Microwave Dielectric Relaxation Research Articles

Random Forest Regression Analysis for Estimating Dielectric Properties in Epoxy Composites Doped with Hybrid Nano Fillers

Bisphenol-A resin epoxy resin composites doped with various concentrations of inorganic hybrid nanofillers, TiO2 + ZnO, were thoroughly examined in the research described in this report for their microwave dielectric relaxation spectroscopy. Ultrasonic dispersion techniques were used to disperse the TiO2 + ZnO hybrid nanofiller into the Bisphenol-A resin. X-ray diffraction (XRD) was employed to ascertain the structural characteristics of the TiO2 and ZnO nanoparticles (NPs) and TiO2 + ZnO hybrid NPs doped neat epoxy (epoxy + hardener). A Vector network analyzer was used to measure the dielectric properties of the hybrid NPs doped neat epoxy in the frequency range from 200 MHz to 20 GHz. Our findings offer important new perspectives on the polarization mechanisms and structural properties of these composite materials. The complex relationship between frequency and dielectric characterization led to measurement complexities that often come with extensive time and cost requirements. This paper presents the random forest regression model as an effective method for predicting the frequency-dependent dielectric constants in composite materials. The main objective of this study was to examine the performance metrics, such as the adjusted R-squared score, root mean squared error (RMSE), and mean absolute error (MAE), across various values of the minimum node size parameter (n min). This study showcases the effectiveness of the RF regression model to accurately and efficiently predict the frequency-dependent dielectric constants in composites. As a result, it eliminates the requirement for laborious and expensive laboratory testing.

(Invited) Microwave Dielectric Relaxation Spectroscopy: A Technique to Inform Ion Transport in Hydrated Polymer Membranes

Providing sustainable supplies of purified water and energy is a critical global challenge for the future, and polymer membranes will play a key role in addressing these clear and pressing global needs for water and energy. Polymer membrane-based processes dominate the desalination market because they are more energy efficient than thermal desalination processes, and polymer membranes are crucial components in several rapidly developing power generation and energy storage applications that rely on membranes to control, selectively, rates of ion transport. Much remains unknown about the influence of polymer structure on basic intrinsic transport properties, and these relationships are important for designing next generation polymer membrane materials.Key to controlling ion transport in membranes for water purification and energy applications is engineering interactions between ions and the solvated polymer matrix. Microwave dielectric relaxation spectroscopy is a tool that enables study of hydrated polymer membranes because water molecule dipoles can be probed in the microwave frequency region. This technique can provide unique insight into hydrated polymer dielectric permittivity (or dielectric constant) properties, which are critical in emerging thermodynamic modeling of ion transport in hydrated polymers. This presentation discusses the use of microwave dielectric relaxation spectroscopy to uncover structure property relationships in hydrated polymers and, more broadly, presents an overview of research aimed at further understanding fundamental structure/property relationships that govern small molecule transport in polymeric materials considered for desalination and electric potential field-driven membrane applications that can help address global needs for clean water and energy.

Microwave Dielectric Relaxation of Univalent and Bivalent Electrolyte Solutions.

The microwave dielectric relaxation of aqueous solutions of univalent (KCl, NaCl, NaI) and bivalent (CaCl2, MgCl2) electrolytes at concentrations between 0.1 and 1 M at 25 °C was investigated using a vector network analyzer (0.5≤ ν ≤ 40 GHz). The spectra of these electrolyte systems are characterized by a symmetrical broadening of the main relaxation peak and were fitted using the Cole-Cole equation. In our analysis, we provide insights into the underlying physics of the relaxation events at microscopic and mesoscopic scales by using a 3D phase space trajectory that is based on the interactions of the relaxing dipole units with their surroundings and Frohlich's B function. The effect of the solutes on the H-bond network of water with increasing concentration is evident in the microwave dielectric spectra through decreasing dielectric strengths and relaxation times. It was found that the number of perturbed water molecules is higher in the case of bivalent electrolytes and appears to be proportional to the ionic radius. In our approach, the particular dependence between the broadening parameter α and the relaxation times τ reflects the rate of interactions between the elementary dipole units and their surroundings. We provide a quantitative analysis of the level of perturbation caused by the presence of ions in the hydrogen-bond network of water. It was found that the H-bonded network of water is highly perturbed in univalent systems compared to bivalent systems due to weaker bonded hydration shells. Finally, we found significant differences between the dielectric response of NaCl and NaI. The differences, originating in the counterions Cl- and I-, which are characterized by large ionic radii and consequently weaker electric fields in their vicinity, confirm that the effect of weakly hydrated ions should not be neglected in microwave dielectric spectra analysis.

