Alexander Puzenko

Non-Debye dielectric relaxation in complex materials

Abstract The paper considers several examples of non-Debye dielectric response in complex heterogeneous media. The percolation phenomenon and Cole–Cole relaxation in disordered matter are discussed in detail. The proposed models are illustrated by different sample systems: ionic microemulsions, porous glasses, porous silicon, polymer–water mixtures, and polymer–microcomposite materials. The models enable us to establish the relationship between the parameters of dielectric relaxation broadening, structural properties of the media and transport features of charge carriers in the considered systems. In addition, the origins of “strange kinetic” phenomena were discussed based on statistical physics and fractional time evolution ideas.

The electromagnetic response of human skin in the millimetre and submillimetre wave range

Recent studies of the minute morphology of the skin by optical coherence tomography revealed that the sweat ducts in human skin are helically shaped tubes, filled with a conductive aqueous solution. This, together with the fact that the dielectric permittivity of the dermis is higher than that of the epidermis, brings forward the supposition that as electromagnetic entities, the sweat ducts could be regarded as low Q helical antennas. The implications of this statement were further investigated by electromagnetic simulation and experiment of the in vivo reflectivity of the skin of subjects under varying physiological conditions (Feldman et al 2008 Phys. Rev. Lett. 100 128102). The simulation and experimental results are in a good agreement and both demonstrate that sweat ducts in the skin could indeed behave as low Q antennas. Thus, the skin spectral response in the sub-Terahertz region is governed by the level of activity of the perspiration system and shows the minimum of reflectivity at some frequencies in the frequency band of 75-110 GHz. It is also correlated to physiological stress as manifested by the pulse rate and the systolic blood pressure. As such, it has the potential to become the underlying principle for remote sensing of the physiological parameters and the mental state of the examined subject.

Dielectric spectra broadening as the signature of dipole-matrix interaction. I. Water in nonionic solutions

Whenever water interacts with another dipolar entity, a broadening of its dielectric relaxation occurs. Often this broadening can be described by the Cole-Cole (CC) spectral function. A new phenomenological approach has been recently presented [A. Puzenko, P. Ben Ishai, and Y. Feldman, Phys. Rev. Lett. 105, 037601 (2010)] that illustrates a physical mechanism of the dipole-matrix interaction underlying the CC behavior in complex systems. By considering the relaxation amplitude Δε, the relaxation time τ, and the broadening parameter α, one can construct a set of 3D trajectories, representing the dynamic behavior of different systems under diverse conditions. Our hypothesis is that these trajectories will contribute to a deeper understanding of the dielectric properties of complex systems. The paper demonstrates how the model describes the state of water in aqueous solutions of non-ionic solutes. For this purpose complex dielectric spectra for aqueous solutions of D-glucose and D-fructose are analyzed.

Dielectric spectroscopy data treatment: I. Frequency domain

The computational methods for complex dielectric permittivity data treatment are considered in this paper. The dielectric spectroscopy data analysis in the frequency domain can be reduced to the problem of choosing the appropriate model functions and an estimation of their model parameters. To address the latter problem a method has been formulated based on a penalized maximum likelihood approach, for obtaining a smooth estimate for the model parameters expressed as functions of temperature. The use of the Hilbert transform (Kramers?Kronig relation) for dc conductivity evaluation directly from the complex dielectric permittivity data has been explored as well. In this paper a numerical algorithm for this procedure, using the fast Fourier transforms and a suitable interpolation technique, is suggested. Based on these methods, state-of-the-art software for dielectric spectroscopy data analysis in the frequency domain has been developed.

Dielectric relaxation of porous glasses

Abstract The dielectric properties of porous glasses, obtained from sodium borosilicate glass, were investigated in the frequency range 20 Hz to 1 MHz and temperature range −100°C to +300°C for the purpose of inferring the geometric properties of porous materials. The features of the dielectric properties due to the geometrical disorder were analysed by using models describing the non-Debye slow decay dynamics. The dielectric response is affected by the geometrical micro- and mesostructural properties of the porous matrix and the properties of the material filling the pores. It provides information on the hindered dynamics of water molecules, located within the pores and affected by the surfaces. An analysis of the dielectric parameters enables us to describe the porosity of the materials.

The role of GLUT1 in the sugar-induced dielectric response of human erythrocytes.

