Loss Tangent Measurements Research Articles

Measuring the loss tangent of polymer materials with atomic force microscopy based methods

Atomic force microscopy (AFM) quantitatively maps viscoelastic parameters of polymers on the nanoscale by several methods. The loss tangent, the ratio between dissipated and stored energy, was measured on a blend of thermoplastic polymer materials by a dynamic contact method, contact resonance, and by a recently developed loss tangent measurement by amplitude modulation AFM. Contact resonance measurements were performed both with dual AC resonance tracking and band excitation (BE), allowing for a reference-free measurement of the loss tangent. Amplitude modulation AFM was performed where a recent interpretation of the phase signal under certain operating conditions allows for the loss tangent to be calculated. The loss tangent measurements were compared with values expected from time–temperature superposed frequency-dependent dynamical mechanical curves of materials and reveal that the loss tangents determined from the BE contact resonance method provide the most accurate values.

Effect of Syntesis and Frequency on Electrical Properties on Dielectric Ceramics MgCO<sub>3</sub>-TiO<sub>2</sub>

Magnesium titanate based dielectric materials are used for producing type-I capacitors. A common way of obtaining this material is a solid-state reaction. The process of sintering can be enhanced if mechanical activation preceedes. In this work starting powders of magnesium carbonate (MgCO3) and titanium dioxide (TiO2) with a rutile crystal modification were weighed to attain a 1:1 molar MgCO3:TiO2. Mechanical activation of the starting mixture was performed by high energy ball milling using ZrO balls and vessels with ball to powder mass ratio 40:1. The observed grinding times were 15, 30, 60 and 120 minutes. The isothermal sintering of compacted powders was conducted at 1100°C during 30, 60 and 180 minutes. For specimens synthesized in such a manner, microwave dielectric properties were measured, quality factor Q and the dielectric constant (εr) in function of frequency. The measurements of electrical resistivity, capacitance and loss tangent of samples were measured in the frequency range from 500 Hz to 5 MHz frequencies with a HIOKI 3532-50 LCR HiTESTER device at a constant voltage mode (amplitude 0.5 V of sinusoidal signal applied to the specimens).

Temperature dependent loss tangent measurement of polymers with contact resonance atomic force microscopy

The loss tangent of individual components in a blend of polypropylene (PP) and polystyrene (PS) is measured as a function of temperature with contact resonance atomic force microscopy. The loss tangent is calculated directly from the experimentally obtained contact resonance frequency, cantilever quality factor and other operating parameters. The temperature dependent variation of the loss tangent, measured at the high frequency of AFM measurements, shows peaks at different temperatures for the different polymer materials. The loss tangent peak at approximately 53 °C for PP is identified as an alpha peak signifying crystal relaxation while the loss tangent peak at approximately 75 °C for PS is identified as a glass transition.

Influence of temperature and fiber structure on the dielectric properties of polypropylene fibrous structures

In this work, dielectric spectroscopy was conducted on five commercial woven polypropylene-based fabrics. Measurements of dielectric loss tangent, the effective relative dielectric permeability and ac electrical conductivity were performed over a wide range of temperature and frequency. The results in temperature range from 250 K to 355 K showed that the samples with lower value of volume fraction whose yarn is made from a short fiber have a lower value of the above mentioned dielectric parameters than the samples with bigger value of volume fraction and filament yarn along the weft and the warp lines. Based on the results gained from the measurements in the vacuum and ambient conditions, it can be concluded that the samples with a lower value of volume fraction, whose yarn is made from a short fiber, showed stability of dielectric properties in the measurement interval. Copyright © 2014 John Wiley & Sons, Ltd.

Measurement of Viscoelastic Loss Tangent with Contact Resonance Modes of Atomic Force Microscopy

We show how atomic force microscopy techniques based on contact resonance (CR) can be used to measure the viscoelastic loss tangent tan δ of polymeric materials. The method does not require intermediate calculation of loss and storage moduli, calibration measurements, or use of the conventional CR tip shape parameter. We present the method’s physical concepts and sensitivity calculations for typical experimental parameters. In addition, CR experiments were performed on four homogeneous polymer samples (polystyrene, high-density polyethylene, and two commercial photostress polymers) with tan δ in the range from approximately 0.02 to 0.2. Results compare favorably to those obtained by microscale dynamic nanoindentation and macroscale dynamic mechanical analysis. These results show the potential of CR modes for nanoscale viscoelastic measurements of polymers and biomaterials.

