Dielectric Loss Modulus Research Articles

Porous chitosan particles doped by in situ formed silver nanoparticles: Electrorheological response in silicon oil

AbstractEffect of in situ formed silver nanoparticles doping on electrorheological response of highly porous chitosan particles in suspensions of polydimethylsiloxane (silicone oil) is considered. Silver nanoparticles are directly reduced by chitosan from solution. Highly porous chitosan particles with different silver content are fabricated by spraying from solution followed by freeze‐drying. A high and stable electrorheological response of suspensions in wide range of electric field strength is observed at a very low filler content of 1 wt%. The nature of the electrorheological effect is considered from the standpoint of dielectric spectroscopy. The activation energies of polarization processes are determined from the temperature dependences of the dielectric loss modulus. The study shows the opportunity to control the properties of stimuli‐responsive materials by changing the structure and physicochemical properties of the functional filler. This approach opens up new possibilities for creating materials with high performance and predetermined properties.

The size effect of faceted detonation nanodiamond particles on electrorheological behavior of suspensions in mineral oil

Suspensions of hydrogenated detonation nanodiamond (DND) particles in mineral oil are electrorheological fluids: their viscosity and yield stress increase under an electric field. The effect of the initial DND particles size obtained during the explosion on the properties of low-filled (up to 4 wt%) electrorheological fluids was considered. The small-angle X-ray scattering method revealed the differences in the structural organization of DNDs with sizes of 3 and 5 nm in a mineral oil, which affects the sedimentation stability of suspensions and their electrorheological behavior. The sedimentation ratio and the values of the yield stress are lower for 3 nm particles suspensions in the whole studied electric field strength (0–6 kV/mm). The method of impedance dielectric spectroscopy showed the differences in the electrophysical characteristics of suspensions filled with particles of 3 and 5 nm. The activation energies of polarization processes were estimated from the temperature dependences of the dielectric loss modulus. The study shows the key role of filler size for creating high performance electrosensitive materials and hypothesizes the reasons for different properties of electrorheological fluids filled by 3 and 5 nm DND particles.

On the dynamic behavior of a functionally graded viscoelastic-piezoelectric composite substrate subjected to a moving line load

The present study bestows the analytical investigation of incremental mechanical stresses (compressive stress, shear, and tensile) and electrical displacements (vertical and horizontal components) induced due to a moving line load on an irregular transversely isotropic functionally graded viscoelastic-piezoelectric material (FGVPM) substrate. The closed form expressions of said induced mechanical stresses and induced electrical displacements are deduced and validated with pre-established results for electrically open and short conditions. The elastic moduli (stiffness tensors), piezoelectric moduli, dielectric moduli, elastic loss moduli, piezoelectric loss moduli, and dielectric loss moduli for a viscoelastic-piezoelectric composite are computed and used for numerical computation and graphical demonstration. The effectuality of diverse physical parameters (viz. maximum depth of irregularity, friction due to rough upper surface, functional gradient parameter, irregularity factor associated with different types of irregularity viz. rectangular irregularity, parabolic irregularity and no irregularity) on said induced stresses and electrical displacements in the aforementioned composite substrate has also been discussed. A comparative analysis has also been made to examine the impact of piezoelectricity and viscoelasticity on theon said induced mechanical stresses and induced electrical displacements. In particular, some special peculiarities are also sketched by means of graphs.

Love-type waves in a piezoelectric-viscoelastic bimaterial composite structure due to an impulsive point source

The analysis of wave propagation phenomenon piezoelectric-viscoelastic composites still remains an unexplored field of research. The usage of a passive polymer (Epoxy) with active piezoelectric ceramic causes viscoelasticity in the piezoelectric material which results into a piezoelectric-viscoelastic composite. The present study aims to analyze the propagation behavior of Love-type wave in an exponentially graded piezoelectric-viscoelastic material (EGPVM) stratum lying over a functionally graded piezoelectric-viscoelastic material (FGPVM) substrate due to an impulsive point source at its interfacial surface. The electro-visco-mechanical field equations are laid down for the piezoelectric-viscoelastic medium. The analytical solution procedure involves the use of suitable Green's function and admissible boundary conditions. The established frequency equation is in complex form; of which the real expression imparts the frequency curve and imaginary expression gives the attenuation curve of Love-type wave. To depict the results numerically, two distinct piezoelectric-viscoelastic materials (Epoxy-BNKLBT and Epoxy-KNLNTS ceramics) for EGPVM stratum and FGPVM substrate are taken into account. The phase velocity profile and attenuation coefficient profile of Love-type wave is portrayed graphically. Diagnostic results are simulated numerically which forefronts the effect of distinct parameters. The study manifests the impact of the material medium parameters, viz. piezoelectric constants, dielectric constants, piezoelectric loss moduli, dielectric loss moduli, exponential gradient parameter and magnifying gradient parameters on the phase velocity and attenuation coefficient of Love-type wave. For sake of validation, the obtained results are matched with the classical one, as a special case of the problem. The outcomes of the study may find its worth in better and optimum design of surface acoustic wave devices and Love wave sensors, keeping efficiency at its premium.