Microwave dielectric properties and relaxation characteristics of Ba0.5Sr0.5TiO3 –Bi2MoO6 composite ceramics

The (1-x) Ba0.5Sr0.5TiO3-xBi2MoO6 (x = 10, 20, 30, and 40 wt%) composite ceramics were successfully synthesized through a conventional solid-phase reaction method, and the influence of A- and B- site co-doping on the dielectric properties of the BST composite ceramics was comprehensively investigated. Bi3+ ions acted as donors to replace Ba2+ and Mo6+ replaced Ti4+, producing a (BiBa∙ + MoTi∙∙)-VBa″ dipole to achieve electrovalent equilibrium. In addition, the liquid phase inhibited the growth of grains and promoted densification of the composite ceramics. The degree of B-site order was analyzed using Raman spectroscopy. With an increase in the amount of Bi2MoO6 composite, the dielectric permittivity peak broadened, the Curie temperature gradually decreased, and the tunability of the composite ceramics declined gradually. The dielectric properties of the composite ceramics benefitted from the inclusion of Bi2MoO6 and its composite effects. At the composition of x = 30 wt%, the composite ceramics exhibited excellent comprehensive properties with ε = 457 (RT), T = 14% (at 30 kV/cm), and Q = 780 (at 1148 MHz).

Nonthermal acceleration of protein hydration by sub-terahertz irradiation

The collective intermolecular dynamics of protein and water molecules, which overlap in the sub-terahertz (THz) frequency region, are relevant for expressing protein functions but remain largely unknown. This study used dielectric relaxation (DR) measurements to investigate how externally applied sub-THz electromagnetic fields perturb the rapid collective dynamics and influence the considerably slower chemical processes in protein–water systems. We analyzed an aqueous lysozyme solution, whose hydration is not thermally equilibrated. By detecting time-lapse differences in microwave DR, we demonstrated that sub-THz irradiation gradually decreases the dielectric permittivity of the lysozyme solution by reducing the orientational polarization of water molecules. Comprehensive analysis combining THz and nuclear magnetic resonance spectroscopies suggested that the gradual decrease in the dielectric permittivity is not induced by heating but is due to a slow shift toward the hydrophobic hydration structure in lysozyme. Our findings can be used to investigate hydration-mediated protein functions based on sub-THz irradiation.

Hyper-mobile Water and Raman 2900 cm-1 Peak Band of Water Observed around Backbone Phosphates of Double Stranded DNA by High-Resolution Spectroscopies and MD Structural Feature Analysis of Water.

High-resolution measurements of microwave dielectric relaxation and Raman spectroscopies for waters in double-stranded (ds) 10-mer DNA solution revealed the presence of hyper-mobile water (HMW) and a marked OH stretching band appearing in the range from 2500 to 3100 cm-1, here called the LA band, at the low wavenumber tail of the major OH stretching band of water. Quantitation of the Raman scattering intensity for ds 10-mer DNA in phosphate or tris(hydroxymethyl)aminomethane (TRIS) buffers showed that the LA band was formed by 2000-3000 water molecules per ds 10-mer DNA, indicating collective OH stretching vibrations of water molecules around the backbone phosphate oxygen atoms. The LA band intensity of ds 10-mer DNA in 10 mM TRIS increased and decreased by 30% with the addition of 2 mM MgCl2 and 2 mM CaCl2, respectively. The LA band intensity and the effect of adding Mg(II) or Ca(II) ions to the band intensity were maintained in the presence of 0.14 M KCl; however, the changes induced by the divalent cations were reduced by half. Molecular dynamics calculations of water molecules around the backbone phosphate groups of ds 10-mer DNA indicate the presence of high-density water and broad regions of fluctuating water density, suggesting that they correspond to HMW and the LA band, respectively.

