Loss Tangent Peak Research Articles

Thermal, Tensile, Electrical, Dynamic Mechanical Thermal and Rheological Properties of Polyvinylidene Fluoride and Fluoroelastomer Composites Filled with Carbon Black

AbstractThe present work was focused on studying the effects of different CB loadings on the rheological, thermal, tensile, dynamic mechanical and electrical properties of polyvinylidenefluoride (PVDF) and FKM composites. To these ends, the CB grade and method chosen for compound preparation were CB (N330) and melt mixing, respectively. The composites were melt blended with CB at 190 °C in an internal mixer, after which the properties of filled and unfilled composites were compared. The presence of CB improved the mechanical properties, such as the Young's modulus and tensile strength, and increased thermal stability given the high thermal stability of CB and the interaction between the CB particles and the polymer matrices. The dynamic mechanical thermal analysis (DMTA) showed the glass transition temperatures of the composites. The analysis also revealed that the area under the loss tangent (tan δ) peak decreased and that the tan δ temperature of the rubber phase increased with CB loading. The increase in the electrical conductivity of the composites under different CB loadings was also examined, and the percolation threshold of conductive thermoplastic vulcanizate composite based on conductive CB was observed. The effect of CB and its content on rheological behavior of the PVDF/FKM blends was studied and the experimental data was correlated by a physical model named General Equation Model (GEM). A relation between rheology and conductivity of the blends with filler percolation was found.

Effect of quenching rate on electrical conductivity and glass formation of AgI–Ag2SO4–TeO2–B2O3 system

Effect of quenching rate on electrical properties and glass formation of 60AgI–40[0.6667Ag2SO4–0.3333(0.4TeO2–0.6B2O3)], 20AgI–80[0.6667Ag2SO4–0.3333(0.4TeO2–0.6B2O3)] systems was studied. Two systems of samples were prepared by melt quenching method with three different quench media such as air, ice and liquid nitrogen. X-ray diffraction and AC conductivity results show that cooling rate heavily effect the periodic order of atoms and electrical properties of samples respectively. Phase transition, glass transition and crystallization temperatures were determined from Differential scanning calorimetry results. The average AC conductivity of quenched samples increases with increasing the quenching rate. DC conductivity results show that the activation energy decreases with quenching rate. From the impedance spectroscopy, real and imaginary parts of impedances (Z′, Z″), conductivities were obtained and plotted Cole–Cole plots and these plots reveal grain and grain boundary resistance. The dielectric response of the system has been studied with frequency at different temperature, quenching media and activation energy calculated from loss tangent peak shift, which agrees with activation energy obtained from DC conductivity.

Optimised polyaniline–cadmium ferrite nanocomposite: synthesis, characterisation and alternating current response

In the present work, optimised polyaniline–cadmium ferrite (PANI–CdFe2O4) composite was prepared by chemical polymerization method. Comparative structural and morphological studies of PANI, CdFe2O4 and the composite were carried out by Fourier transform infrared spectroscopy, X-ray diffraction study and scanning electron microscopy. Highly crystalline nature of the composite composed of nanosized particles was confirmed by transmission electron microscopy studies. The dielectric loss tangent at room temperature for PANI, CdFe2O4 and the composite were investigated in the frequency range 50 Hz–5 MHz. The Maxwell–Wagner type polarisation in PANI and CdFe2O4 was confirmed by the decrease in their dielectric loss tangents with increasing frequency. But for the composite, a loss tangent peak due to relaxation losses implying resonance between hopping frequency of charge carriers and applied alternating current electric field was obtained. Debye type single relaxation in PANI and the distribution of relaxation in the composite were confirmed by their respective complex plane impedance plots and the plots simulated, equivalent RC network predicted and numerical values of R and C determined.

Effect of Plasticization on Ionic Conductivity Enhancement in Relation to Glass Transition Temperature of Crosslinked Polymer Electrolyte Membranes

The relationship between glass transition (Tg) and ionic conductivity (σ) of an amorphous crosslinked polymer electrolyte membrane (PEM) was examined based on ion–dipole complexation between dissociated lithium cations and ether oxygen of poly(ethylene glycol diacrylate) and plasticization by succinonitrile (SCN). In a binary PEM consisting of a lithium salt/polymer network, Tg increased due to a strong ion–dipole interaction, whereas σ declined due to lower ion mobility coupled to reduced chain mobility. Above the threshold salt concentration of 7 mol %, dual loss tangent peaks were observed in dynamic mechanical studies, which may be ascribed to segmental relaxations of ion–dipole complexed networks and that of polymer chains surrounding the undissociated lithium salt acting like “fillers”. Upon SCN plasticization, these two peaks merged into one that was further suppressed below Tg of the pure network, whereas σ improved to the superionic conductor level. The role of plasticization on the ionic conduct...

