal on the dielectric properties of polar liquids at the interface with electrodes. A phenomenological approach

Effect of the nature of the metal on the dielectric properties of polar liquids at the interface with electrodes. A phenomenological approach

The dielectric behaviour of water, DMSO and ACN at the interface with transition and non-transition metals is examined by analysing the inner-layer capacity as a function of the metal surface chemical affinity. An, inner-layer capacity in the absence of metal-solvent specific interaction is defined and derived by graphical correlations. The permittivity of the surface phase of the solvent under these conditions is derived and analysed to elucidate the nature of the factors contributing to the dielectric behaviour at an interface. The capacity-potential curves for Fe, as a typical transition metal, are elaborated to investigate the orientation of the solvent on the surface and the applicability of the Gouy-Chapman-Stern model. Suggestions on the nature of the metal-water surface bond are given on the basis of the derived parameters. The structure of the double layer in ACN at transition metals is discussed in the light of recent measurements.

Theoretical analysis of dielectric properties of polar liquids in the far-infrared spectral range

The Zwanzig-Mori theory is applied to the study of dielectric behavior of polar liquids in the far-infrared spectral range. The basic dynamical variables on which the calculation is based are the macroscopic dipole moment $\stackrel{\ensuremath{\rightarrow}}{\mathrm{M}}(t)$ of the liquid sample and its time derivatives. The return to transparency and the excess absorption are analyzed in detail. It is shown that the spectral behavior of pure liquids can be described by the same formulas as those applicable to analyze diluted solutions provided microscopic time parameters of the latter theories are replaced by new macroscopic time parameters chosen in an appropriate way.

Dielektrische Messungen an Cyclanonen. III. Dielektrisches Verhalten von Cyclotridecanon

AbstractThe dielectric behavior of cyclotriclecanone in solid and liquid phase has been studied. The liquid shows the dielectric properties of polar liquids, but the relaxation time is about 10 times higher than in liquid cyclohexanone and ‐heptanone. The solid phase represents a new type of dielectric behavior in the cyclanone series: The static dielectric constant increases steadily with decreasing temperature between the melting point and 100°C. The solid shows in the temperature intervall relaxation of the Cole type; there are probably two different mechanisms with relaxation parameters τ0 of 10−7 and 5.10−10 respectively.