Effect of different forms of poly o‐toluidine/poly vinyl chloride composites on dielectric properties in the microwave field

In this paper we report the preparation and dielectric properties of poly o‐toluidine:poly vinyl chloride composites in pellet and film forms. The composites were prepared using ammonium persulfate initiator and HCl dopant. The characterization is done by TGA and DSC. The dielectric properties including dielectric loss, conductivity, dielectric constant, dielectric heating coefficient, absorption coefficient, and penetration depth were studied in the microwave field. An HP8510 vector network analyzer with rectangular cavity resonator was used for the study. S bands (2–4 GHz), C band (5–8 GHz), and X band (8–12 GHz) frequencies were used in the microwave field. Comparisons between the pellet and film forms of composites were also included. The result shows that the dielectric properties in the microwave field are dependent on the frequency and on the method of preparation. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 2253–2260, 2007     

微波驱动咪唑类聚离子液体/聚乙烯醇形状记忆材料

结合微波驱动原理、聚离子液体（PIL）及形状记忆聚合物的结构特性,目的是设计合成完全基于聚合物、能在微波驱动下快速回复的聚离子液体/聚乙烯醇（PVA）形状记忆复合材料。首先合成了乙烯基咪唑功能性离子液体单体（[ViEtIm][BF₄],ILM）,之后在含有戊二醛的PVA溶液中对ILM进行原位聚合生成PIL,将PIL引入到交联PVA中,形成聚乙烯基咪唑PIL/PVA形状聚合物复合材料（SMPC）。用核磁对ILM和PIL的结构进行了表征,证明了所合成目标化合物的结构准确性。介电性能测试结果显示PIL/PVA有较高的介电常数和介电损耗,当P[ViEtIm][BF₄]含量从0增加到30%时PIL/PVA复合材料的介电损耗因子呈增大趋势,可见PIL是一种有效的微波吸收介质。弯曲法测试结果表明该复合材料在微波驱动下具有很好的形状记忆效应,所有复合材料的形变固定率都接近100%且形变回复率都高达80%以上,且PIL的含量和微波输出功率的大小对材料回复率和回复时间有显著影响。140 W的微波足以驱动PIL/PVA SMPC发生回复,280 W下40 s内可以完成,微波功率增大到420 W时SMPC在20 s内可回复到起始形状。     

Melt‐intercalation nanocomposites with fluorinated polymers and a correlation for nanocomposite formation

Various fluorinated polymers were investigated to produce polymer nanocomposites with special clays. Natural and organically treated montmorillonite clays were melt‐compounded with the polymers. Characterization by wide‐angle X‐ray scattering and transmission electron microscopy showed the separation of montmorillonite layers and the formation of polymer nanocomposites. Organically treated montmorillonite clay dispersed in poly(vinylidene fluoride) and various vinylidene fluoride copolymers and formed nanocomposites. Natural and organophilic clays were not well dispersed in other fluorinated copolymers and polyethylene. A correlation was developed for the formation of polymer–clay nanocomposite structures in chlorinated and fluorinated polymers in terms of the dielectric constant. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 1061–1071, 2004     

Structural and dielectric studies of amorphous and semicrystalline polymers blend‐based nanocomposite electrolytes

The solid polymeric nanocomposite electrolyte (SPNE) films based on the blend of amorphous poly(methyl methacrylate) (PMMA) and semicrystalline poly(ethylene oxide) (PEO) (PMMA:PEO = 80:20 wt %) doped with lithium perchlorate (LiClO₄) salt and montmorillonite (MMT) clay nanofiller were prepared by classical solution cast, ultrasonic assisted solution cast and ultrasonication along with microwave irradiated solution cast followed by melt‐pressing methods. The X‐ray diffraction study of these electrolytes revealed the amorphous behavior with intercalated MMT structures. The suppressed crystallinity of PEO in the blend electrolyte complexes confirmed the existence of single discrete PEO chains confined within the PMMA domains. The dielectric relaxation spectroscopy of these materials was performed over the frequency range 20 Hz to 1 MHz, at ambient temperature. The presence of a singular relaxation peak in the loss tangent and electric modulus spectra of these electrolytes confirms a coupled cooperative chain segmental dynamics of the blend polymer owing to their miscible amorphous morphology. The behavior of transient complexes formed between the polymers functional groups, lithium cations and the intercalated MMT nanoplatelets was explored. The ambient temperature ionic conductivity of these electrolytes depends on the structural dynamics and the sample preparation methods. It is revealed that the presence of PEO in the PMMA matrix mainly governs the structural, dielectric, and ionic properties of these SPNE films. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41311.     