Rheology characterization, dynamic mechanical, thermal, and mechanical properties of LGF/TPU/PBT/PTW composites

Long glass fibers reinforced thermoplastic polyurethane and poly(butylene terephthalate) with the compatibilizer of poly(ethylene‐butylacrylate‐glycidyl methacrylate copolymer) (LGF/TPU/PBT/PTW) composites were prepared by using self‐designed impregnation device. Various rheological plots including viscosity curve, storage modulus, loss modulus, loss angle, Cole‐Cole plot, and relaxation spectrum were used to characterization of rheological properties. Dynamic mechanical thermal analysis (DMA) results indicated that “double tan δ behavior” of composites is observed. The activation energies of α and β‐relaxation process of loss modulus and tan δ of the LGF/TPU/PBT/PTW composites gradually increased with long glass fibers content. Moreover, activation energies for the glass transition relaxation determined from loss tangent peaks are more reliable than using loss modulus criterion. Thermal properties of composites are studied by differential scanning calorimetry (DSC) and thermogravimetric analyses (TGA). Mechanical properties of composites are studied. POLYM. COMPOS., 39:794–806, 2018. © 2016 Society of Plastics Engineers

Tuning of Dielectric Parameters of (NiFe2O4) x /CuTl-1223 Nano-superconductor Composites by Temperature and Frequency

Nickel ferrite (NiFe2O4) nanoparticles and Cu0.5Tl0.5Ba2Ca2Cu3O10−δ (CuTl-1223) superconductor were prepared separately and then mixed in an appropriate ratios at the final stage to obtain (NiFe2O4) x /CuTl-1223 (x = 0, 0.5, and 1.0 wt%) nano-superconductor composites. There was no significant change observed in crystal structure of the host CuTl-1223 superconducting matrix after the addition of NiFe2O4 nanoparticles. The value of zero-resistivity critical temperature { T c(R = 0) (K)} was decreased with increasing content of these nanoparticles in these composites. Maximum values of dielectric loss tangent (tanδ) at lowest possible frequency of 40 Hz were increased with the increase of operating temperature, while its values were decreased and become almost zero at higher frequencies for all these samples at all operating temperatures. A peak in dielectric loss tangent was shifted towards lower frequency values with the addition of these nanoparticles in CuTl-1223 superconducting matrix. The dielectric loss tangent peak was also shifted towards lower frequency values in all these samples with increasing operating temperature, which shows the relaxator-like behavior in these samples. The dielectric parameters of these composites can be tuned by frequency, operating temperatures, and nature and content of these nanoparticles.

Plasticizer loading in acoustic encapsulants

Acoustically transparent elastomers are the windows through which the United States Navy views the ocean. For acoustic clarity and sensitivity, it is important that the elastomer operates well outside damping conditions as dictated by the temperatures and frequencies of interest. Damping behavior is characterized by a peak in the loss tangent. However, the temperature and frequency location of this peak can shift in response to absorbed plasticizing fluids. This material characteristic is under investigation using dynamic mechanical analysis (DMA) to assess its dependence on the plasticizer and polyurethane component chemistry. In this first stage of the research, a temperature range from −100 to 100 °C and samples saturated with fluid were explored by DMA to determine the limiting behavior of the samples, enabling more detailed investigation in future work. Association of absorbed plasticizers with polyurethane components by polarity was demonstrated in the results by the shifting of the appropriate hard and soft block loss tangent peak.

Effects of ultrasound on glass transition temperature of freeze-dried pear (Pyrus pyrifolia) using DMA thermal analysis

The effect of ultrasound pretreatment at various power (360W, 600W and 960W, frequency 20kHz) on the glass transition temperature of freeze dried pear (Pyrus pyrifolia) has been studied. DMA temperature plots were divided into four sections (A – glassy region, B – transition region, C – Rubbery plateau region and D – terminal region) with the aim to analyze their properties changed with sonication. Under the same freeze drying condition, with the increase in ultrasonic power, dried pear showed higher glass transition in terms of storage modulus, loss modulus and loss tangent peak. Also a decrease in aw (0.31–0.23) and in moisture content (0.12–0.08g/gd.b.) has been observed. Samples pretreated with ultrasound showed a better texture profile and much porous structure compared to control one. The results from the study indicated that, ultrasound pretreatment prior to freeze drying can improve the stability during storage of freeze dried pear.

