Polarization Relaxation Time Research Articles

On the complex conductivity signatures of calcite precipitation

Calcite is a mineral phase that frequently precipitates during subsurface remediation or geotechnical engineering processes. This precipitation can lead to changes in the overall behavior of the system, such as flow alternation and soil strengthening. Because induced calcite precipitation is typically quite variable in space and time, monitoring its distribution in the subsurface is a challenge. In this research, we conducted a laboratory column experiment to investigate the potential of complex conductivity as a mean to remotely monitor calcite precipitation. Calcite precipitation was induced in a glass bead (3 mm) packed column through abiotic mixing of CaCl2 and Na2CO3 solutions. The experiment continued for 12 days with a constant precipitation rate of ∼0.6 milimole/d. Visual observations and scanning electron microscopy imaging revealed two distinct phases of precipitation: an earlier phase dominated by well distributed, discrete precipitates and a later phase characterized by localized precipitate aggregation and associated pore clogging. Complex conductivity measurements exhibited polarization signals that were characteristic of both phases of calcite precipitation, with the precipitation volume and crystal size controlling the overall polarization magnitude and relaxation time constant. We attribute the observed responses to polarization at the electrical double layer surrounding calcite crystals. Our experiment illustrates the potential of electrical methods for characterizing the distribution and aggregation state of nonconductive minerals like calcite. Advancing our ability to quantify geochemical transformations using such noninvasive methods is expected to facilitate our understanding of complex processes associated with natural subsurface systems as well as processes induced through engineered treatments (such as environmental remediation and carbon sequestration).

Geometrical study of electrorheological activity with shape-controlled titania-coated silica nanomaterials

The titania-coated silica nanomaterials with three different shapes (nanosphere, nanorod, nanotube) are fabricated to examine the influence of particle geometry on ER fluid in nanometer-size region. The effect of particle geometry on ER activity is studied by varying the geometric aspect ratio of dispersing materials. The ER activities of titania-coated silica nanomaterials exhibit a dependence on their aspect ratio. Interestingly, the shear stress of titania-coated silica nanomaterials based ER fluids increases with increasing the aspect ratio. Geometrical study is performed to give deep insights into the primary factors that determine the ER activity. It is believed that the geometrical effect originated from high aspect ratio played a dominant role in enhancing the performance of ER fluid. Furthermore, the dielectric property analysis based on dielectric loss model clarifies that an increase in aspect ratio has been coupled with the larger achievable polarizability and short relaxation time of interfacial polarization. Consequently, the increment in aspect ratio has strong influence on ER activity, provides outstanding enhancement in shear stress value of titania-coated silica nanotube based ER fluid.

Orientation-dependent electromagnetic properties of basalt fibre/nickel core–shell heterostructures

The influence of orientation on electromagnetic properties of basalt fibre/nickel core–shell heterostructures prepared by a simple electroless plating method is investigated. For comparison, the same investigation is also performed on naked basalt fibres. For electromagnetic measurement, the directions of basalt fibre/nickel and naked basalt fibres are parallel, random and perpendicular to the direction of external electric field, termed E|| sample, random sample and E⊥ sample, respectively. Electromagnetic anisotropy can be clearly observed in the basalt fibre/nickel core–shell heterostructures, while electromagnetic properties of naked basalt fibres are unrelated to the orientation. The E⊥ basalt fibre/nickel shows the highest dielectric loss but the lowest magnetic loss, and E|| basalt fibre/nickel exhibits the highest magnetic loss but the lowest dielectric loss. The dielectric loss of E⊥ basalt fibre/nickel is several times as large as that of E|| basalt fibre/nickel, which could be attributed to the increase of polarization relaxation time as a consequence of the nanosize-confinement effect. The magnetic loss of E|| basalt fibre/nickel is even one order of magnitude higher than that of E⊥ basalt fibre/nickel, which originates mainly from the natural magnetic resonance of basalt fibre/nickel core–shell heterostructures.

