Dynamic Dielectric Analysis Research Articles

Multifunctional Performance of Hybrid SrFe12O19/BaTiO3/Epoxy Resin Nanocomposites.

Polymer matrix nanocomposites are widely studied because of the versatility of their physical and mechanical properties. When these properties are present simultaneously, responding at relative stimuli, multifunctional performance is achieved. In this study, hybrid nanocomposites of SrFe12O19 and BaTiO3 ceramic particles dispersed in an epoxy resin matrix were fabricated and characterized. The content of SrFe12O19 was varying, while the amount of BaTiO3 was kept constant. The successful fabrication of the nanocomposites and the fine dispersion of the ceramic particles was verified via the morphological and structural characterization carried out with X-ray Diffraction patterns and Scanning Electron Microscopy images. Dielectric response and related relaxation phenomena were studied by means of Broadband Dielectric Spectroscopy. Dielectric permittivity augments with filler content, while the recorded relaxations, with descending relaxation time, are: (i) interfacial polarization, (ii) glass-to-rubber transition, (iii) intermediate dipolar effect, and (iv) re-orientation of polar-side groups of the main polymer chain. SrFe12O19 nanoparticles induce magnetic properties to the nanocomposites, which alter with the magnetic filler content. Static and dynamic mechanical response improves with filler content. Thermogravimetric analysis shown that ceramic particles are beneficial to the nanocomposites' thermal stability. Glass transition temperature, determined via Differential Scanning Calorimetry, was found to slightly vary with filler content, in accordance with the results from dynamic mechanical and dielectric analysis, indicating the effect of interactions occurring between the constituents. Examined systems are suitable for energy storing/retrieving.

High Strain Rate Failure Behavior of Polycarbonate Plates due to Hypervelocity Impact

Developing a fundamental understanding of how polymers respond during hypervelocity impact (HVI), a high strain rate process, is crucial for the potential use of polymers in HVI protection systems. Here, we present the high-strain-rate impact behavior of commercially available polycarbonates with two different molecular weights, 42 and 21 kg/mol. A powder gun and a two-stage light-gas gun were used to achieve the velocities (v0) of a 4 mm projectile impacting the polycarbonate targets over the range of 400–6,500 m/s. The deformation behavior of the polymer during the impact event was captured using high-speed cameras. The impact caused a variety of responses, ranging from deflection of the projectile to complete perforation for higher v0, leading to major debris cloud formation. These debris clouds consist of both fluid- and dust-like ejecta. The fluid-like debris cloud indicates the melting of polymer caused by the conversion of kinetic energy to thermal energy and subsequent adiabatic heating. The dust-like response can likely be attributed to the brittle failure behavior of polymers, as the polymer became brittle at a high strain rate. Dynamic mechanical analysis (DMA) and dielectric thermal analysis (DETA) on the polycarbonate samples used here indicate an approximately 40 °C increase of Tg with increasing frequency from 1 Hz to 106 Hz, and such an increase has likely led to brittle behavior. While the leading-edge velocity of the debris clouds and perforation diameters scale linearly with v0, we found negligible differences in the HVI response for the two molecular weights of polycarbonate tested here. This study displays the importance of v0 and thickness contributing to responses of polycarbonates undergoing HVI.

Membranes for Cation Transport Based on Dendronized Poly(epichlorohydrin-co-ethylene oxide). Part 1: The Effect of Dendron Amount and Column Orientation on Copolymer Mobility.

Dendronized polyethers give rise to columnar LC structures which can successfully act as cation transport materials. Therefore, we prepared two different materials, based on Poly(epichlorohydrin-co-ethylene oxide) (PECH-co-EO) grafted with methyl 3,4,5-tris[4-(n-dodecan-1-yloxy)benzyloxy] benzoate, containing 20% or 40% modified units, respectively. The obtained polymers were characterized by differential scanning calorimetry (DSC), X-ray diffraction and optical microscopy between crossed polars (POM) and compared to the unmodified PECH-co-EO. In order to reach efficient transport properties, homeotropically oriented membranes were prepared by a fine-tuned thermal annealing treatment and were subsequently investigated by dynamic mechanical thermal analysis (DMTA) and dielectric thermal analysis (DETA). We found that the presence of the dendrons induces a main chain partial crystallization of the polyether chain and coherently increases the polymer Tg. This effect is more evident in the oriented membranes. As for copolymer orientation upon annealing, the cooling rate and the annealing temperature were the most crucial factors. DMTA and DETA confirmed that grafting with the dendron strongly hinders copolymer motions, but did not show great differences between unoriented and oriented membranes, regardless of the amount of dendrons.