Effect of nanosilica on optical, electric modulus and AC conductivity of polyvinyl alcohol/polyaniline films

Nanosilica (NS) was synthesized by a sol–gel method and mixed with 0.98 polyvinyl alcohol (PVA)/0.02 polyaniline (PANI) in different amounts to produce nanocomposite films. High-resolution transmission electron microscopy (HR-TEM) revealed the average particle size of the NS to be ca. 15nm. Scanning electron microscopy (SEM) showed that the NS was well-dispersed on the surface of the PVA/PNAI films. The Fourier transform infrared (FTIR) spectra of the samples showed a significant change in the intensity of the characteristic peak of the functional groups in the composite films with the amount of NS added. The absorbance and refractive index (n) of the composites were studied in the UV–vis range, and the optical energy band gap, Eg, and different optical parameters were calculated. The dielectric loss modulus, M″ and ac conductivity, σac, of the samples were studied within 300–425K and 0.1kHz–5MHz, respectively. Two relaxation peaks were observed in the frequency dependence of the dielectric loss modulus, M″. The behavior of σac(f) for the composite films indicated that the conduction mechanism was correlated barrier hopping (CBH). The results of this work are discussed and compared with those of previous studies of similar composites.

Alternating current conductivity and dielectric relaxation of PANI:PVDF composites

In this work, PANI:PVDF composites films were prepared with different PANI contents (p = 1, 2, 3, 4 and 5%). The resulting films were dried at various temperatures such as 30, 90 and 120 °C. The alternating current mechanisms and dielectric relaxation and of PANI:PVDF films were studied using complex impedance spectroscopy over a wide range of temperature (303–453 K) and a frequency range (1 kHz to 1 MHz). We found that the ac conductivity in PANI:PVDF composite is governed by correlated barrier hopping (CBH) model. In dielectric loss modulus study, two relaxation processes were identified. The first peak was associated to Maxwell Wagner-Sillas (MWS) relaxation whereas the second one which obtained at higher frequency was attributed to the αc relaxation. For PANI:PVDF film which dried at 30 °C, the MWS relaxation appears only at higher temperature. The temperature dependence of αc relaxation was suitably fitted according to Vogel Flucher Temman model whereas MWS relaxation follows Arrhenius type behavior. The effect of drying temperature on microstructure and phase crystallization of PVDF in the composites was carried out using atomic force microscopy (AFM) and Fourier transform infrared (FTIR) spectroscopy. These results were used to find a reasonable correlation between microstructure and electrical properties.

Dielectric relaxation and optical properties of polyvinyl chloride/lead monoxide nanocomposites

Sol–gel synthesized lead monoxide (PbO) nanoparticles were mixed with polyvinyl chloride (PVC). The dielectric characteristics of PVC/PbO nancomposite films were studied in the temperature range 303–408 K and frequency range 30 kHz–3 MHz. There is a sharp increase in the dielectric constant (e′), after the glass transition temperature. According to the temperature and frequency dependence of the dielectric loss modulus (M″), the observed αa-relaxation peak is due to the micro-Brownian motion of the polymer main chains. The behavior of σac (f) for the composite films indicate that the homogenous distribution of PbO nanoparticles allows the formation of conductive three-dimensional networks throughout the nanocomposite films which assisting the charge carriers to hop from conducting clusters to neighbors. The influences of PbO content on the direct optical band gap and the refractive index of the films are also discussed and compared with those of previous studies of PVC composites. POLYM. COMPOS., 34:2031–2039, 2013. © 2013 Society of Plastics Engineers