Hydrodynamic corrections to contact resonance atomic force microscopy measurements of viscoelastic loss tangent

We present a method to improve accuracy in measurements of nanoscale viscoelastic material properties with contact resonance atomic force microscope methods. Through the use of the two-dimensional hydrodynamic function, we obtain a more precise estimate of the fluid damping experienced by the cantilever-sample system in contact resonance experiments, leading to more accurate values for the tip-sample damping and related material properties. Specifically, we consider the damping and added mass effects generated by both the proximity of the cantilever to the sample surface and the frequency dependence on the hydrodynamic loading of the system. The theoretical correction method is implemented on experimental contact resonance measurements. The measurements are taken on a thin polystyrene film and are used to determine the viscoelastic loss tangent, tan δ, of the material. The magnitude of the corrections become significant on materials with low tan δ (<0.1) and are especially important for measurements made with the first flexural mode of vibration.

Magnetic, Dielectric and Electrical Properties of Lithium-Magnesium Ferrites

A series of polycrystalline spinel type ferrites with composition Li x Mg0.5Ni0.5– 2 x Fe2+ x O4, where x = 0.00 to 0.25 in steps of 0.05, have been prepared by standard double sintering method sintered at temperature 1200 °C in air for 6 hours. In this work, investigations have been carried out by the measurements of X-ray diffraction (XRD), Curie temperature, permeability, loss tangent, Q-factor, dielectric constant and ac electrical resistivity of the samples. Some measurements have been done at room temperature while other measurements have been done as a function of temperature and as a function of frequency in the range from 1 kHz to 500 kHz. Curie temperature, the real part of initial permeability (μ i ), the loss tangent (tan δ), and the Q-factor have been found to be decreased with the increase of Ni-content of Li x Mg0.5Ni0.5– 2 x Fe2+ x O4 ferrites. The frequency characteristic of dielectric constant and AC resistivity decreases with the increase in frequency and increases with the increase in Ni-content.

Electrical Prope Rties of Popcorn Grains

Abstract This work contains the results of measuring the electrical properties of popcorn grains. Interest in electrical properties of biological materials resulted in engineering research in this field. The results of measurements are used for determining the moisture content, the surface level of liquid and grainy materials, for controlling the presence of pests in grain storage, for a quantitative determination of mechanical damage, in applications of dielectric heating, and in many other cases. Electrical measurements on these materials are of fundamental importance in relation to the analysis of quantity of absorbed water and dielectric heating characteristics. It is a well-known fact that electrical properties of materials, namely dielectric constant and conductivity, are affected by the moisture content of material. This fact is important for the design of many commercial moisture-testing instruments for agricultural products. The knowledge of dielectric properties of materials is necessary for the application of dielectric heating. The aim of this work was to perform the measurements of conductivity, dielectric constant and loss tangent on samples of popcorn grains, the electrical properties of which had not been sufficiently measured. Measurements were performed under variable moisture content and the frequency of electric field in the range from 1 MHz to 16 MHz, using a Q meter with a coaxial probe. It was concluded that conductivity, dielectric constant and loss tangent increased with increase of moisture content, and dielectric constant and loss factor decreased as the frequency of electric field increased.

Influence of Ni2+ substitution on the structural, dielectric and magnetic properties of Cu–Cd ferrite nanoparticles

Nanoparticles with compositions of Cu0.4−0.5xCd0.2Ni0.4+xFe2−0.5xO4 (0.0⩽x⩽0.5) were successfully synthesized by a citrate–nitrate sol–gel auto combustion route. The combusted powder was calcinated at four hours in a furnace and then slowly cooled to room temperature. The analysis methods of FTIR, XRD, FESEM, VSM and dielectric measurements were used to characterize prepared magnetic particles. The effect of Ni2+ substitution on structural, magnetic and dielectric properties of Cu–Cd ferrite nanoparticles was studied. The comprehensive studies on compositional and frequency dependent dielectric properties were carried out by means of AC conductivity (σac), imaginary dielectric constant (ε′′), loss tangent (tanδ), impedance and dielectric modulus (real and imaginary) measurements in frequency range of 50Hz–5MHz at room temperature. The structural properties investigated by using X-ray diffraction, scanning electron microscopy, and Fourier transform infrared spectroscopy. X-ray diffraction pattern and FTIR results revealed that synthesized samples are in single phase. It is observed that the dielectric constant (ε′′) and dielectric loss (tanδ) value decreases with increase in Ni2+ concentration (x). At low frequency the Maxwell type interfacial polarization was observed. Magnetization measurement shows that the Curie temperature of the samples increases with Ni2+ concentration, which is explained by a change in the A–O–B super exchange interaction.