Probing of Polymer Surfaces in the Viscoelastic Regime

In this Feature Article, we discussed the experimental and modeling methods and analyzed the limitations of the surface probing of nanomechanical properties of polymeric and biological materials in static and dynamic regimes with atomic force microscopy (AFM), which are widely utilized currently. To facilitate such measurements with minimized ambiguities, in this study we present a combined method to evaluate the viscoelastic properties of compliant polymeric materials. We collected force-distance data in the static regime for a benchmark polymer material (poly(n-butyl methacrylate)) with an easily accessible glass-transition temperature (about 25 °C) at different loading rates and different temperatures across the glassy state, glass-transition region, and rubbery state. For this analysis, we exploited a Johnson-modified Sneddon's approach in a combination with the standard linear solid model. Critical experimental steps suggested for robust probing are (i) the use of a tip with a well-characterized parabolic shape, (ii) probing in a liquid environment in order to reduce jump-in phenomenon, and (iii) minute indentations to ensure the absence of plastic deformation. Whereas the standard Sneddon's model generates quantitatively adequate elastic modulus values below and above the glass transition, this traditional approach can significantly underestimate actual modulus values in the vicinity of the glass-transition region (15 °C above or below Tg), with major deviations occurring at the loss tangent peak. The analysis of the experimental data with Sneddon's model for the elastic region (glassy and rubbery states) and Johnson's model for the viscoelastic region allowed for the restoration of the universal master curve and the evaluation of the storage modulus, loss modulus, loss tangent, relaxation times, and activation energies of the polymer surface across the glass-transition region and at relevant loading rates.

Enhanced mechanical properties of graphene/natural rubber nanocomposites at low content

Graphene/natural rubber (GE/NR) nanocomposites were prepared by a modified latex mixing method combined with in situ chemical reduction. It was found that the GE nanosheets are well dispersed and have strong interfacial interaction with NR. Thus, adding a low content of GE can remarkably increase the tensile strength and the initial tensile modulus of NR. With incorporation of as low as 0.5 phr of GE, a 48% increase in the tensile strength and an 80% increase in the initial tensile modulus are achieved without sacrificing the ultimate strain. But further increasing the GE loading degrades the tensile strength and the ultimate strain. Dynamic mechanical measurement indicates that the storage modulus of the nanocomposites is greatly enhanced with addition of GE, while the loss tangent peak is depressed due to the reduced mobility of the rubber molecules. The reinforcement effect of GE on NR is interpreted as a change in the strain induced crystallization and network structure of the nanocomposites, based on the analysis of Mooney − Rivlin plots and the tube model.© 2013 Society of Chemical Industry

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.

Lecithin-based emulsions for potential use as saliva substitutes in patients with xerostomia – viscoelastic properties

The purpose of the present study was to investigate lecithin-rice bran oil rheological properties with the view to consider these as potential saliva substitutes in patients with severe xerostomia and salivary hypofunction. Pseudo-ternary phase diagrams of rice bran oil, lecithin and water mixtures were constructed and characterised using polarising light microscopy. Viscoelastic properties, which we hypothesise are important determinants in product performance, were analysed using both flow and oscillatory rheology. Rheological properties were influenced by composition, frequency and shear stress. Frequency-dependent viscoelasticity was observed in some formulations where viscosity dominated (tanδ>1) at frequencies under 5 Hz and elasticity dominated (tanδ<1) at higher frequencies. Threshold frequencies were determined for each formulation, where a peak in loss tangent was observed, coinciding with a reduction in the storage modulus and increase in loss modulus. The frequency-dependent behaviour of emulsions are of interest because these combinations exhibit viscous behaviour at low frequencies, which may improve lubrication of the oral cavity at rest, whereas increased elasticity at higher frequencies may improve retention during higher-shear tasks such as swallowing and speaking.