Polyurethane curing by a pulsed microwave field

The complete study of the crosslinking of polyurethane resins by means of a pulsed microwave field has been made, in order to describe the energy transfer processes in polymer films and to optimize the transfer efficiency. Experimental data show the energy transfer can be strongly enhanced by using specific pulse repetition frequencies which correspond to dielectric relaxation of polar structural elements in polymers. Moreover, the hardness of cured films can be also correlated with this pulse frequency specificity.     

Polymer compatibility: Ternary blends of poly(vinylidene chloride-co-vinyl chloride), poly(vinyl chloride) and poly(acrylonitrile-co-butadiene)

Mixtures of two compatible polymers, poly(vinyl chloride) and poly(acrylonitrile-co-butadiene) containing 40 percent acrylonitrile, can be compatible with poly(vinylidene chloride-co-vinyl chloride), which is incompatible and partially compatible respectively with these two polymers. The crystalline melting temperature and relative heat of fusion of poly(vinylidene chloride-co-vinyl chloride) in blends are higher than those in the pure component. This is attributed to greater ordering of the polymer chains in the crystalline phases of the blends. Replacing the rubber by poly(acrylonitrile-cobutadiene) containing 30 percent acrylonitrile, shows that these three polymers, in which each pair is incompatible or at most partially compatible, also form compatible ternary blends. The crystalline melting temperature is higher and relative heat of fusion lower than those in the pure component. This is attributed to dissolving of parts of the polymer chains originally located in the crystalline phases in the amorphous phases of the blends.     

Core-shell structured BaTiO3@SiO2@PDA for high dielectric property nanocomposites with ultrahigh energy density

Flexible nanocomposite dielectrics with high dielectric constant and discharge energy density have broad application prospects in the field of energy storage. However, dielectrics with high dielectric constant tend to have a high dielectric loss. Herein, we prepared a dielectric composite material with ultra-high discharge energy density by modifying the interface between nanoparticles and poly(vinylidene fluoride-co-hexafluoropropylene) (P[VDF-HFP]). After coating a shell of insulating amorphous SiO₂ (~7 nm) outside the barium titanate (BT), the electric field concentration and current density inside BT particles can be significantly reduced. In addition, coating the SiO₂ shell with a polydopamine (PDA) shell (~7 nm) not only enhances the interface interaction between the nanoparticles and the polymer matrix, but also can form lots of microcapacitors in the composite. As a result, an ultra-high discharge energy density of 13.78 J/cm³ at the expense of relatively inconspicuous efficiency (~59.8%) in the BT@SiO₂@PDA/P (VDF-HFP) with 2.5 wt% loading has been achieved under 460 kV/mm. This is mainly attributed to the increases of dielectric constant from 12.1 to 14.2 and the relatively low dielectric loss (0.086) at 100 Hz. Moreover, compared with the pure P (VDF-HFP) (400 kV/mm), the breakdown voltage of the composite with 2.5 wt% loading is surged to 460 kV/mm, which benefited from the hindrance of nanoparticles on carrier migration at low content. This work has realized a thin-film dielectric with ultra-high discharge energy density through a novel design of the nanoparticle structure, providing a theoretical direction for the development of polymer dielectric capacitors.     

Cleaner preparation of poly(vinylidene fluoride)/barium titanate composites: Thermal,mechanical, and dielectric properties and relaxation dynamics

Traditional polymer composite preparation techniques often employ organic solvents, which can damage the environment, to disperse inorganic fillers. In this article, classic nanocomposites with poly(vinylidene fluoride) (PVDF) polymer matrices and BaTiO₃ nanoparticle (BTP) fillers were created by a clean method combining planetary ball milling with an ultracentrifugal mill and then hot pressed into thin films. The microstructures, properties and relaxation dynamics of the thin films were characterized and analyzed. Scanning electron microscopy results demonstrated that BTP was homogeneously dispersed in the PVDF matrix. The thermal, mechanical, and dielectric properties were comparable to those of composite films prepared by solution mixing. Dielectric analysis revealed that the dielectric constant of the thin films reached 14 (10⁴ Hz) when the volume fraction of BTP was 30%; however, the dielectric loss was 0.1 (10⁴ Hz). Additionally, the dielectric loss spectra fitted with the Havriliak−Negami (H−N) and Vogel Fulcher equations were employed to analyze the relaxation dynamics of the nanocomposites. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47254.     