ACCURATE DETERMINATION OF TORSION AND PURE BENDING MOMENT FOR VISCOELASTIC MEASUREMENTS

Measurements of time-dependent material properties in the context of linear viscoelasticity, at a given frequency and temperature, require accurate determination of both loading and deformation that are subjected to the testing materials. A pendulum-type viscoelastic spectroscopy is developed to experimentally measure loss tangent and the magnitude of dynamic modulus of solid materials. The mechanical system of the device is based on the behavior of the cantilever beam, and torsion and pure bending moment are generated from the interaction between a permanent magnet and the Helmholtz coils. The strength of the magnetic interactions may be determined with a material with known mechanical properties, such as aluminum 6061T4 alloy. The sensitivity of the torque measurement is on the order of one micro N-m level. With the high accurate torque measurement and deformation detection from a laser-based displacement measurement system, viscoelastic properties of materials can be experimentally measured in different frequency regimes. Sinusoidal driving signals are adopted for measuring complex modulus in the sub-resonant regime, and dc bias driving for creep tests in the low frequency limit. At structural resonant frequencies, the full-width-at-half-maximum (FWHM) method or Lorentzian curve fitting method is adopted to extract material properties. The completion of determining material properties in the wide frequency spectrum may help to identify the deformation mechanisms of the material and to create better models for simulation work.

The dominance of paramagnetic loss in microwave dielectric ceramics at cryogenic temperatures

Commercial manufacturers add transition metals and other impurities to high performance microwave ceramic compounds to improve their manufacturability. Measurements of microwave loss tangent were performed on Ba(Zn1/3Ta2/3)O3, ZrTiO4-ZnNb2O6, Ba(Zn1/3Nb2/3)O3, and BaTi4O9-BaZn2Ti4O11 ceramics. A marked increase in the loss at low temperatures is found in materials containing transition metal with unpaired d-electrons as a result of resonant spin excitations in isolated atoms (light doping) or exchange coupled clusters (moderate to high doping). The loss tangent can be drastically reduced by applying static magnetic fields. Our measurements also show that this mechanism significantly contributes to room temperature loss, but does not dominate.

Dynamic relaxation characteristics of thermally rearranged aromatic polyimides

The glass–rubber and sub-glass relaxation characteristics of ortho-functionalized aromatic polyimides and thermally rearranged polymers were investigated by dynamic mechanical and dielectric methods. Soluble polyimides (HAB–6FDA; APAF–ODPA) were synthesized by chemical and thermal imidization and subject to thermal rearrangement at elevated temperature. For the thermal exposure histories investigated, mass loss studies indicated partial conversion of the polyimide precursor, suggesting the formation of TR copolymers containing both benzoxazole units and residual imide segments. Measurement of storage modulus and loss tangent was used to follow the thermal rearrangement process in-situ as reflected in the suppression of the polyimide glass transition as a function of precursor structure, the nature of the ortho functional groups and prior thermal exposure. In addition, changes in the position and intensity of local relaxations detected across the sub-glass temperature range were correlated with the degree of thermal rearrangement in these polymers.

Magnetic and Dielectric Properties of &lt;I&gt;M&lt;/I&gt;-Type Sr-Hexaferrites with the Addition of Calcium Oxide and Silicon-Di-Oxide

M-type Sr-hexaferrites with compositions (SrO)1–x (La2O3) x 5.7Fe2O3, where x = 0.00 and SrO. 5.7Fe2O3 + [0.7 wt% CaO + 0.3 wt% SiO2] prepared by standard ceramic method using magnetite of Cox's bazar beach sand, Bangladesh have been investigated in the present work. Investigations have been performed by the measurements of permeability, loss tangent and dielectric constant of Sr-hexaferrites without and with the simultaneous addition of CaO and SiO2. Throughout the investigations, it has been observed that the magnetic and dielectric properties of Sr-hexaferrites improved significantly with the simultaneous addition of calcium oxide and silicon di-oxide.