Dielectric relaxation and dipole moment studies of hydrogen bonded complexes for enanthamide and valeramide with halogenated phenols using J-band microwave frequency

Dielectric investigations of hydrogen bonded complexes of Enanthamide and Valeramide with 4-bromophenol, 4-chlorophenol, 4-iodophenol and 4-fluorophenol in benzene were done at 303K, using a J-band (7.22GHz) microwave bench and dielectric relaxation setup. The permittivity of amides with halogenated phenol binary mixtures was measured in the microwave frequency range at temperatures ranging from 298K to 323K. At microwave frequencies; dielectric relaxation of ternary mixes of polar liquids in nonpolar fluids has been explored. Such investigations give useful information about the intermolecular and intramolecular interactions of solutes and solvent molecules. The dipole meter had a measurement frequency of 2MHz. The different parameters of dielectric, relaxation time (τ 0 ) and the dipole moment (μ) has been evaluated using the single-frequency concentration Higasi approach. The fact that the relaxation time and molar free energy activation of the 1:1 molar ratio are greater than those of other higher molar ratios (i.e. 3:1, 2:1, 1:2, 1:3) confirms the presence of a 1:1 complex structure between the studied systems, as well as a complex formation between the free hydroxyl group of phenols and the carbonyl group of amides. The dielectric relaxation energy parameters (ΔFε, ΔHε and ΔSε) of amides with halogenated phenols in benzene have been computed and compared with the related viscosity parameters. A comparison of these two sets of characteristics reveals that dielectric relaxation, like viscous flow, may be thought of as rate process.

Effect of the selective localization of carbon nanotubes and phase domain in immiscible blends on tunable microwave dielectric properties

In recent years, the immiscible polymer blend system has attracted much attention as the matrix of nanocomposites. Herein, from the perspective of dynamics, the control of the carbon nanotubes (CNTs) migration aided with the interface of polystyrene (PS) and poly (methyl methacrylate) (PMMA) blends was achieved through a facile melt mixing method. Thus, we revealed a comprehensive relationship between several typical CNTs migrating scenarios and the microwave dielectric properties of their nanocomposites. Based on the unique morphologies and phase domain structures of the immiscible matrix, we further investigated the multiple microwave dielectric relaxation processes and shed new light on the relation between relaxation peak position and the phase domain size distribution. Moreover, by integrating the CNTs interface localization control with the matrix co-continuous structure construction, we found that the interface promotes double percolation effect to achieve conductive percolation at low CNTs loading (~1.06 vol%). Overall, the present study provides a unique nanocomposite material design symphonizing both functional fillers dispersion and location as well as the matrix architecture optimization for microwave applications.

Molecular interaction in binary mixtures of 3-Bromoanisole and methanol: A microwave dielectric relaxation spectroscopy and molecular dynamic simulation study

Complex permittivity spectra for the binary mixtures of 3-bromoanisole (3-BA) and methanol (MeOH) with varying concentrations at different temperatures (T = 293.15 to 323.15 K) were obtained over a broad microwave frequency range. The complex permittivity data were fitted to different dielectric relaxation models using complex nonlinear least square fitting method. From the best fitting model dielectric relaxation parameters were extracted. Concentration dependence of the dielectric relaxation parameters were used to gain information about the molecular interaction among the constituent of the mixtures. The formation and deformation of H-bonds among the molecules of the mixture are discussed using wait-and-switch model. Temperature and concentration dependent static permittivity provided information about the alignment and cross-linkage of molecules in liquid mixtures. Molecular dynamics (MD) simulations of mixtures of 3-BA and MeOH at 293.15 K temperature have also been conducted to gain additive information regarding molecular interaction and to justify the inferences derived from the experimental microwave complex permittivity data.

