Investigation of the dielectric,mechanical, and thermal properties of noncovalent functionalized MWCNTs/polyvinylidene fluoride (PVDF) composites

To improve the dispersion of multi‐walled walled carbon nanotubes (MWCNTs) and investigate the effect of dispersant for MWCNTs functionalization on the dielectric, mechanical, and thermal properties of Polyvinylidene fluoride (PVDF) composites, two different dispersants (Chitosan and TritonX‐100) with different dispersion capability and dielectric properties were used to noncovalently functionalize MWCNTs and prepare PVDF composites via solution blending. Fourier transform infrared, X‐Ray diffraction, and Raman spectroscopy indicated that TritonX‐100 and Chitosan were noncovalent functionalized successfully on the surface of MWCNTs. With the functionalization of Chitosan and TritonX‐100, the dispersion of MWCNTs changed in different extent, which was investigated by dynamic light scattering and confocal laser scan microscopy. The dielectric, mechanical, and thermal properties of PVDF composites were also improved. Meanwhile, it was also found that the dielectric properties of PVDF composites are closely related to the dielectric properties of dispersant. High dielectric constant of dispersant contributes to the grant dielectric constant of PVDF composites. The mechanical and thermal properties of MWCNTs/PVDF composites largely depend on the dispersion of MWCNTs in PVDF, interfacial interactions and the residual solvent. Copyright © 2016 John Wiley & Sons, Ltd.     

Dielectric and dynamic mechanical relaxation studies on poly(aryl ether ketone)s

The relaxation behavior of four amorphous poly(aryl ether ketone)s was investigated using dielectric relaxation spectroscopy and dynamic mechanical analysis. The temperature dependence of the relaxation times of the glass transition process and the cooperative nature of this process were unaffected by changes in polymer structure. The temperature location of the loss peaks for all polymers progressed smoothly between the low frequency of the mechanical measurements and the higher frequencies of the dielectric probe. Differences were observed in mechanical activation energy and dielectric relaxation strength for one polymer which contained a significant concentration of meta linkages, compared with the para-linked polymers, while relaxation broadness was generally greater in the dynamic mechanical mode. Changes in chemical structure had little effect on the shape, intensity, and location of the β-relaxation peak, the main observation being that the Arrhenius activation energy measured by dynamic mechanical analysis was significantly higher than that calculated from the dielectric data. The dielectric β-relaxation was sensitive to absorbed moisture. © 1998 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 36: 851–859, 1998     

聚全氟乙丙烯的转变

<正> 聚全氟乙丙烯(F_s-46)是四氟乙烯(TFE)与六氟丙烯(HFP)的共聚物。McCrum用扭摆法测得α和β转变与HFP含量有关。Eby等用超声波法发现γ松弛也与HFP含量有关。 本文用动态力学法发现HFP含量对α、β、γ转变都有影响。用介电方法得到了α、γ、δ三个转变峰。δ峰属于端基运动,Eby等认为是—CF_2H基运动;我们从红外光谱图中检测到—COOH基的存在,认为与—COOH基运动也有关。     

Anisotropy of mechanical and dielectric relaxation in oriented poly(ethylene terephthalate)

The anisotropy of the α and β relaxations in oriented poly(ethylene terephthalate) has been studied by dynamic mechanical and dielectric relaxation measurements. The α relaxation shows considerable mechanical anisotropy but gives rise to an isotropic dielectric process. The β relaxation, on the other hand, shows pronounced dielectric anisotropy but very little mechanical anisotropy. The implication of these results with regard to possible interpretations of the relaxations are discussed.     

An acoustic dielectric and mechanical spectrometer

In this report, the dielectric constant of glycerol solutions (0-70% (w/w)) and the mechanical transitions of poly(2-hydroxylethyl methacrylate-co-methacrylic acid) films (600-800 nm, 1.5-10 mol% cross-linker) have been investigated by the magnetic acoustic resonance sensor (MARS), which is an electrode-free acoustic sensor and operates over a continuous frequency spectrum (6-200 MHz). When a glycerol solution was loaded, the response of the MARS decayed exponentially as the operating frequency was increased. The decay rate against frequency as a function of the glycerol concentration reflects the change of the dielectric property of the glycerol solutions. In addition, mechanical relaxation of the poly(2-hydroxylethyl methacrylate-co-methacrylic acid) film has been observed on the MARS and the corresponding viscoelastic transition frequency has been estimated. The viscoelastic transition frequency increased as the polymer was more highly cross-linked. The MARS system behaved as a dielectric and mechanical spectrometer, monitoring the electrical and mechanical properties of viscoelastic materials or on the solid-liquid interfaces simultaneously, which has prospective application in studies of biomaterials, molecular interactions and drug deliveries.     