Reinforcement effect of cellulose nanowhisker on bio-based polyurethane

Abstract Bio-based polyurethane (BPU)/cellulose nanowhisker composites synthesized using castor oil-based polyol were prepared by adding cellulose nanowhiskers during preparation of the prepolymer. Chemical modification of cellulose nanowhiskers was performed to enhance dispersion of the cellulose nanowhiskers, and modified cellulose nanowhiskers (m-CNWs) were covalently bonded with the BPU matrix to improve interfacial adhesion. The tensile strength and modulus of the m-CNW reinforced BPU composites were significantly improved, as compared with the neat BPU. The elongation at break of the BPU/m-CNW composites decreased with increasing m-CNW content, indicating that m-CNW made the BPU stiff and rigid. Dynamic mechanical analysis showed that the storage modulus was increased and the loss tangent peak was shifted toward higher temperatures by incorporation of m-CNW. This was due to the increased cross-linking density of the rubber network resulting from the strong interaction between m-CNW and the BPU matrix. Furthermore, the m-CNW enhanced the thermal stability of the BPU composites. This research demonstrated the potential for utilization of cellulose nanowhiskers as eco-friendly reinforcement in biopolyurethane composites.

Influence of process parameters on microstructure and mechanical properties of starch-cellulose acetate/silver sulfadiazine matrices prepared by melt extrusion

Starch-cellulose acetate matrices containing silver sulfadiazine were produced using melt extrusion for application in drug delivery devices (DDDs). The influence of the extrusion parameters (screw speed and temperature) on the morphological and mechanical properties of the matrices was evaluated at three different levels. The microstructural characterization of all matrices showed that an increase in the screw speed enhances the porosity and drug dispersion, while an increase in the extrusion temperature decreases the pore diameter of the matrices. Mechanical results did not show significant differences between the elastic modulus values for the matrices; however, a faster screw speed led to higher ultimate strength and strain at failure values. Results obtained in the dynamic mechanical analysis showed that the glass transition and loss tangent (tan δ) peak values became higher with increasing screw speed and temperature.

Electrical behaviors of (1-x)BZT07-xBNWT lead free solid solution binary system

Solid solutions of the (1−x)Ba(Zr0.07Ti0.93)O3-xBa((Ni0.5W0.5)0.1Ti0.9)O3 system with 0.05 ≤ x ≤ 0.2, were fabricated via a solid-state reaction technique. All samples exhibited a pure phase perovskite structure. The x = 0.05 samples exhibited very high dielectric constants (>60,000) for temperatures over 400°C, while the x = 2.0 samples had a higher degree of dielectric constant stability over a wide temperature range. The ceramics also showed a dielectric relaxor behavior. The frequency dependence of the loss tangent peak was observed to follow an Arrhenius law where the activation energies increased with increasing Ba((Ni0.5W0.5)0.1Ti0.9)O3 content. The result suggests that the addition of Ba((Ni0.5W0.5)0.1Ti0.9)O3 has strong effects on the properties this ceramic system.

Viscoelastic melt rheology and time–temperature superposition of polycarbonate–multi-walled carbon nanotube nanocomposites

Abstract This work investigates the linear and non-linear viscoelastic melt rheology of four grades of polycarbonate melt compounded with 3 wt% Nanocyl NC7000 multi-walled carbon nanotubes and of the matching matrix polymers. Amplitude sweeps reveal an earlier onset of non-linearity and a strain overshoot in the nanocomposites. Mastercurves are constructed from isothermal frequency sweeps using vertical and horizontal shifting. Although all nanocomposites exhibit a second plateau at ∼105 Pa, the relaxation times estimated from the peak in loss tangent are not statistically different from those of pure melts estimated from cross-over frequencies: all relaxation timescales scale with molar mass in the same way, evidence that the relaxation of the polymer network is the dominant mechanism in both filled and unfilled materials. Non-linear rheology is also measured in large amplitude oscillatory shear. A comparison of the responses from frequency and amplitude sweep experiments reveals the importance of strain and temperature history on the response of such nanocomposites.

Dielectric properties, impedance analysis and modulus behavior of CaTiO3 ceramic prepared by solid state reaction