Microwave dielectric relaxation spectroscopy of paracetamol and its aqueous solutions

The complex dielectric function ε∗(ω) = ε ′ (ω) – jε ″ (ω) is studied for aqueous solutions of Paracetamol (PCM) (at four different temperatures 293.15 K, 303.15 K, 313.15 K and 323.15 K) across the frequency range of 200 MHz to 30 GHz and of pure PCM in pellet form (at a constant temperature of 300.15 K) over the frequency ranging from 200 MHz to 20 GHz. Dielectric properties are measured using Anritsu Shockline Vector Network Analyser (VNA) Model No. MS46322A, SPEAG DAK – 1.2 (5–50 GHz) and DAK – 3.5 (200 MHz–20 GHz) probes. Obtained dielectric data are further analysed with Debye relaxation model in order to understand the dipolar relaxation behaviour of these solutions. From obtained dielectric data; other parameters like power reflected (Pr), power transmitted (Pt), penetration depth (dp) have also been determined at 2.45 GHz and analysed in view of its applicability for microwave dielectric heating in pharmaceuticals. Temperature dependence of the dipolar relaxation time is used to evaluate thermodynamical parameters: Gibbs free energy of activation (ΔFe), entropy of activation (ΔSe) and enthalpy of activation (ΔHe).

Functional group configuration influences salt transport in desalination membrane materials

Five methacrylate-based co-polymers, which have different ratios of 2-hydroxyethyl methacrylate (HEMA) and glycerol methacrylate (GMAOH) co-monomers, were prepared to investigate the influence of functional group configuration on salt transport properties. The HEMA and GMAOH co-monomers were selected because of the differences in position and number of hydroxyl groups in the two molecules. Co-polymer composition was varied systematically from a vicinal diol-rich (GMAOH-rich) configuration to a distributed hydroxyl group (HEMA-rich) configuration. To decouple the impact of functional group configuration and of changing water content on transport properties, all of the materials were prepared to have statistically equivalent water content. Salt sorption was lower and salt diffusion was slower in the HEMA-rich configuration compared to the GMAOH-rich configuration. Microwave dielectric relaxation spectroscopy revealed lower relative permittivity (i.e., dielectric constant) for the HEMA-rich co-polymers, which is consistent with suppressed salt sorption in those materials compared to the GMAOH-rich co-polymers. This observation was complemented by state of water analysis that suggested freezable (i.e., bulk-like) water content decreased as HEMA content increased. Both results suggest that stronger interactions between water molecules and the polymer are favored when hydrophilic functional groups are distributed more evenly throughout the material. These results suggest that functional group position in hydrated polymers influences salt transport properties, and engineering polymers that have a distributed functional group configuration may suppress salt transport properties, which could result in favorable materials for desalination membranes.

Microwave dielectric relaxation & polarization study of binary mixture of methylethylketone with nitrobenzene

Present paper reveals detailed study of dielectric relaxation and dielectric polarization and physicochemical study of binary polar-polar liquid mixture i.e. dielectric constant, relaxation time, viscosity, density of methylethylketone (MEK) with nitrobenzene (NB) at 303 K. The measured dielectric and physicochemical parameters employed to acquire additional derived properties like Bruggeman factor, molar refraction and excess properties like static dielectric constant, excess inverse relaxation time, excess molar volume, excess viscosity, excess molar refraction, Gibbs free energy, and enthalpy of activation. The variation of this parameters with composition of these quantities has been used to explain the type, strength and nature of intermolecular interactions between MEK+NB binary mixture. Attained results authenticate that there are strong hydrogen-bond interactions between unlike molecules of different groups of MEK+NB mixtures and that 1:1 complexes are produced and strength of intermolecular interaction rises with rise in concentration of MEK. KEY WORDS : Bruggeman factor, Excess inverse relaxation time, Dielectric polarization Bull. Chem. Soc. Ethiop. 2019 , 33(2), 349-358. DOI: https://dx.doi.org/10.4314/bcse.v33i2.15