Relationships between induced polarization relaxation time and hydraulic properties of sandstone

We investigated electrical and physical–chemical properties of six sandstone samples with contrasting mineralogical characteristics and with hydraulic conductivity varying in a wide range. The electrical data were obtained from time domain spectral induced polarization (IP) measurements. We inverted the IP decays to relaxation time distributions, and then compared the modal relaxation times with the dominant pore throat diameters obtained from the Mercury Injection Capillary Pressure (MICP) data. We found a positive logarithmic relationship between the relaxation time and the pore throat diameter. Also, we found the normalized chargeability (an integral IP parameter) to be positively correlated with the clay content. These two results suggest that the polarization of our sandstones is controlled by the pore throat distribution, and by the clay content. The logarithmic relationship contradicts previous theories, and is not universal. Adopting an approach of Kruschwitz and her co-workers, we calculated the effective diffusivity from IP and MICP data, and we found the effective diffusivity values ranging from 2.9 × 10−13 to 1.6 × 10−10 m2 s−1. High diffusivity values, typical of surface diffusion, were obtained for clean sandstones. Low diffusivity values were obtained for clayey sandstones, and they were one to two orders of magnitude lower than those characteristic of the surface diffusion. We proposed two mechanisms to explain the ‘slow’ diffusion: (1) the effect of surface tortuosity of pore throats filled with clay minerals and (2) the effect of pore geometry. These two effects represent an obstacle in assessing the pore throat diameter and hydraulic conductivity of sandstones with large specific surface and clay content on the basis of spectral IP measurements. However, we believe that the sandstones featuring ‘slow’ diffusion can be discriminated based on the integral polarization parameters, and that the relaxation time remains a valuable parameter for assessing hydraulic properties of clean sandstones.

Investigation of ferroelectric properties of strontium barium niobate crystals by second harmonic generation technique

The ferroelectric properties of SrxBa1 − xNb2O6 (SBN-x) crystals have been investigated using noncollinear (diffuse) second harmonic generation of IR radiation converted by a disordered domain structure. The switching characteristics have been determined from the dependences of the second harmonic intensity I2ω(t) and I2ω(E) for the SBN-0.75 crystals. These characteristics are in good agreement with the results of measurements by traditional methods and exhibit a number of specific features (long polarization relaxation times, irreproducibility of the shape of hysteresis loops, low-frequency dependence of the quantity Ec) associated with the relaxor nature of SBN solid solutions. The kinetics of the diffuse second harmonic generation can be described in the framework of the phenomenological approach to polarization relaxation processes in relaxor ferroelectrics. The intensity of the diffuse second harmonic in switching is determined by the parameters (duration, amplitude) of the switching field pulse.

The effects of temperature and frequency on the dielectric properties, electromagnetic interference shielding and microwave-absorption of short carbon fiber/silica composites

The dielectric spectroscopy of short carbon fiber/silica composite in the frequency range from 8.2 to 12.4 GHz at temperatures between 30 and 600 °C has been performed. The composite was prepared by conventional ceramic processing. The real part of the permittivity increases with increasing temperature, which is attributed to the shortened relaxation time of electron polarization, and the imaginary part also increases which is ascribed to the increasing electrical conductivity of the carbon fibers. The effect of frequency is found in reflection coefficient and absorption coefficient, and the corresponding mechanisms for the effect are proposed. Results indicate that the composite has good electromagnetic interference shielding property. By calculating the microwave-absorption as a single-layer absorber, we find that the reflection loss varies with the changes of thickness and temperature, due to the deviation of impedance matching condition.

High dielectric loss and its monotonic dependence of conducting-dominated multiwalled carbon nanotubes/silica nanocomposite on temperature ranging from 373 to 873 K in X-band

The dielectric properties of multiwalled carbon nanotubes/silica (MWNTs/SiO2) nanocomposite with 10 wt % MWNTs are investigated in the temperature range of 373–873 K at frequencies between 8.2 and 12.4 GHz (X-band). MWNTs/SiO2 exhibits a high dielectric loss and a positive temperature coefficient (PTC) of dielectric effect that complex permittivity increases monotonically with increasing temperature. The PTC effect on the dielectric constant is ascribed to the decreased relaxation time of interface charge polarization, and the PTC effect on the dielectric loss is mainly attributed to the increasing electrical conductivity. The loss tangent strongly supports the dominating contribution of conductance to the dielectric loss.