Evolving Fault and Parallel Switching for SF6 Circuit Breakers

A special stress for circuit breaker is the occurrence of evolving fault or parallel switching condition. These switching cases are not standardized by international standards, but may occur in service and may create problems for the breaker. In the past, it was a problem mainly with oil circuit breakers and some types of air-blast circuit breakers but lesser known with SF6 circuit breakers. In the meantime, with upcoming new switching technologies along with changed operating duties, some doubts exist that these switching cases may become an issue again. This paper explains in detail the background of these stresses and presents a method to evaluate the capability of SF6 circuit breakers for such situations. The theoretical evaluation involves network calculations, gas flow simulations, and dynamic dielectric analysis. It is important to note here that several tests have been done in the past for evolving and parallel switching faults for both puffer as well as self-blast circuit breakers with the knowledge available at that time. These test results are used to validate the outcome of the theoretical evaluation which will help in better prediction of the circuit breaker behavior before performing actual tests. It can be concluded that theoretical simulation may, in majority of the cases, serve as sufficient proof to show feasibility for such cases.

Thermal, mechanical and dielectric behaviour of poly(aryl ether ketone) with low melting temperature

New poly(aryl ether ketone)s (PAEKs) with a low melting temperature (relative to PEEK) are of interest in order to simplify the manufacturing of high-performance polymers or composites. In this study, we propose to investigate the physical properties of a new PAEK from Victrex, namely PAEK LM. Combinations of thermal analyses were used as follows: standard and modulated temperature differential scanning calorimetry, dynamic mechanical analysis, dynamic dielectric analysis and guarded hot plate technique. We found that the global mechanical, dielectric and thermal properties are very similar to the PEEK reference. The glass transition temperature was observed in the same range than PEEK (∼ 150 °C) while the melting temperature Tm was measured at 307 °C for PAEK LM which is about 35 °C below the melting temperature of PEEK. The degree of crystallinity of PAEK LM was found to be 27% while for PEEK it is 38%, depending on the processing conditions. This work explored crystalline structure–property relationships to explain the behaviour of PAEK LM.

Thermophysical characterization of a reversible dynamic polymer network based on kinetics and equilibrium of an amorphous furan-maleimide Diels-Alder cycloaddition

The equilibrium and kinetics of the furan-maleimide Diels-Alder (DA) reaction for the formation of a reversible network were studied by calorimetry between 25 °C and 90 °C using an amorphous bismaleimide eliminating solvent use. The relationship between the equilibrium conversion xeq with temperature and the effect of dilution were simulated. The glass transition-conversion relationship of the reversible network was established.The thermophysical properties of the reversible network were linked to the kinetics and equilibrium of the DA system, and studied by dynamic mechanical analysis (DMA), dielectric analysis (DEA) and rheometry. Below Tg the reversible network behaves like an irreversible network; however, above Tg, a decrease in the rubber tensile storage modulus was observed due to a reduction of cross-link density caused by the retro DA reaction. DEA revealed that above Tg, an interface is formed between released bismaleimide molecules and the remaining network. The rheological behavior is related to xeq and the lifetime of the reversible covalent bonds. When xeq is higher than the gelation conversion xgel (below 90 °C), the system gels at constant xgel. An elastic strengthening effect is observed in a transition region between 90 °C and 115 °C. Above 115 °C the system is reaching a viscous melt behavior. These observations are important for the application of this network as a self-healing material and as a recyclable elastomer or thermoset.