活性酯固化环氧树脂物性的研究

主要对活性酯固化环氧树脂的吸水性、高耐湿性、电气特性等方面进行了研究,同时也对其树脂极性、交联结构、分子链运动等方面也进行了研究．     

Dielectric and shear mechanical alpha and beta relaxations in seven glass-forming liquids

We present shear mechanical and dielectric measurements taken on seven liquids: triphenylethylene, tetramethyltetra-phenyltrisiloxane (Dow Corning 704 diffusion pump fluid), polyphenyl ether (Santovac 5 vacuum pump fluid), perhydrosqualene, polybutadiene, decahydroisoquinoline (DHIQ), and tripropylene glycol. The shear mechanical and dielectric measurements are for each liquid performed under identical thermal conditions close to the glass transition temperature. The liquids span four orders of magnitude in dielectric relaxation strength and include liquids with and without Johari-Goldstein beta relaxation. The shear mechanical data are obtained by the piezoelectric shear modulus gauge method giving a large frequency span (10(-3)-10(4.5) Hz). This allows us to resolve the shear mechanical Johari-Goldstein beta peak in the equilibrium DHIQ liquid. We moreover report a signature (a pronounced rise in the shear mechanical loss at frequencies above the alpha relaxation) of a Johari-Goldstein beta relaxation in the shear mechanical spectra for all the liquids which show a beta relaxation in the dielectric spectrum. It is found that both the alpha and beta loss peaks are shifted to higher frequencies in the shear mechanical spectrum compared to the dielectric spectrum. It is in both the shear and dielectric responses found that liquids obeying time-temperature superposition also have a high-frequency power law with exponent close to -12. It is moreover seen that the less temperature dependent the spectral shape is, the closer it is to the universal -12 power-law behavior. The deviation from this universal power-law behavior and the temperature dependencies of the spectral shape are rationalized as coming from interactions between the alpha and beta relaxations.     

A study on dielectric characteristics of fluorinated polyimide thin film

In this work, the effects of fluorination of polyimide thin films on surface and dielectric characteristics were studied using X-ray photoelectron spectroscopy (XPS) and dielectric spectrometry, respectively. The thermal and mechanical properties of the film were characterized by thermogravimetric analysis (TGA) and tensile strengths, respectively. The fluorine content of the polyimide thin film was increased with increasing treatment concentration, resulting in decreasing dielectric constant of the film. It was found that the replacement of fluorine led to the decrease of the local electronic polarizability of polyimide, or to the increase of the free volume, which can be attributed to the relatively large size of fluorine. Nevertheless, the fluorination did not significantly affect thermal or mechanical properties of the polyimide film under mild conditions in this system.     

Dependence of the dielectric constant on the structure of extruded polyvinylidene fluoride films

The structure of extruded polyvinylidene fluoride films obtained at different die drawing ratios and melt temperatures was studied by X-ray scattering, differential scanning calorimetry, and gravimetry. Their dielectric constant and mechanical properties were examined. The influence exerted by the structure of the amorphous phase and by the molecular weight of the polymer on the dielectric constant of the samples was revealed.     

Activation parameters associated with the β relaxation of poly(cyclohexyl acrylate)

The interpretation of the mechanical and dielectric β relaxations of poly(cyclohexyl acrylate) by the coupling scheme suggests that the dielectric relaxation process is more complex than the mechanical one, contrary to what occurs in the glass–rubber relaxation. The distribution of activation energies for the dielectric process, obtained from isochronal and isothermal loss curves, increases with temperature and frequencies. The determination of the distribution of the activation-free energy indicates a distribution of the activation entropy for both the mechanical and dielectric β process, suggesting that a distribution of preexponential factors in the Arrhenius equation also exists. © 1992 John Wiley & Sons, Inc.     