Time-resolved dielectric investigation of relaxation kinetics in metastable caffeine

Using time-resolved dielectric relaxation spectroscopy, we have studied the kinetics of the first-order phase transformation of caffeine from its high temperature rotational solid form to the room temperature phase. The results indicate that the kinetics can be fitted by a highly stretched exponential law. The kinetics, thus, differ from that of a ‘typical’ nucleation and growth process. This unusual non-sigmoïdal evolution can be understood as being dominated by slow nucleation in grains with a dispersion of their size ranging below the characteristic dimension of the nucleation and growth process. The relaxation times of polarization are characterized by an activation energy closely correlated with that of the nucleation process.

Dielectric spectroscopy of hydrophilic polymers–montmorillonite clay nanocomposite aqueous colloidal suspension

Frequency-dependent complex dielectric function, loss tangent, electric modulus, alternating current electrical conductivity, and impedance spectra of poly(vinyl alcohol) (PVA), poly(vinyl pyrrolidone) (PVP), poly(ethylene glycol) (PEG), and blends of PVA–PVP and PVA–PEG, loaded with polymer grade montmorillonite (MMT) clay upto 5 wt% of solute (polymer + clay) in aqueous colloidal suspensions, have been investigated in the frequency range 20 Hz to 1 MHz at 27 °C. These materials show the dielectric dispersion corresponding to ionic conduction and electrode polarization phenomena in the experimental frequency range. The loss tangent peak frequency which separates the contribution of the bulk material and the electrode polarization phenomenon was used to evaluate the electrode polarization relaxation time corresponding to the dynamics of electric double layers. The dielectric and electrical conductivity spectra were interpreted as a result of these material complex structures formed by constituents H-bonding interactions, and the clay intercalation and exfoliation that alter the conduction pathways. Results show that the dielectric/electrical properties of the polymer–clay nanocomposites aqueous colloidal suspension have good resemblance to their structural properties, which were explored from other spectroscopic and morphological techniques. A close look on the dielectric parameters of the investigated materials proves the suitability for the synthesis of new materials with desirable and predicted properties.

Exciton broadening and spin dynamics in III-V/II-VI:Mn heterovalent double quantum wells

We report on the optical studies of exciton broadening mechanisms and exciton spin dynamics in diluted magnetic semiconductor GaAs/AlGaAs/ZnSe/ZnCdMnSe heterovalent double quantum wells (QWs) grown by molecular-beam epitaxy. The heterovalent interface manifests itself in the fluctuations of the interface dipole moment and, hence, in an enhanced inhomogeneous broadening of the excitonic emission, as well as in generation of type-II localized excitons. Microphotoluminescence measurements indicate that these fluctuations occur on the scale less than $1\text{ }\ensuremath{\mu}\text{m}$. The rise curves of circular polarization of the excitonic emission are measured in an external magnetic field. The kinetics of the exciton spin polarization is strongly affected by the strength of electronic coupling between the GaAs/AlGaAs and ZnSe/ZnCdMnSe QWs, as well as by the factor of the exciton inhomogeneous broadening. Depending on these parameters, the relaxation time of the net spin polarization in the structures varies from the values shorter than 20 ps up to $\ensuremath{\sim}9\text{ }\text{ns}$.

Characterization of solvent effect on low-frequency dielectric dispersion and relaxation behaviour of ethylene glycol oligomers

The complex relative dielectric function ɛ⁎( ω) = ɛ′ − jɛ″, electric modulus M⁎( ω) = M′ + jM″, alternating current electrical conductivity, and loss tangent tan δ = ɛ″ / ɛ′ spectra of binary mixture of ethylene glycol oligomers (EGOs) namely, ethylene glycol (EG), diethylene glycol (DEG) and poly(ethylene glycol)s (PEGs) of average molecular weight 200, 300, 400 and 600 g mol − 1 with water (W), ethyl alcohol (EA) and 1,4-dioxane (Dx) in the frequency range 20 Hz to 1 MHz were investigated at 298 K. In the lower-frequency range, the EGOs + W, EGOs + EA and EGOs + Dx mixtures show the direct current conductivity behaviour, and their values can be monitored by concentration variation of the mixture constituents, specially in case of EGOs + W and EGOs + Dx mixtures. The frequency value corresponding to tan δ peak, separates the contribution of the bulk and the electrode polarization phenomena, which is used to evaluate the electrode polarization relaxation time. The M″( f) peak frequency value is considered to evaluate the ionic conduction relaxation time. In these binary mixtures, as compared to rigid chain EG and DEG molecules, the flexible chain EGOs of higher molecular weight have significantly different dielectric response.