Microwave dielectric relaxation spectroscopy studies on associative polar binary mixtures of nitrobenzene with primary alcohols

The microwave dielectric relaxation behavior of binary mixtures of nitrobenzene with primary alcohols namely ethanol, 1-propanol and 1-butanol has been studied at different temperatures using Time Domain Reflectometry method. The measured complex dielectric spectra of pure and mixture solutions have been fitted with Debye model using least square method. The obtained static dielectric and relaxation time constant values are plotted against mole fraction of solute. The important dielectric parameters such as excess dielectric constant, excess inverse relaxation time and effective Kirkwood correlation factors are computed and the same has been used to interpret the intermolecular interaction and dynamic change in the solution. Furthermore, the mixing effect of nitrobenzene in different chain length alcohols has been explored by concentration dependent excess dielectric constant values. The positive molar enthalpy values of mixtures indicate that the heat energy is absorbed owing to the process of dipole reorientation. Moreover, the heterogeneous interaction between solute and solvent molecular functional groups has been confirmed by equi-molar FT-IR spectra analysis.

Strong Dependence of Hydration State of F-Actin on the Bound Mg2+/Ca2+ Ions

Understanding of the hydration state is an important issue in the chemomechanical energetics of versatile biological functions of polymerized actin (F-actin). In this study, hydration-state differences of F-actin by the bound divalent cations are revealed through precision microwave dielectric relaxation (DR) spectroscopy. G- and F-actin in Ca- and Mg-containing buffer solutions exhibit dual hydration components comprising restrained water with DR frequency f2 (<fw: DR frequency of bulk solvent, 17 GHz at 20 °C) and hypermobile water (HMW) with DR frequency f1 (>fw). The hydration state of F-actin is strongly dependent on the ionic composition. In every buffer tested, the HMW signal Dhyme (≡ (f1 - fw)δ1/(fwδw)) of F-actin is stronger than that of G-actin, where δw is DR-amplitude of bulk solvent and δ1 is that of HMW in a fixed-volume ellipsoid containing an F-actin and surrounding water in solution. Dhyme value of F-actin in Ca2.0-buffer (containing 2 mM Ca(2+)) is markedly higher than in Mg2.0-buffer (containing 2 mM Mg(2+)). Moreover, in the presence of 2 mM Mg(2+), the hydration state of F-actin is changed by adding a small fraction of Ca(2+) (∼0.1 mM) and becomes closer to that of the Ca-bound form in Ca2.0-buffer. This is consistent with the results of the partial specific volume and the Cotton effect around 290 nm in the CD spectra, indicating a change in the tertiary structure and less apparent change in the secondary structure of actin. The number of restrained water molecules per actin (N2) is estimated to be 1600-2100 for Ca2.0- and F-buffer and ∼2500 for Mg2.0-buffer at 10-15 °C. These numbers are comparable to those estimated from the available F-actin atomic structures as in the first water layer. The number of HMW molecules is roughly explained by the volume between the equipotential surface of -kT/2e and the first water layer of the actin surface by solving the Poisson-Boltzmann equation using UCSF Chimera.