The special features of the frequency dependence of phononless hopping conduction

Within the framework of perturbation theory the imaginary part of the phononless conduction of a lightly doped compensated semiconductor is calculated. It is shown that when the basis of localized atomic-like functions is used, the superlinear frequency dependence of the real part of the conduction corresponds to the approximately linear frequency dependence of the imaginary part of the conductivity. It has been found that at frequencies below the transition (crossover) frequency ωcr from the linear to quadratic frequency dependence of the real part of conductivity, the dielectric loss tangent depends weakly on the frequency and it is determined by the relationship of ħωcr to the width of the impurity band. It is shown that measurements of the dielectric loss tangent can provide information on the localization radius of impurity states.

High temperature dielectric constant and loss tangent measurements [advertisement

High temperature dielectric constant and loss tangent measurements [advertisement

Effect of Ca-substitution on the Magnetic and Dielectric Properties of Mn-Zn Ferrites

Spinel Mn-Zn ferrites with composition MnxZn0.4Ca0.6-2xFe2+xO4, where x = 0.10, 0.15, 0.20, 0.25 and 0.30 have been prepared by conventional ceramic technique sintered at 1300 °C for 4 hours. The influence of Ca-substitution on various properties of Mn-Zn ferrites have been studied in this work. Investigations were carried out by the measurements of Curie temperature, permeability, loss tangent, Q-factor, dielectric constant and AC resistivity of the samples. Curie temperature (Tc), the real part of initial permeability (µ´), loss tangent (tan ?), and AC resistivity have been found to be decreased while the Q-factor increases with the increase in Ca-content. The frequency characteristics of the dielectric constant and AC resistivity have been found to be decreased as the frequency increases. Maxwell-Wagner interfacial type of dielectric polarization was observed with the addition of Ca-content over the entire range of frequency considered. Keywords: Spinel ferrites; Sintering temperature; Initial permeability; Dielectric constant.© 2012 JSR Publications. ISSN: 2070-0237 (Print); 2070-0245 (Online). All rights reserved.doi: http://dx.doi.org/10.3329/jsr.v4i2.9752 J. Sci. Res. 4 (2), 297-306 (2012)

High temperature dielectric constant and loss tangent measurements [advertisement

High temperature dielectric constant and loss tangent measurements [advertisement

Loss tangent imaging: Theory and simulations of repulsive-mode tapping atomic force microscopy

An expression for loss tangent measurement of a surface in amplitude modulation atomic force microscopy is derived using only the cantilever phase and the normalized cantilever amplitude. This provides a direct measurement of substrate compositional information that only requires tuning of the cantilever resonance to provide quantitative information. Furthermore, the loss tangent expression incorporates both the lost and stored energy into one term that represents a fundamental interpretation of the phase signal in amplitude modulation imaging. Numerical solutions of a cantilever tip interacting with a simple Voigt modeled surface agree with the derived loss tangent to within a few percent.

High temperature dielectric constant and loss tangent measurements [advertisement

High temperature dielectric constant and loss tangent measurements [advertisement

Dielectric Anomaly in La0.7Sr0.3Fe0.05Mn0.95O3/BaTiO3 Composite

La0.7Sr0.3Fe0.05Mn0.95O3/BaTiO3 composite was synthesized and characterized by X-ray diffraction (XRD), transmission electron microscopic (TEM), ac conductivity (σac) and dielectric measurements (ϵr). The crystal structure of this composite have been determined by the Rietveld refinement powder XRD data at room temperature which confirmed by TEM. The dielectric constant (ϵr), dielectric loss (tan δ) and ac conductivity (σac) was investigated in the frequency (0.120–100 kHz) and temperature (293–401 K) The ac conductivity and loss tangent (tan δ) measurements conclude that the conduction mechanism in this sample is due to small polaron hopping. The composite sample exhibited broad dielectric anomalies in the vicinity of the ferroelectric-to-paraelectric transition temperature. The Curie-Weiss law was found to be valid at a temperature above the transition temperature.