Calcium titanate (CaTiO3) with the general formula for perovskites, ABO3, is of technological importance, particularly with regard to dielectric properties. In this work, CaTiO3 ceramic material was prepared by the conventional solid state reaction method. The dielectric properties, impedance characteristics and modulus behavior of the CaTiO3 ceramic material sintered at 1240°C were investigated in the frequency range of 10−2–106Hz and temperature range of 100–250°C. The XRD analysis of the sintered CaTiO3 shows that it is an orthorhombic structure with lattice parameters a=5.4398Å, b=7.6417Å, and c=5.3830Å. The FESEM micrograph shows a significant difference in grain size distribution ranging from 0.26 to 2.32μm. The AC conductivity, σAC, is found to increase with increasing temperature within the frequency range of 10−2–106Hz confirming the hopping of electrons to be the conduction mechanism. Due to the decreasing values of the frequency exponent s with increasing temperature, the results of the σAC are discussed using the correlated barrier height (CBH) model. For dielectric studies, the dielectric constant, ε′ is found to decrease with increasing frequency. In the whole temperature range of 100–250°C, high and low frequency plateau are observed. Each converges at high frequency (>105Hz) for all the temperatures. The frequency dependence of loss tangent, tanδ, decreases with rise in temperature, with the loss tangent peak shifting to higher frequency. Due to its dielectric characteristics, it is a suitable candidate for developing a variety of capacitors. For the master modulus plot, the shapes remain unchanged in the temperature range considered. The Cole–Cole plots reveal that two primary relaxation processes exist in the sample for each temperature. The Nyquist plots reveal that at temperatures below 150°C, a linear response in the imaginary part of the impedance, Z′′, is noticed. At and above 175°C, the linear response gradually changes to a semicircle arc. The modulus behavior indicates the presence of correlation between the motions of mobile charge carriers. The plots of Arrhenius diagram of relaxation times of loss tangent, τtanδ, and imaginary part of dielectric modulus, τM′′, obey the Arrhenius law, where the activation energies calculated from the slopes are 2.09 and 2.38eV respectively.

Investigation of dielectric relaxation behavior of electrospun titanium dioxide nanofibers using temperature dependent impedance spectroscopy

The electrospinning method has been utilized in the fabrication of titanium dioxide nanofibers (TNFs) with an average diameter of ∼50nm and length of ∼100μm. Effect of temperature on the dielectric relaxation behavior of the fabricated nanofibers have been studied using AC impedance spectroscopy. The morphological, structural and compositional aspects as well as the optical properties of the TNFs have been investigated by field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), energy-dispersive x-ray spectroscopy (EDX) and ultraviolet–visible (UV–vis) absorption spectrum. The permittivity behavior of the device at the frequency below 102Hz shows the relaxation contribution along with the electrode polarization. Dielectric loss peak in loss tangent also confirms the presence of relaxing dipoles in TNFs. The AC conductance as a function of frequency confirms the semiconducting nature of TNFs and obeys Jonscher's power law except a small deviation in the low frequency region. DC conductivity increases with increase in temperature.

Dynamic mechanical properties of polystyrene‐co‐styrenesulfonic acid copolymers neutralized with aliphatic diamines

AbstractIn this article, we reported the effects of the addition of various aliphatic diamines (ADAs) on the dynamic mechanical properties of poly(styrene‐co‐styrenesulfonic acid) copolymers. It was found that the ionic modulus decreased with increasing chain length of ADAs but increased for the ADA12‐containing ionomers. Upon the neutralization of the copolymers with ADAs, a minor change in the size and position of the matrix loss tangent peak was observed. However, the position of the cluster loss tangent peaks shifted to lower temperatures, and the shift rate depended on the chain length of ADAs. Thus, it was suggested that the ADAs acted mainly as preferential plasticizer for the cluster regions. In addition, the effect of the amount of ADA on the difference between the matrix and cluster temperatures of the ionomers was strongest than that of the type of ADA or ion content. The X‐ray peak of ADA12 suggested that the ADA12 acted both as plasticizer and as filler. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013

Dielectric properties and morphology of polymer electrolyte based on poly(ɛ-caprolactone) and ammonium thiocyanate

In this paper, the frequency dependence of dielectric and electric modulus as well as morphological characteristics of poly (ɛ-caprolactone) (PCL)-ammonium thiocyanate (NH4SCN) polymer electrolyte are investigated. Dielectric analysis shows that electrode polarization masks the dielectric relaxation. The loss tangent peak shifts towards higher frequency with increasing salt content up to 26 wt-%. Long range conductivity relaxation is indicated as a resonance peak in imaginary electric modulus, M″ versus frequency plot. The normalised peaks of M″ and Z″ (imaginary impedance) with log f is observed to overlap. This implies that the relatively fast segmental motion of the polymer couples with ion diffusion. Hence, transport is enhanced at room temperature, which is much higher than the glass transition temperature of PCL (−60 °C). From morphology studies, the number of spherulites are observed to increase with a reduction in their size when more salt is added to PCL. This observation is accompanied by an enhancement in conductivity and increase in the amorphous phase. When 32 wt-% of salt is added, agglomeration appears due to the formation of ion clusters or higher aggregates as deduced from SEM micrographs.