The Dipole Moment and Molecular Mobility of Cholesteryl-Containing Monomers in Solution: Association and Gel Formation

The permittivity, molecular dipole moment, and dielectric relaxation parameters (relaxation time and activation energy) of cholesteryl esters of alkyl-, methacryloyl-ω-oxy-, and aminocarboxylic acids were studied in dilute solutions in toluene. The influence of the chemical structure of molecules on these characteristics was considered. The presence of NH groups and cholesteryl radicals (responsible for H-bonding and specific dispersion interactions) and an increase in the length of methylene chains in molecules substantially influenced dipole moments and dipole polarization relaxation times and contributed to the development of structuring processes (association and gel formation) in solutions of these compounds.

Electro-optic search for critical divergence of the charge-density-wave diffusion constant at the onset of depinning

We have used electroreflectance measurements to study charge-density-wave (CDW) polarization dynamics at voltages near the CDW depinning onset $({V}_{\mathrm{on}})$ in the quasi-one-dimensional conductor ${\mathrm{K}}_{0.3}\mathrm{Mo}{\mathrm{O}}_{3}$ (``blue bronze''). For low voltages, where the phase-slip rate is low, it is expected that the polarization relaxation time should be inversely proportional to the CDW diffusion constant, which is expected to diverge at ${V}_{\mathrm{on}}$. At $T=78\phantom{\rule{0.3em}{0ex}}\mathrm{K}$, we observe saturation of the relaxation time at low voltages, suggesting that we are in the low phase-slip limit and allowing us to estimate the noncritical value of the CDW diffusion constant $\mathrm{D}(\ensuremath{\infty})\ensuremath{\sim}0.02\phantom{\rule{0.3em}{0ex}}{\mathrm{cm}}^{2}∕\mathrm{s}$, consistent with the measured phason velocity. At other temperatures, the relaxation time increases with decreasing voltage even at the lowest voltages we could measure. In no case do we observe the expected ``critical speeding up,'' setting an upper limit on the critical region of ${\ensuremath{\mid}V∕{V}_{\mathrm{on}}\ensuremath{-}1\ensuremath{\mid}}_{\text{critical}}l0.06$.

Dielectric relaxation and phase transitions at cryogenic temperatures in0.65[Pb(Ni1∕3Nb2∕3)O3]−0.35PbTiO3ceramics

Dielectric measurements on $0.65[\mathrm{Pb}({\mathrm{Ni}}_{1∕3}{\mathrm{Nb}}_{2∕3}){\mathrm{O}}_{3}]\ensuremath{-}0.35\mathrm{Pb}\mathrm{Ti}{\mathrm{O}}_{3}$ ceramic in the temperature range $90--470\phantom{\rule{0.3em}{0ex}}\mathrm{K}$ show a relaxor ferroelectric transition around $350\phantom{\rule{0.3em}{0ex}}\mathrm{K}$ with a Vogel-Fulcher freezing temperature of $338\phantom{\rule{0.3em}{0ex}}\mathrm{K}$ and an appearance of a nonergodic relaxor ferroelectric phase of tetragonal structure at room temperature. This nonergodic phase reenters into the relaxor state at low temperatures as evidenced by the appearance of a frequency dependent anomaly in the imaginary part of the dielectric constant around $160\phantom{\rule{0.3em}{0ex}}\mathrm{K}$, similar to those reported in other relaxor ferroelectric based morphotropic phase boundary ceramics. The polarization relaxation time for the $160\phantom{\rule{0.3em}{0ex}}\mathrm{K}$ anomaly also follows Vogel-Fulcher type temperature dependence. Temperature dependent magnetization measurements show that this low temperature anomaly is not linked with any magnetic transition. Elastic modulus and low temperature x-ray diffraction measurements reveal a tetragonal to monoclinic phase transition around $225\phantom{\rule{0.3em}{0ex}}\mathrm{K}$. It is argued that the low temperature dielectric dispersion around $160\phantom{\rule{0.3em}{0ex}}\mathrm{K}$ results from the freezing of mesoscopic conformally miniaturized monoclinic domains formed inside the parent tetragonal domains below the structural phase transition temperature of $225\phantom{\rule{0.3em}{0ex}}\mathrm{K}$.