Water sorption and electrical/dielectric properties of organic-inorganic polymer blends

Organic-inorganic polymer blends (OIPB) were obtained by reaction of organic and inorganic oligomers. The organic oligomer was synthesized with 2,4-toluene diisocyanate (TDI) and oligooxypropylene glycols (OPG) with various molecular weights (MW). The inorganic component was a water solution of sodium silicate. The OIPB obtained are hydrophilic and have great water sorption ability (the relative weight of sorbed water reaches 2000 %). The kinetics of water sorption and the changes of electrical conductivity during sorption were studied. Sorption ability, and mechanical, electrical and dielectric properties of OIPB depend on molecular weight of OPG: conductivity increases with increasing MW, whereas the sorption ability correlates with the mechanical properties. The influence of the inorganic phase content on the electrical and dielectric properties was studied as well.     

Theoretical investigation of polymer molecular structure influence on dielectric properties and mechanical properties

Triboelectric nanogenerator (TENG) technologies have explosive development in the field of energy harvesting and self-powered sensing. As the key element of triboelectric devices, dielectric polymers have obtained much attention in recent years. The dielectric properties of polymer determine the output performance of TENG. In this paper, we take silicone rubber as an example of dielectric polymers, to study the properties of molecular structure influence on the dielectric properties and mechanical properties by the molecular dynamics simulation method. The free volume fraction, dielectric constant, and mechanical properties of silicone rubbers with different branch chains were calculated. The dielectric constant is highly related to the free volume distribution and the dipole moments of silicone rubbers with different amounts of branch chains. For fewer branch chains silicone rubber, the free volume distribution contributes most to the dielectric constant; for more branch chains silicone rubber, the dipole moment dominates the dielectric constant. Therefore, the silicone rubber ratio has a great influence on the dielectric constant of silicone rubber. With the increase of temperature, the dielectric constant of 2-chain silicone rubber increases at first and then decreases, and the maximum value is obtained near 300 K. Therefore, it is necessary to control the temperature when silicone rubber is used as a dielectric material. This work can be a guide for improving the dielectric properties of silicone rubber, and it provides a new approach to the optimal design of high-performance triboelectric nanogenerators.     

Properties of glass-fiber reinforced composites based on liquid diglycidyl ether of bisphenol-c-epoxy resin

Glass-fiber reinforced epoxy composites were fabricated from the matrix resin liquid diglycidyl ether of bisphenol-C (DGEBC) using various amines as curing agents with and without fortifier (20 phr). The epoxy laminates were evaluated for their mechanical properties, such as flexural strength, interlaminar shear strength (ILSS), tensile strength and shore-D hardness. Dielectric properties, such as the dielectric constant, tan δ, dielectric loss and the resistivity of the laminated samples, were measured. The effect of the chemical reagents on the mechanical properties (i.e. flexural strength, lLSS) was also studied.     

Simultaneous monitoring of viscoelastic and dielectric properties of curing epoxy resins using a vibrating electrode

Both dielectric and mechanical dynamic analysis can characterize the curing of epoxy resins. As the reproducibility of this process is poor, data from separate measurements cannot be compared. To allow for a simultaneous measurement of frequency-dependent viscoelastic (0.5–8 kHz) and dielectric (50–800kHz) properties, a vibrating electrode is used. The curing measurements of four different epoxy-amine systems show a frequency-dependent drop in both the dielectric and compliance real parts. Higher frequencies are sensitive to the relaxation of smaller molecules, hence, the step due to vitrification occurs first at higher frequencies. Accompanied by a loss maximum the dielectric step shifts down over four decades to a lower frequency region and appears eventually in the mechanical spectrum. The simultaneous investigation reveals that the dielectric and the longitudinal compliance function have almost the same frequency dependent reaction kinetic behavior. The mechanical time behavior can be extrapolated in the frequency domain by a power law to obtain the dielectric time parameters and vice versa.     

Correlation between static mechanical properties of starch-glycerol materials and low-temperature relaxation

Mechanical, calorimetric, dynamic mechanical and dielectric properties were measured in starch and amylose films plasticized by different glycerol contents. Low-temperature relaxation was found to be highly dependent on plasticizer level and related to unusual mechanical properties.     