Dynamic molecular mobility of polyurethane by a broad range dielectric and mechanical analysis

The dynamic molecular mobility of poly(2-hydroxypropyl methacrylate) (PHPMA) base polyurethane (PU) was studied over a broad range of frequency and temperature by combining dynamic dielectric spectroscopy and dynamic mechanical analysis. Two hydrated levels were considered in this study: dry and room humidity states. In dry state, two secondary relaxations γ and β are identified. And in room humidity state, a βsw mode is pointed out. These modes are well known in poly(hydroxylalkyl methacrylate)s. The main α relaxation is influenced by humidity and crosslinks. The Kramers-Kronig transform is used to reveal an ionic conductivity σionic. Relaxation times extracted from dielectric and mechanical analyses are coherent for PU and PHPMA. This correlation allows us to propose an interpretation of relaxations at a molecular level.

Electrical, thermal and mechanical properties of poly-etherimide epoxy-diamine blend

This work deals with the study of thermoset-thermoplastic blend forming an epoxy-amine/poly-etherimide phase separated to assess the dielectric and thermal performances. These materials would be good candidates to replace the passivation layer in semiconductors, particularly ones used as switches in power electronic applications. Polyimide and Parylene are usually quoted and studied. Mixtures based on polymers would be a novel candidate that can manage to be an insulator for the system. The modified and non-modified systems where characterized by transmission electron microscopy, scanning electron microscopy, differential scanning calorimetry, thermogravimetric analysis, dynamic mechanical analysis, dielectric analysis and analytical simulation was carried out on dielectric measurements. These complementary techniques were used first to investigate the presence of the phase separation phenomenon and second to quantify the separated nodules size. The effect of this phase separation was examined and showed enhancement in the dielectric values compared to the pure epoxy system. It was finally simulated to show a close assumption of what is found experimentally.

Dielectric relaxation phenomena in flax fibers composite

In this work, a study of the dynamic dielectric analysis of the unidirectional epoxy composite: flax-fibre-reinforced epoxy (FFRE) was investigated. In this composite, three relaxation processes were identified. The first one is the water dipoles polarization imputed to the presence of polar water molecules in flax fiber. The second relaxation process associated with conductivity occurs as a result of the carriers charges diffusion. As for the third dielectric relaxation associated with the interfacial polarization effect is attributable to the accumulation of charges at the fibers/matrix interface. The analysis of the Maxwell-Wagner-Sillars (MWS) and the water dipoles polarizations using the Havriliak-Negami model revealed the high adhesion of flax fibers in the matrix. This analysis was supported by the thermal properties using a Differential Scanning Calorimety (DSC).

Phase Transitions and Relaxation Behaviors in Barium Strontium Titanate Ceramics Determined by Dynamic Mechanical and Dielectric Analysis

Barium strontium titanate (Ba1-xSrxTiO3) ceramics were prepared by solid-state reaction method. XRD patterns showed that BT (x = 0) and BST2 (x = 0.2) ceramics presented tetragonal phase, while BST4 (0.4) and BST6 (0.6) ceramics showed cubic phase at room temperature. The relative permittivity and dissipation factor of Ba1-xSrxTiO3 ceramics with temperature of 125–425 K were characterized at 1–100 kHz by LCR meter. The Young's modulus and internal friction of Ba1-xSrxTiO3 ceramics in the range of 125 K–425 K at different vibration frequencies were tested by a Dynamic Mechanical Analysis (DMA) system. Compared with the dielectric measurement, mechanical analysis was more sensitive to reflect the phase transition and relaxation process. All Ba1-xSrxTiO3 samples showed three phase transitions, the transition temperatures decreased and the phase transition diffused as Sr content increased. Besides, a relaxation process caused by the interaction between domain walls and lattice defects emerged in pure BT ceramic, while it disappeared in all BST ceramics.