We propose a key role for the glucose transporter 1 (GLUT1) in mediating the observed changes in the dielectric properties of human erythrocyte membranes as determined by dielectric spectroscopy. Cytochalasin B, a GLUT1 transport inhibitor, abolished the membrane capacitance changes in glucose-exposed red cells. Surprisingly, D-fructose, known to be transported primarily by GLUT5, exerted similar membrane capacitance changes at increasing D-fructose concentrations. In order to evaluate whether the glucose-mediated membrane capacitance changes originated directly from intracellularly bound adenosine triphosphate (ATP) or other components of the glycolysis process, we studied the dielectric responses of swollen erythrocytes with a decreased ATP content and of nucleotide-filled ghosts. Resealed ghosts containing physiological concentrations of ATP yielded the same glucose-dependent capacitance changes as biconcave intact red blood cells, further supporting the finding that ATP is the effector of the glucose-mediated dielectric response where the ATP concentration is also the mediating factor in swollen red blood cells. The results suggest that ATP binding to GLUT1 elicits a membrane capacitance change that increases with the applied concentration gradient of D-glucose. A simplified model of the membrane capacitance alteration with glucose uptake is proposed.

The Helical Structure of Sweat Ducts: Their Influence on the Electromagnetic Reflection Spectrum of the Skin

The helical structure of human eccrine sweat ducts, together with the dielectric properties of the human skin, suggested that their electromagnetic (EM) properties would resemble those of an array of helical antennas. In order to examine the implications of this assumption, numerical simulations in the frequency range of 100-450 GHz, were conducted. In addition, an initial set of measurements was made, and the reflection spectrum measured from the skin of human subjects was compared to the simulation results. The simulation model consisted of a three layer skin model (dermis, epidermis, and stratum corneum) with rough boundaries between the layers and helical sweat ducts embedded into the epidermis. The spectral response obtained by our simulations coincides with the analytical prediction of antenna theory and supports the hypothesis that the sweat ducts can be regarded as helical antennas. The results of the spectrum measurements from the human skin are in good agreement with the simulation results in the vicinity of the axial mode. The magnitude of this response depends on the conductivity of sweat in these frequencies, but the analysis of the phenomena and the frequencies related to the antenna-like modes are independent of this parameter. Furthermore, circular dichroism of the reflected electromagnetic field is a characteristic property of such helical antennas. In this work we show that: 1) circular dichroism is indeed a characteristic of the simulation model and 2) the helical structure of the sweat ducts has the strongest effect on the reflected signal at frequencies above 200 GHz, where the wavelength and the dimensions of the ducts are comparable. In particular, the strongest spectral response (as calculated by the simulations and measured experimentally) was noted around the predicted frequency (380 GHz) for the axial mode of the helical structure.

Measurement and simulation of conductive dielectric two-layer materials with a multiple electrodes sensor

Impedance spectroscopy has been shown to provide a great potential as a measuring technique for monitoring human blood glucose. The two major potential benefits are the ability to perform non-invasive and continuous measurements. Previous work has outlined the range of challenges of such an impedance based technique. Our impedance sensor is composed of several capacitive fringing field electrodes with various characteristic geometries to achieve the desired penetration depths in human skin and the underlying tissue. A comparison of the measurements made on reference materials of known dielectric properties with the results of electromagnetic field simulations allows sensor characterization to be achieved and provides the ability to optimize the sensor geometry. Such comparisons reveal that the measurements and simulations are in qualitative agreement with the expected impedance behavior, i.e. there is a larger sensitivity to changes in the dielectric properties of the deeper layer for electrodes with a deeper penetration of the electromagnetic field (EMF). Another conclusion is that, despite the approximations made in the simulation process, the measured and simulated quantities agree. This opens the possibility to use simulations to define the functional relation between the measured impedances and the layers dielectric parameters in order to correlate impedance changes with glucose concentration changes.

DIELECTRIC RELAXATION OF WATER IN CLAY MINERALS

The 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.

The dielectric response of interfacial water—from the ordered structures to the single hydrated shell

Water is the universal solvent in nature. Does this imply, however, that its interaction with its environment is also a universal feature? While this question maybe too fundamental to be answered by one method only, we present evidence that the broadening of the dielectric spectra of water presents universal features of dipolar interactions with different types of matrixes. If in aqueous solutions the starting point of water’s state can be considered as bulk, with only partial interactions with the solute, then the state of water adsorbed in heterogeneous materials is determined by various hydration centers of the inhomogeneous material (the matrix) and it is significantly different from the bulk. In both cases, the dielectric spectrum of water is symmetrical and can be described by the Cole–Cole (CC) function. The phenomenological model that describes a physical mechanism of the dipole–matrix interaction in complex systems underlying the CC behavior has been applied to water adsorbed in porous glasses. It was then extended to analyses of the dynamic and structural behavior of water in nonionic and ionic aqueous solutions. The same model is then used to analyze the CC relaxation processes observed in clays, aqueous solutions of nucleotides, and amino acids.