Dielectric polarization evolution equations and relaxation times

In this paper we develop dielectric polarization evolution equations, and the resulting frequency-domain expressions, and relationships for the resulting frequency dependent relaxation times. The model is based on a previously developed equation that was derived using statistical-mechanical theory. We extract relaxation times from dielectric data and give illustrative examples for the harmonic oscillator and derive expressions for the frequency-dependent relaxation times and a time-domain integrodifferential equation for the Cole-Davidson model.

Experimental study of induced polarization relaxation time spectra of shaly sands

The induced polarization decay curve contains much more information than chargeability which is often used in traditional induced polarization logging tool. The singular value decomposition algorithm makes it possible to transform induced polarization decay data into relaxation time spectrum. The spectrum logging tool can be used as an in-situ method to estimate pore structure, permeability, formation water resistivity and shaliness of reservoir with deep investigation depth and high signal-to-noise ratio. In order to use this new logging method in practice, effect of some factors on the relaxation time spectrum should be investigated. The induced polarization decay curve measurements have been performed on seven samples from Daqing Oil Field using a four-electrode technique. The effects of temperature, overburden pressure, electrolyte and salinity on the relaxation spectra of the core samples were analyzed qualitatively. When we discussed the effect of one parameter on the spectra, the others were fixed. The results show that the spectra shift to low time constants with temperature increasing, but the shape is almost the same. The temperature dependence of the spectrum can be corrected. When the overburden pressure increases, the relative amplitudes of low relaxation time constants are the same, and those of high constants decrease. When pressure is diminished again, the amplitudes of high time constants do not recover to the original distribution. The salinity has small influence on the spectra. The electrolyte has the influence on the spectra because of the diffusion coefficient different. This influence of electrolyte can also be corrected.

Electromagnetic properties of polyaniline/maghemite nanocomposites: I. The effect of re-doping time on the electromagnetic properties

This article is to carry out researches on the synthesis of the polyaniline/γ-Fe 2O 3 nanocomposites by a reverse micelle process and the effects of re-doping time on the electromagnetic properties of polyaniline/γ-Fe 2O 3 nanocomposites, investigated by Fourier transform spectrometer (FT-IR), X-ray photoelectron spectroscopy (XPS), wide angle X-ray diffraction diffractometer (WAXD), impedance analyzer, micro-ohmeter, and superconductor quantum interference device (SQUID). The nanostructure of the polyaniline/γ-Fe 2O 3 nanocomposites was characterized by micrographs of transmission electron microscopy (TEM). It was found that the dispersed γ-Fe 2O 3 phase is roughly distributed in the polyaniline matrix. Results showed that, in the presence of γ-Fe 2O 3, the growth rate of quinoid ring is markedly retarded. The crystallinity and doping level of polyaniline in the nanocomposites increase with re-doping time, the conductivity and dielectric properties (i.e., permittivity and loss factor) of nanocomposites are hence increased and the ionic polarization relaxation time become shorter from 1.71 × 10 −9 to 7.48 × 10 −10 s. The particle size and γ-Fe 2O 3 content in the nanocomposites decrease with re-doping time due to the reduction effect resulting from the doped protonic acid of polyaniline. For the room-temperature SQUID analysis, the superparamagnetic behavior is observed, suggesting the presence of the thermal activation energy contribution to the magnetic moment. The saturated magnetization was decreased with decreasing γ-Fe 2O 3 contents.