Low-Temperature Carrot Cooking Supported by Pulsed Electric Field—DMA and DETA Thermal Analysis

The paper deals with carrot processing that com- bines the effect of the electric pulse loading with the low- temperature heating. The pulse procedure was formed by one 10-ms long electric pulse (amplitude, 600 V/cm; basic frequency, 20 kHz) on the 160-ms long electric background less than 30 V/cm. The procedure was followed by the com- bined dynamic mechanical analysis (DMA) and dielectric thermal analysis (DETA) tests with the initial temperature of 30 °C and final temperature of 90 °C. Humidity in the test chamber was kept at 90 % during the whole heating test, with the heating rate of 1 °C/min. During the whole test, both components of the complex modulus of elasticity (DMA) of the specimen as well as both components of the specimen's permittivity (DETA) were registered. A similar test was also performed with other specimens with- out the initial pulse procedure. Ratios of corresponding data (storage modulus, loss modulus, dielectric constant, and dielectric loss) are approximately constant up to the temperature of approximately 70 °C where it starts to reduce substantially. The obtained results denote that can be processed using electric pulses reaching the similar state as during the tissue heating.

Relaxation behavior in clay-reinforced polymer nanocomposites

The effect of clay reinforcement on dielectric, conductivity, and mechanical relaxation behavior of a polymer clay nanocomposite film is reported. Polymer nanocomposite is composed of three component polymers (polyacrylonitrile) as a host matrix, salt (LiPF6) as conducting species, and clay (sodium montmorillonite) as intercalant. The macroscopic parameters like polymer glass transition temperature and available free mobile charge carriers have been analyzed properly using dynamic mechanical analysis and dielectric analysis. Dielectric analysis indicated distribution of relaxation time as a function of clay concentration, whereas conductivity spectrum exhibited dispersion at lower frequency followed by saturation region at intermediate frequency. The dispersion behavior is related to the electrode polarization attributed to faster ion dynamics. The dielectric and conductivity relaxation are in excellent correlation with mechanical relaxation owing to the changes in glass transition temperature due to polymer-ion-clay interaction. The proposed mechanism is a sequel to the experimental results.

Elastic softening near the phase transitions in (1 − x)Bi1/2Na1/2TiO3-xBaTiO3 solid solutions

Phase transitions in sol–gel-derived (1 − x)(Bi1/2Na1/2TiO3)-xBaTiO3 (0 ≦̸ x ≦̸ 0.06) solid solutions were investigated via dynamic mechanical, dielectric, and ferroelectric analyses. Structural phase transition was observed from both noncentrosymmetric ferroelectric to nonpolar (antiferroelectric) forms (FE-AFE) at temperatures ranging from ∼120 °C to ∼210 °C, and from antiferroelectric to paraelectric forms (AFE-PE) at temperatures ranging from ∼250 °C to ∼320 °C for 0 ≦̸ x ≦̸ 0.06. The former transition is accompanied by a significant and broad elastic softening or soft-mode process, and the latter is of typical diffused type. The dynamic mechanical scaling exponent and critical scaling exponent are used to characterize these two phase transitions, respectively. The temperature-dependent polarization showed an abnormal trend unlike other reported ferroelectrics, confirming the presence of two different phases: FE and AFE. The d33 piezoelectric constant increases with increasing x up to the morphotropic phase boundary. It is suggested that the dynamic mechanical scaling exponents could be used to characterize the mobility of the polar domains and the elastic softening processes, which are closely related to abnormal pyroelectric properties and piezoelastic hardening behaviors.

Influence of two carbon plies on adhesion of unidirectional flax‐fibers reinforced epoxy composites

In this work, we undertook a comparative study of the dynamic dielectric analysis of two unidirectional epoxy composites: flax‐fiber‐reinforced epoxy and flax/carbon‐fiber‐reinforced epoxy (FCFRE). In both composites, three relaxation processes were identified. The first one is the water dipoles polarization imputed to the presence of polar water molecules in flax fiber. The second relaxation process associated with conductivity occurs as a result of the carriers charges diffusion noted for high temperature above glass transition and low frequencies. As for the third dielectric relaxation associated with the interfacial polarization effect is attributable to the accumulation of charges at the fibers/matrix interface. The presence of two carbon plies in the reinforcement gives rise to two interfacial polarization effects in the FCFRE composite. The analysis of the Maxwell–Wagner–Sillars and the water dipoles polarizations using the Havriliak–Negami model revealed that the presence of two plies of carbon can locally decrease the adhesion of flax fibers in the matrix. This analysis was supported by the thermal properties using a differential scanning calorimety and the mechanical properties using a short beam shear test. POLYM. COMPOS., 241–253, 2016. © 2014 Society of Plastics Engineers