Exceptional dielectric properties of chlorine-doped graphene oxide/poly (vinylidene fluoride) nanocomposites

Herein, we report a facile method to significantly enhance the dielectric performance of reduced graphene oxide-based polymer composites. Addition of thionyl chloride into graphene oxide (GO) dispersion induces synergistic modifications of the structure, chemistry, charge carrier density and electrical conductivity of GO, as well as the interfacial interaction and phase of the surrounding matrix in the poly (vinylidene fluoride) (PVDF) composite. The composites reinforced with a very low reduced chlorinated GO (Cl-rGO) content of 0.2 vol% deliver an exceptional dielectric constant of 364 with a moderate dielectric loss of 0.077 at 1 kHz. These values are well contrasted with the corresponding properties of the neat PVDF polymer with a constant of 28 and a loss of 0.0029. Synergistic effects arising from chlorination are identified, including the much enhanced electrical conductivity of Cl-GO sheets by more than 3 orders of magnitude through introducing charge-transfer complexes, the improved interfacial interactions between the fillers and the PVDF matrix through hydrogen bonds, and the transformation of PVDF to β-phase with an inherently high dielectric constant due to dipolar interaction. The comparison with the literature data confirms superior dielectric performance of the present Cl-rGO/PVDF composites.     

All-organic Poly(butyl methacrylate)/Poly(vinylidenefluoride-trifluoroethylene) Dielectric Composites with Higher Permittivity and Low Dielectric Loss for Energy Storage Application

With the rapid development of electronic industry and technology, there are increasingly stringent requirements on dielectric materials with higher permittivity, lower loss, and enhanced breakdown field. Since single dielectric material cannot meet the demands of industrialization, polymer-based dielectric materials with better quality have been widely applied. This study focused on a poly(butyl methacrylate/poly(vinylidene fluoride-trifluoroethylene) dielectric composite thin film, which were prepared by solution casting method. X-ray diffraction and differential scanning calorimetry data indicated that introducing poly(butyl methacrylate) led to increase in the crystallinity. The result of scanning electron microscopy showed the good compatibility between poly(vinylidene fluoride-trifluoroethylene) and poly(butyl methacrylate). Besides, the dielectric film remained good mechanical property. The dielectric properties were studied as a function of filler content and frequency. The results showed that the permittivity was as high as 13.3, while the breakdown field was 322?MV m^?1 when the fraction of poly(butyl methacrylate) was 10%. Blending poly(butyl methacrylate) improved the dielectric performance of the poly(vinylidene fluoride-trifluoroethylene).     

Dynamics in complex systems: Dendrimer-polymer blends in electric and mechanical fields

An investigation was carried out on the molecular dynamics of blends composed of poly(amidoamine) (PAMAM) dendrimers with ethylenediamine core and amino surface groups (generations 0 and 3) and three linear polymers: poly(propylene oxide) - PPO and two block copolymers, poly(propylene oxide)/poly(ethylene oxide) - PPO/PEO with different mole ratios: 29/6 (amorphous) and 10/31 (crystalline). The results were generated over a broad range of frequency and temperature by Dielectric Relaxation Spectroscopy (DRS) and Dynamic Mechanical Spectroscopy (DMS). Dielectric spectra of dendrimers in the PPO matrix reveal a decrease in the time scale of normal and segmental relaxation with increasing dendrimer concentration. In the amorphous blends with 29PPO/6PEO matrix, no effect of concentration on the time scale of normal and segmental processes was observed. But in the crystalline blends with 10PPO/31PEO matrix, relaxation time increases with increasing dendrimer concentration. Results acquired by DRS and DMS were contrasted and the obtained relaxation times were found to be in excellent agreement. A detailed analysis of the effect of generation and concentration of dendrimers, hydrophilicity and morphology of the polymer matrix and temperature on the molecular origin, the shape of the relaxation spectra, the dielectric relaxation strength and the frequency location for the maximum loss in dendrimer-polymer blends is provided.     