Fabrication of exfoliated graphite reinforced silicone rubber composites - Mechanical,tribological and dielectric properties

The effect of exfoliated graphite (EG) on the mechanical, tribological and dielectric properties of the silicone rubber (QM) composites has been systematically investigated and analysed. Morphological analysis of the composites helps to understand the interfacial interaction between the filler and the rubber matrix as well as wear mechanism respectively. An enhancement in the mechanical, tribological and dielectric properties was observed with an increase in filler loading and better performance was observed at 7 phr of filler loading. The improvement in performance is attributed to the better interaction between the QM chains and the EG layers as evident from the AFM and TEM analysis. It is also evident from the Kraus plot which supports the reinforcing effect of EG in QM matrix.     

The effects of solvent screening in quantum mechanical calculations in protein systems

We report on an implementation of quantum mechanical density functional calculations carried out in a dielectric medium. The dielectric medium is introduced by integrating the solution of the Poisson-Boltzmann equations into the density functional calculation. The calculations are carried out for a simple amide in vacuum, in the field of an ion, and in the ion field in several dielectric environments. The environment was constructed to include a low dielectric interior embedded in a high dielectric continuum of dielectric 80 (corresponding to aqueous solution). The energies and electron densities of formamide in the ion field were calculated at various configurations in this system, including at the low dielectric–high dielectric interface. The systems were designed to simulate situations which are similar to those that occur in proteins (i.e., the protein constitutes the low dielectric medium surrounded by aqueous solution). The system mimics situations in which charges in such proteins located in various regions interact with other parts of the protein and with ligands which mainly bind to the surface. © 1994 by John Wiley & Sons, Inc.     

Phase and state transition effects on dielectric, mechanical, and thermal properties of polyols

The present study investigated the glass transition, crystallisation and melting behaviour of erythritol, xylitol, and glucitol (sorbitol) using dielectric analysis (DEA), differential scanning calorimetry (DSC), and dynamic mechanical analysis (DMA). Sorbitol and xylitol were plasticised by water and their glass transition temperatures decreased when water content was increased. Erythritol crystallised rapidly, and its water plasticisation behaviour could not be determined. Melting of the crystalline polyols occurred at their specific melting temperatures. Melts of erythritol and xylitol crystallised on recooling and no glass transition was apparent on reheating. Quench cooled sorbitol melt remained amorphous and showed a glass transition on reheating. Glass transition and crystallisation were apparent in the DSC thermogram and the dielectric and the dynamic mechanical spectra of mixtures of amorphous and crystalline xylitol.     

Effect of thermal curing on the properties of thin films based on benzophenonetetracarboxylic dianhydride and 4,4′-diamino-3,3′-dimethyldiphenylmethane

The processing of polyimide films from polyamidic acid solutions involves the simultaeous loss of solvent and chemical conversion, and may imply structural reorganization such as orientation or crystallization. The effect of thermal treatment on the thermal, mechanical and dielectric properties of polymer films based on benzophenonetetracarboxylic dianhydride and 4,4’-diamino-3,3’-dimethyl diphenylmethane have been investigated. The thermal treatment of polyamidic acid at different temperatures led to compounds with different degree of imidization; it turned out that the imidization process took place with high speed until 240 °C and then remained constant. The dynamic mechanical analysis (DMA), contact angles, and dielectric measurements revealed that the storage modulus and contact angles increased with increasing of curing temperature while the dielectric constant decreased.     

Investigation of the effect of calcination temperature on HMDS-treated ordered mesoporous silica film

To reduce signal delay in ultra-large-scale integrated circuits, an intermetal dielectric with low dielectric constant is required. Ordered mesoporous silica film is appropriate for use as an intermetal dielectric due to its low dielectric constant and superior mechanical properties. To reduce the dielectric constant, an ordered mesoporous silica film prepared by a tetraethoxysilane/methyltriethoxysilane silica precursor and Brij-76 block copolymer was surface-modified by hexamethyldisilazane (HMDS) treatment. HMDS treatment substituted OH with Si(CH₃)₃ groups on the silica surface. After treatment, ordered mesoporous silica films were calcined at various calcination temperatures, and the calcination temperature to obtain optimal structural, electrical, and mechanical properties was determined to be approximately 300 °C.