Silylated montmorillonite as nanofillers for plasticized PVC nanocomposites: Effect of the plasticizer

Poly(vinyl chloride) (PVC) nanocomposites were prepared by compounding PVC with different clay minerals, which were previously dispersed into dioctyl phthalate (DOP) or epoxidized soybean oil (ESO) as plasticizers, with the help of an ultrasonication. Sodium montmorillonite (Na+-Mt) and those obtained from its functionalization with N-(2-aminoethyl-)-3-aminopropyl-trimethoxy-silane (NH2-Mt) or 3-mercaptopropyl-trimethoxy-silane (SH-Mt), as well as a commercial organoclay, Cloisite 30B, were employed as the nanoparticles. The incorporation of amino or mercaptosilane on the Na+-Mt surface was estimated by Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD) and thermogravimetric analysis (TGA). The clay PVC nanocomposites containing 2.5phr of different clay minerals were characterized by XRD, dynamic mechanical analysis, thermal degradation and dielectric analysis. It was found a high exfoliation degree for the nanocomposites containing silylated clays, as suggested by the absence of reflections. Na+-Mt also displayed a high exfoliated structure for system plasticized with ESO. The presence of different clay minerals resulted in an increase of the storage modulus without affecting the glass transition temperature. Regarding thermal stability, those systems plasticized with ESO presented the best results obtained from thermogravimetric analysis, and the presence of Cloisite 30B, a clay mineral modified with ammonium salt, presented the worst performance in both plasticized systems.

Dynamic Mechanical and Dielectric Properties of Poly(vinylidene fluoride) and Epoxidized Natural Rubber Blends

The blending of semi-crystalline polymer, poly (vinylidene fluoride), (PVDF) and uncross-linked elastomer epoxidized natural rubber with 50 mol% epoxide (ENR-50) blends were prepared in an internal mixer by melt mixing process. Dynamic mechanical analysis (DMA) and dielectric analysis (DEA) of PVDF/ENR-50 blends were investigated. It was found that the pure PVDF showed higher storage modulus than that of the pure ENR-50 and storage modulus of the PVDF/ENR blends decrease with increasing ENR-50 content. Furthermore, PVDF showed two relaxation peaks correspond to αa-relaxation and αc-relaxation, while ENR-50 showed only a single relaxation that is related to α-relaxation or glass transition temperature (Tg). Two relaxation peaks were observed in the PVDF/ENR-50 blends due to phase separation. However, the maximum peak of relaxation shifted toward to higher and lower temperature compared with the pure components which indicates the partial miscible blends. Moreover, at high temperature, the neat polymer and blends showed a sharp increase of loss factor (ε) that correspond to conductivity and/or Maxwell-Wagner-Sillar (MWS) process.

A new series of fluorinated alicyclic-functionalized polyimides derivated from natural-(D)-camphor: Synthesis, structure–properties relationships and dynamic dielectric analyses