复合钙钛矿陶瓷的结构与微波介电性能

介绍了复合钙钛矿化合物结构的本质特征，讨论了钙钛矿结构对微波介质陶瓷材料的介电性能（介电常数、介质损耗、频率温度系数）的各种影响因素。     

高性能陶瓷微波介质材料

微波介质陶瓷可使微波通信和其他微波设备小型化,是有良好发展前景的一种介电材料。目前已经研制出许多具有高介电常数、高品质因数、低介质损耗及小谐振频率温度系数的优质微波介质陶瓷。本文综述近年来微波介质陶瓷在制备工艺、改良介电性能及应用方面的最新进展,并指出了今后的研究方向。     

Dielectric Properties of MoS2 and Pt Catalysts: Effects of Temperature and Microwave Frequency

The effects of temperature and microwave frequency on the dielectric properties of MoS₂ and Pt catalysts together with an aluminum oxide support were investigated. Dielectric constants and dielectric loss factors were measured in a temperature range of 200-800 °C by a cavity resonator technique with a cylindrical copper cavity resonating in TM_0n0 modes (n = 1, 2, ... ,5), which corresponded to frequencies of 0.615, 1.413, 2.216, 3.020, and 3.825 GHz.     

Improved dielectric properties of PDCs-SiCN by in-situ fabricated nano-structured carbons

In order to enhance dielectric properties of polymer derived SiCN ceramics (PDCs-SiCN), nano-structured carbons were in-situ fabricated in PDCs-SiCN by pyrolysis of ferrocene-modified polysilazane. Microstructure evolutions, dielectric and microwave absorption properties of PDCs-SiCN decorated with nano-structured carbons were investigated. Nano-structured PDCs-SiCN ceramics are composed of carbon nanowires as well as interpenetrating graphene-like free carbons, SiC nano-crystals, Si₃N₄ nano-crystals and amorphous SiCN. Relative complex permittivities of nano-structured PDCs-SiCN increase with increasing ferrocene contents and annealing temperatures. Free carbons in PDCs-SiCN play a dominating role on the improved dielectric properties. Polarization loss is the primary dielectric loss. Loss tangent of PDCs-SiCN exceeding 0.7 is obtained when free carbons are only 2.57% in weight. Nano-structured PDCs-SiCN exhibit good microwave absorption property. The reflectivity is smaller than −14 dB in the whole X band when material is composed of both impedance and microwave absorption materials.     

The effect of modifier contents of polyvinyl pyrrolidone on the enhanced dielectric and microwave absorbing properties of multiwalled carbon nanotubes

Polyvinyl pyrrolidone (PVP) polymers were used as non‐covalent modifiers to modify the surface of multi‐walled carbon nanotubes (MWNTs) by ultrasonic dispersion method. The transmission electron microscope results suggest that a layer of polymers is wrapped on the surface of MWNTs, and the thickness is about 2.5 nm. The addition of PVP helps to facilitate uniform distribution of MWNTs and increases the interfacial multipoles formed between PVP and MWNTs, which plays an important role in the regulation of the dielectric parameter and the enhancement of the microwave absorbing properties. The effects of PVP loadings and thickness of PVP/MWNTs hybrids on the dielectric parameter of MWNTs are investigated. The microwave absorbing properties are calculated from the dielectric constants. The results show that the maximum reflection loss is ?26.27 dB at 7.8 GHz while the loading of PVP on MWNTs is 8.0 wt % with a thickness of 3.0 mm. These results suggest that the PVP contents and absorber thickness are important factors for the improvement of dielectric loss and microwave absorption properties of MWNTs. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 41007.     

Dielectric and thermal response of poly[(vinylidene chloride)‐co‐acrylonitrile]/poly(methyl methacrylate) blend membranes

Poly(methyl methacrylate) was mixed with poly[(vinylidene chloride)‐co‐acrylonitrile] (Saran‐F) and lithium perchlorate in tetrahydrofuran to make polymer blend systems. Solvent‐free membranes with various blend ratios were prepared using a solution casting technique. Impedance analysis was used to study the electrical response of the polymer membranes, which shows that the 50:50 wt% blend ratio polymer membrane has a low bulk resistance and high dielectric constant at room temperature and hence high ionic conductivity. The dielectric behaviour was analysed using dielectric permittivity and electric modulus of the samples. The conductance spectra follow the universal power law variation. Structural analysis confirms the amorphous nature and functional group analysis confirms the miscibility. The decomposition temperature of the membranes was determined using thermogravimetric analysis. © 2014 Society of Chemical Industry     

Morphological,structural, dielectric and electrical properties of PEO–ZnO nanodielectric films