Electrical and dynamooptical properties of Frechet dendron-modified polystyrene molecules in solutions

The electrooptical, dynamic, and dielectric characteristics of polystyrene modified by the Frechet dendrons of 1–4 generations have been studied in benzene, chloroform, and THF solutions. It has been shown that the Kerr constant and the shear optical coefficient for all the studied polymers coincide in sign and their absolute values increase with the dendron generation number. The intrinsic optical anisotropy of the repeating unit of dendronized polystyrene molecules is negative in sign, and its absolute value tends to grow with an increase in the generation number of dendrons. The frequency dispersions of the Kerr constand and of the dielectric polarization have been discovered for solutions of the modified polymer. The ratio between the times of relaxation characterizing the dispersion of dielectric permittivity and of the Kerr constant of solutions and the times of a rise and decay of electric birefringence measured on the onset and termination of the rectangular-pulsed field does not obey the longitudinal relaxation theory for polar macromolecules. The relaxation times of dielectric polarization and of electric birefringence tend to increase with the dendron generation number.

Multi-Exponential Inversion and Laboratory Study of Induced Polarization Relaxation Time Spectra of Shaly Sands

Abstract According to the traditional Induced Polarization (IP) logging method, the IP relaxation time spectrum can give much more information about a reservoir, such as the pore structure, permeability, formation water resistivity, and shaliness. In this paper, the Singular Value Decomposition (SVD) algorithm is used to inverse the IP multi-relaxation data of the rock samples. The appropriate number of relaxation arrangement points in the relaxation data inversion is from 32 to 64. All of the relaxation spectra show a multi-peak shape. IP decay curve measurements have been performed on 30 samples from the Daqing Oil Field using the four-electrode technique. The effects of charging current, charging and discharging time, brine salinity, and water saturation on the relaxation spectra of the rock were analyzed qualitatively, so that we could develop a new IP spectra logging tool that could be used successfully in practice. When we discussed the effect of one parameter on the relaxation time spectra, the others remained fixed. The results show that the relaxation spectrum relates with the charging time, discharging time, and depends strongly on water saturation. The salinity of NaCl brine and the charging current density are shown to have a small influence on the relaxation spectra in the special ranges. Introduction Induced polarization (IP) phenomena were observed more than 80 years ago, which may be caused by metallic minerals or clay Content(1–8). The detection of IP in the time-domain is made by measuring both the maximum voltage during the charging period of a dc current flow, and the transient decay of the electrical potential as a function of time, after the current is turned off. IP logging is traditionally used to determine the formation water resistivity and shaliness parameter (Qv), which is defined as the cation exchange capacity of the shaly sands per unit pore volume(9–12). But up to now, no IP logging has successfully been used commercially to evaluate or locate petroleum reservoirs. The theory analysis shows that the IP relaxation characteristics relate to the pore structure of the rock and the IP decay curve is a superposition of signals coming from all pores with different sizes(13). So, the curve can be fitted with multi-exponential decay function and a relaxation spectrum can be obtained. The spectrum contains much more information than the traditional IP method. The IP spectra of full water-saturated rock gives a quick, easy, and nondestructive way to characterize the rock, such as the pore structure, permeability, and Qv. On the other hand, we can develop a new time-domain IP spectra logging tool. This kind of IP spectra logging can be also used to obtain the formation water resistivity and shaliness parameter, Qv, as the traditional time-domain IP logging tool. In order to transfer the lab results downhole, the borehole effects, such as rugosity and mud, should also be considered. This can be achieved by using focusing technology as well as technologies used in traditional lateral logging tools.

Thermodynamic approach to obtaining a highly spin-polarized strongly correlated Fermi liquid in solid-state systems

We present a thermodynamic approach to obtain a highly polarized heavy Fermi liquid in solid-state systems. It is similar to that proposed by Castaing and Nozi\`eres [J. Phys. (Paris) 40, 257 (1979)] for polarizing liquid $^{3}\mathrm{He}$. The mechanism applies to a class of materials where local moments coexist with a Fermi liquid at a first-order transition. Fast melting of the magnetic field aligned local moment phase, due to a change of pressure or magnetic field, yields a highly polarized Fermi liquid state. This fast melting implies that the relaxation time of the spin polarization is long compared to the melting time of the local moment phase. We discuss the conditions for attaining it in the materials considered.