A series of novel fluorinated alicyclic-functionalized polyimides (FPI-x) were prepared from a new alicyclic-functionalized diamine, 1,3-bis ((4-amino-2-(trifluoromethyl)phenoxylmethylene)-1,2,2-trimethyl cyclopentane (BAFMT), which was derivated from natural-(D)-camphor via multi-step process. The influence of the presence of the alicyclic and fluorinated structure on the general properties of the polymers was systematically investigated in terms of optical, thermal and mechanical properties, solubility and hydrophobicity, rendering the general structure–properties relationships for the FPI-x. Compared with the analogous control aromatic polyimide NPI-x, FPI-x shows better solubility, improved optical transparency, lower moisture absorption and surface energy, owing to the presence of the fluorine-containing group and alicyclic structure in the polymer chain. Although presenting a slight decrease as compared with NPI-x, the good thermal stability of polyimide was retained on the large in the fluorinated alicyclic-functionalized polymer FPI-x, with Tg ranging in 197–233 °C and Td5 ranging in 374–420 °C. A particular research emphasis were placed on employing the dielectric relaxation technique to study the dielectric constant (ε′), dielectric loss (ε″) and electric modulus (M″) of the fluorinated alicyclic-functionalized polyimide film FPI-4 and its control sample NPI-4. The observed dielectric relaxations have been fully studied by integrating the contributions of the specific structure and functional groups. It is revealed that the presence of fluorinated alicyclic-functionalized group endows FPI-4 with lower dielectric constant ε′ (2.88 at 1 MHz and 25 °C) and dielectric loss ε″ (0.0058 at 1 Hz and 25 °C) than NPI-4 (3.49 and 0.0084) and commercial Kapton HN (3.19 and 0.006) with the same measurement frequency and temperature.

Interaction of Silica Nanoparticle/Polymer Nanocomposite Cluster Network Structure: Revisiting the Reinforcement Mechanism

The understanding of nanoparticle–polymer interaction is a key element to demystify the structure–property relationship for nanocomposites. The clusters composing poly(acrylamide) (PAM) grafted from silica nanoparticles (SNPs) were prepared according to the developed synthetic platform and analyzed by transmission electron microscopy and dielectric relaxation analysis. The morphological evolution of clusters was observed and correlated to the mechanical behaviors of nanocomposites. Dynamic dielectric analysis was conducted to examine the nature of the constrained polymer region in view of a reinforcement mechanism. The modulus enhancement of the nanocomposite hydrogels was found to correlate with the volume of constrained polymer chains, and a constrained region model for SNP/polymer nanocomposites was proposed. The strong interactions between SNPs and polymer chains affect the modulus of the nanocomposites that was predicted by the percolation model and contributed to the mechanical reinforcement. The interplay between filler–polymer interaction and network rearrangement during the deformations should be considered to propose the reinforcement mechanism.

Comparative study of the dielectric properties of natural‐fiber–matrix composites and E‐glass–matrix composites

AbstractIn this work, we undertook a comparative study of the dynamic dielectric analysis of two composites: natural‐fiber‐reinforced unsaturated polyester (NFRUP) and E‐glass‐mat‐reinforced unsaturated polyester (EGMRUP). In both composites, two common relaxation processes were identified, the first of which was the α‐mode relaxation associated with the glass transition of the matrix. The second one was associated with conductivity that occurred because of the carriers' charge diffusion and was observed at temperatures above the glass transition and at low frequencies. However, the interfacial or Maxwell–Wagner–Sillars polarization was noticed only in the NFRUP composite. This dielectric study also revealed that compared to E‐glass fibers, natural fibers enhanced the thermal insulation in the composite. Also, the study of the fiber adhesion in the matrix with scanning electron microscopy, differential scanning calorimetry, and tensile testing revealed a great compatibility of the fibers with the matrix in both composites. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013

Influence of matrices chemical nature on the dynamic mechanical and dielectric properties of rubber composites comprising conductive carbon black

The study presents the effect that elastomeric matrices different in their chemical nature (a non-polar and crystallizing natural rubber and a polar and non-crystallizing acrylonitrile-butadiene rubber) have upon the dynamic mechanical and dielectric properties of the composites comprising different amounts of conductive carbon black. Dynamic mechanical thermal analysis (DMTA) and Dielectric thermal analysis (DETA) are the techniques used for studying the structure-properties relationships of the composites. The experimental results show that the matrices studied and their specific properties have a great impact upon both the dynamic mechanical and dielectric parameters of the composites based on them. The chemical nature, structure and specific characteristics of the matrix affect the storage modulus, glass transition temperature, elasticity behavior, high-elasticity, energy dispersion, dielectric permittivity and DETA tan δ of the composites investigated. The matrix effect dominates at lower filler amounts and determines the properties of the composites.