Influence of Cr2O3 nanoparticles on the physical properties of polyvinyl alcohol

Nano-sized chromium oxide (Cr2O3) was synthesized by sol-gel method and mixed with polyvinyl alcohol (PVA) to produce nanocomposite films. Scanning electron microscopy (SEM) was used to observe the morphology and dispersion of Cr2O3 on the surface of the PVA films. X-ray diffraction (XRD) was performed on nano-sized Cr2O3, pure PVA, and Cr2O3/PVA composites. Based on the results of both XRD and high-resolution transmission electron microscopy (HR-TEM), the average particle size of the Cr2O3 was ≈ 46 nm. Differential scanning calorimetry (DSC) showed that the thermal stability and degree of crystallinity of the PVA were reinforced by the addition of Cr2O3 nanoparticles. The absorbance and extinction coefficients of the composites were studied in the UV-vis range and compared with those of pure PVA. The optical energy band gap, Eg, was calculated. Dielectric constant, ε′, dielectric loss modulus, M″, and ac conductivity, σac, of all samples were measured within temperature and frequency ranges of 300–468 K and 10 kHz-2 MHz, respectively. According to the frequency and temperature dependence of the dielectric loss modulus, M″, the observed α-relaxation peak was due to the micro-Brownian motion of the polymer main chains. The behavior of σac(f) for the composite films indicated that the conduction mechanism was correlated barrier hopping (CBH). The results of this work were discussed and compared with those of previous studies of PVA composites.

An alternative dielectric model for low and high frequencies: A non-equilibrium thermodynamic approach

In this paper a model for dielectric material in the formalism of Kluitenberg's theory on dielectric relaxation phenomena is proposed. The aim of the paper is to suggest a thermodynamic model with internal variable for dielectric isotropic material; in particular, by introducing the reciprocal complex dielectric susceptibility, expressions will be proposed for the dielectric storage modulus and dielectric loss modulus in cases of low and high frequencies. Finally, an expression for the reciprocal of complex susceptibility allows us to compare the results obtained with experimental data in the case of low frequencies.

An alternative dielectric model for low and high frequencies: A non-equilibrium thermodynamic approach

In this paper a model for dielectric material in the formalism of Kluitenberg's theory on dielectric relaxation phenomena is proposed. The aim of the paper is to suggest a thermodynamic model with internal variable for dielectric isotropic material; in particular, by introducing the reciprocal complex dielectric susceptibility, expressions will be proposed for the dielectric storage modulus and dielectric loss modulus in cases of low and high frequencies. Finally, an expression for the reciprocal of complex susceptibility allows us to compare the results obtained with experimental data in the case of low frequencies.

Frequency dependent conductivity studies on PMMA–LiCF3SO3 polymer electrolytes

Polymer electrolytes composed of poly(methylmethacrylate) as a host polymer and lithium triflate as a salt have been prepared by solution cast technique. Polymer salt complexation has been confirmed by attenuated total reflectance Fourier transform infrared spectral studies. The ac conductivity as a function of temperatures in the frequency range 100 Hz–1 MHz has been carried out. The conductivity–temperature plots found follows the Arrhenius rule. The complex permittivity ϵ* and complex electric modulus M* have been analysed. The dispersion observe at low frequency is due to the space charge effect arising from the electrodes. The modulus spectra reveal that the dispersion deviates from the Debye behaviour. The ionic conductivity relaxation is determined from the maximum of the peaks of the dielectric loss modulus associated with the ac activation energy for ion relaxation Efp=0·337 eV, which agrees well with the dc conduction activation energy EA=0·341 eV. Thus, it is suggested that the dynamic mechanism for the ionic conduction is achieved at the same energy barrier while conducting as well as relaxing.

Comparison of analysis of dielectric spectra of PCL in the ε∗ and the M∗ formalism

The complex dielectric modulus, M∗(ω, T), for poly(ε-caprolactone) has been obtained by inverting the complex dielectric permittivity data, ε∗(ω, T) recorded in a wide temperature and frequency range. The analysis of the dielectric loss modulus spectra M″(ω, T) have been performed by using a simulated annealing Monte Carlo procedure in order to extract the relaxation parameters for each relaxation mode. Besides the local modes γ and β, the segmental α mode associated to the glass transition, the conductivity and the interfacial polarization peaks could be analyzed with a better precision than by using the conventional non-linear least squares method in ε″ domain. The merging of the α and β modes at high temperatures is much better defined due to the less significant contribution of the ionic conductivity in M∗ formalism.