Dielectric relaxation in isobutyl alcohol-NMP and isobutyl alcohol-DMSO mixtures studied by microwave dielectric relaxation spectroscopy

The dielectric constant for isobutyl alcohol-NMP and isobutyl alcohol-DMSO mixtures with entire concentration have been determined in the frequency range 20 MHz to 20 GHz at 298 K using the dielectric relaxation spectroscopy (DRS) method. The mixture behavior is described according to Davidson-Cole, Cole-Cole, and two Debye-type relaxation model functions whose evolution with composition is analyzed. A distinct antiparallel arrangement of dipoles is obtained for neat NMP (DMSO) in the isobutyl alcohol liquid state according to the Kirkwood correlation factor, calculated from the static permittivity.

Microwave Dielectric Relaxation of Alcohols in non polar solutions

The properties of the binary mixtures of 1-propanol and phenol have been studied at constant temperature 303K in dilute solutions of benzene using standard standing wave microwave X-band (9.4 GHz) Jband (7.4 GHz) technique. The values of different dielectric parameters e0, e', e'', e∞ have been determined for five different mole fractions of 1-propanol and phenol. The values of permittivity and dielectric loss are used to evaluate relaxation time for overall molecular rotation (τ1), relaxation time for intermolecular rotations (τ2), most probable relaxation time (τ0) and dipole moment (μ) at constant temperature 303K. The values of relaxation times and dipole moment are found to increases with the mole fraction of 1-propanol, phenol in all binary mixtures. The energy parameter (ΔFτ) for dielectric relaxation process of the mixtures is also calculated. It is found that the dielectric relaxation process can be treated as a rate process. The present investigation suggest that existence of both the intermolecular and intramolecular orientation takes place in both binary mixtures.

Microwave Dielectric Relaxation in Binary Mixtures of Pyridine and 1-Propanol at Different Temperatures

Dielectric constant (ε′) and Dielectric loss (ε″) of the binary mixtures of the pyridine and 1-propanol have been measured at microwave frequencies of X-band and J-band at 303,313 and 323K temperatures. Static dielectric permittivity (ε0) of the liquid samples has been determined using precision LCR meter. Dielectric permittivity at optical frequency (ε∞) has also been measured. Determined values of Static dielectric permittivity (ε0) and complex permittivity (ε*) at 9.1 GHz frequency were used to evaluate relaxation time (τ). Determined parameters have been interpreted in terms of molecular interaction among the molecular species of the binary mixtures.

Microwave dielectric permittivity and relaxation of aqueous potassium trimethylacetate solutions

The MW dielectric properties of aqueous potassium trimethylacetate (pivalate) solutions have been measured at six frequencies (10–25 GHz) at 288, 298, and 308 K. The static dielectric constants and dielectric relaxation times and activation parameters have been calculated. Trimethylacetate ion leads to the decrease in the mobility of water molecules and strengthening of their hydrogen bonds. These changes of water are similar to those in solutions of other carboxylates with a large number of nonpolar groups. The hydrophobic hydration of the trimethylacetate ion is maximal in this series.

Microwave Dielectric Relaxation Spectroscopy Study of Alkan-1-ol/Alkylbenzoate Binary Solvents

The structure and dynamics of alkan-1-ol/alkylbenzoate binary mixtures have been studied by microwave dielectric relaxation spectroscopy in the 200 MHz to 20 GHz frequency range. The binary mixtures of methanol, ethanol, propan-1-ol, butan-1-ol, and pentan-1-ol with methyl, ethyl, propyl, and butyl benzoates were studied at 298.15 K. The relaxational response of the pure alcohols, pure esters, and their binary mixtures over the full composition range is properly described by the Havriliak-Negami model. The alcohol content, alcohol length, and alkyl side-chain effects on the relaxational properties have been studied for these mixtures over the whole composition range. From the experimental readings, the effective and the corrective Kirkwood and Bruggeman correlation factors have been calculated. The data gathered have been interpreted in terms of the alkyl side-chain effect and their reliance on the mixture composition.

Microwave dielectric permittivity and relaxation for aqueous potassium trifluoroacetate solutions

Microwave dielectric permittivity and relaxation for aqueous potassium trifluoroacetate solutions