The morphological, structural, dielectric and electrical properties of aqueous solution-cast prepared poly(ethylene oxide)–zinc oxide (PEO–ZnO) nanocomposite films have been investigated as a function of ZnO nanoparticle concentrations up to 5 wt%. Scanning electron microscopy (SEM) images of these films show that the morphology of pristine PEO aggregated spherulites changes into fluffy, voluminous and highly porous with dispersion of ZnO nanoparticles into the PEO matrix. X-ray diffraction (XRD) study confirms that the crystalline phase of PEO greatly reduces at 1 wt% ZnO, and it again increases gradually with further increase of ZnO concentration. The dielectric relaxation spectroscopy (DRS) over the frequency range 20 Hz–1 MHz reveals that the real part of complex dielectric permittivity at audio frequencies decreases non-linearly whereas it remains almost constant at radio frequencies for these polymeric nanocomposites. Dispersion of nanosize ZnO particles into the PEO matrix reduces the values of dielectric permittivity which also exhibits a correlation with the dispersivity of ZnO nanoparticles. The relaxation peaks observed in the dielectric loss tangent and electric modulus spectra reveal that the electrostatic interactions of nanoscale ZnO particles with the ethylene oxide functional dipolar group of PEO monomer units decrease the local chain segmental dynamics of the polymer. Real part of ac conductivity spectra of these films have been analyzed by power law fit over the audio and radio frequency regions, respectively, and the obtained dc conductivity values for these regions differ by more than two orders of magnitude. The temperature dependent relaxation time and dc conductivity values of the nanodielectric material obey the Arrhenius relation of activation energies and confirm a correlation between dc conductivity and PEO chain segmental motion which is exactly identical to the characteristics of solid polymer electrolytes. Results imply that these nanocomposite materials can serve as low permittivity flexible nanodielectric for radio frequency microelectronic devices and also as electrical insulator for audio frequency operating conventional devices in addition to their suitability in preparation of solid polymer electrolytes.     

Comparison of gas permeation in vinyl and vinylidene polymers

The gas transport properties of several simple vinyl and vinylidene polymers are compared to examine the effect of pendant group type (H, CH₃, F, Cl) and symmetry of placement. The literature contains extensive information about these polymers, which has been critically reviewed to obtain consistent data for interpretation of the effect of structure on gas permeability. The gas transport data available for many of these polymers are quite variable because of differences in additives, thermal history, and crystallinity. The values used here are from studies where the physical properties of the film were reported along with the transport data. The appropriate data were not available for poly(vinyl fluoride) or poly(vinylidene chloride). For poly(vinyl fluoride), permeability measurements and thermal analysis were done to supply this information. Results for poly(vinylidene chloride) were obtained by extrapolation of copolymer permeation properties. Estimates of the permeability of oxygen in the amorphous phase of each polymer are discussed in terms of the estimated fractional free volume of that phase. In this way, the intrinsic effects of molecular structure on gas permeation exclusive of crystallinity effects have been evaluated.     

Effect of shell phase composition on the dielectric property and energy density of core-shell structured BaTiO3 particles modified poly(vinylidene fluoride) nanocomposites

Dielectric nanocomposites have attracted much attention due to their wide applications in electronics and electrical industry. Recently, incorporating core-shell nanoparticles into polymer matrix to improve the dielectric properties of nanocomposites has been widely reported. Tailoring the interfacial region between the polymer and the nanoparticles plays a crucial role in achieving the desired dielectric and energy storage properties of nanocomposites. However, the effect of shell structure in the interface region on the dielectric and energy storage properties is rarely studied. Based on this, core-shell BaTiO₃ nanoparticles with two different shell polymers, a “hard-soft” copolymer of methyl methacrylate and butyl acrylate (P[MMA-BA]) and a “hard” homopolymer of methyl methacrylate (PMMA), were prepared in this paper. The effect of core-shell BaTiO₃ nanoparticles with different shell structures on the dielectric and energy storage properties of poly(vinylidene fluoride) (PVDF) was investigated in depth. Due to the formation of a tight interfacial region between P(MMA-BA)@BT and PVDF matrix, P(MMA-BA)@BT/PVDF nanocomposites not only have low dielectric loss but also higher energy efficiency than PMMA@BT/PVDF nanocomposites. This study suggests a potential strategy that fabricating a “hard-soft” copolymer shell on BaTiO₃ surface can obtain desirable energy storage efficiency than the single “hard” shell structure in dielectric nanocomposites.