Dielectric properties of polymer/ceramic composites based on thermosetting polymers

Summary A series of thermosetting polymer/ceramic composites were prepared. Three kinds of thermosetting polymers, i.e. cyanate resin, bismaleimide resin, and epoxy resin, were used as matrixes, and BaTiO₃ particles were as fillers. The dielectric properties of these composites were investigated. Experimental data of the dielectric constants were fitted to several theoretical equations in order to obtain the best-fitting equations of the dielectric constants of these composites. The result indicates that the dielectric constants of composites all increase with the increase of BaTiO₃ content. Using bismaleimide resin and epoxy resin as matrixes, the dielectric losses both increase obviously as the amount of BaTiO₃ particles is increased, but the dielectric loss of cyanate/BaTiO₃ composite decreases. With the increase of the frequency, the variation ranges of the dielectric constant and dielectric loss of cyanate/BaTiO₃ composite are both the smallest. The predications of the effective dielectric constants by Lichterecker mixing rule are in good agreement with experiment data.     

Dielectric properties of polymer nanoparticle composites

Well-dispersed high dielectric permittivity titanium dioxide (TiO₂) nanoparticles were synthesized utilizing a block copolymer as a template. The nanoparticles were confined within microphase separated domains of sulfonated styrene-b-(ethylene-ran-butylene)-b-styrene (S-SEBS) block copolymers. A crosslinker (vinyltrimethoxysilane) was incorporated into the block copolymer matrices in order to decrease the dielectric loss from the free sulfonic acid groups. Dynamic mechanical analysis experiments confirmed that nanoparticles and crosslinker were confined within the crosslinked sulfonated styrene blocks and had no effect on the chain relaxation behavior of [ethylene-ran-butylene] blocks. Dielectric experiments showed that higher permittivity composites can thus be obtained with a significant decrease in loss tan δ (<0.01) when crosslinked with vinyltrimethoxysilane.     

Alkaline direct methanol fuel cell based on a novel anion-exchange composite polymer membrane

The anion-exchange composite polymer membrane based on quaterized poly(vinyl alcohol)/poly(epichlorohydrin) (designated as Q-PVA/PECH) was prepared by a solution casting method and a quaternization process. The characteristic properties of the Q-PVA/PECH anion-exchange composite polymer membranes were investigated by scanning electron microscopy, thermal gravimetric analysis, micro-Raman spectroscopy, and AC impedance method. Alkaline direct methanol fuel cells (ADMFC) comprised Q-PVA/PECH anion-exchange composite polymer membranes were assembled and examined. Experimental results indicate that an alkaline DMFC employing an inexpensive non-perfluorinated Q-PVA/PECH composite polymer membrane shows excellent electrochemical performances. The peak power densities of the DMFC using 4 M KOH + 1 M CH₃OH, 2 M CH₃OH, and 4 M CH₃OH fuels are 17.22, 22.30, and 20.81 mW cm⁻², respectively, under ambient conditions. The Q-PVA/PECH composite polymer membrane appears as a viable candidate for use in an ADMFC.     

Dielectric and EMW absorbing properties of PDCs-SiBCN annealed at different temperatures

Polymer derived SiBCN ceramics (PDCs-SiBCN) were prepared from polyborosilazane and then annealed at 1200–1800 °C in N₂. Effects of annealing temperature on the microstructure, phase composition, dielectric and wave-absorbing properties of ceramics were investigated. Results showed that nano-sized SiC grains were formed in amorphous SiBCN after annealing and the content and crystallization degree of SiC gradually intensified with annealing temperature increasing. The permittivity, dielectric loss and electrical conductivity of PDCs-SiBCN gradually increased as the temperature rose due to the formation of conductivity network of SiC grains and the increase of nano-grain boundary. The increased content of SiC (as the dipole) and interface between SiC nano-grains and amorphous SiBCN phase led to a higher polarization ability and higher dielectric loss. The RC gradually decreased with the annealing temperature increasing, demonstrating the annealed ceramics had the superior wave-absorbing ability and high annealing temperature was conducive to the improvement of wave-absorbing property.     

Dielectric properties of Permalloy granular composite materials

Dielectric and electrical properties of Permalloy granular composite materials have been studied considering the application to left-handed meta-materials. Surface oxidized Permalloy particles have high surface electrical resistance; the eddy current effect in the composite structure is suppressed. The electrical conductivity of compacted Permalloy particles increases with increasing temperature and indicates the semiconductive layer formation on the particle. The low frequency ac electrical conductivity of Permalloy composite materials shows a drastic increase in the particle content between 50 and 60 vol.%. Electrical permittivity spectra of Permalloy composites show a non-metallic characteristic and the enhancement of permittivity is observed with increase of Permalloy particle content.     

Morphological properties of composite solid polymer electrolytes based on polyethylene oxide

Morphological properties of polymer electrolytes based on blends of polyethylene oxide and a perfluorinated polyphosphazene solvated with LiCF₃SO₃ with and without the addition of dispersed γ-LiAlO₂ are reported. The effect exerted on the morphology of the complex electrolytes by the addition of a plasticizer-like propylene carbonate has also been studied. Results indicate the incorporation of γ-LiAlO₂ leads to changes on the morphology of the complex electrolyte, as verified by X-ray diffraction analysis. The major effect observed by plasticizer addition was a decrease on the crystallinity of the system together with a displacement of the T_g towards lower temperatures. © 1998 John Wiley & Sons, Inc. J. Appl. Polym. Sci. 69: 2435–2440, 1998     

Dielectric properties of amorphous cellulose acetate-butyrate polymer films

The dielectric constant, loss tangent and AC conductivity of solution grown cellulose acetate-butyrate films of 5μm thickness were studied as a function of temperature (300-450 K) in the frequency range 10 Hz-10 MHz. The decrease in dielectric constant was observed with the increase in frequency as well as with temperature. A loss peak was observed in the dielectric loss spectra and was identified as the β-relaxation peak. The frequency-dependent conductivity was also studied. The results were interpreted in terms of electronic conduction via hopping processes.     

Dielectric properties of thin films of Babassu‐based polymer and polyaniline blends

In the present work, we describe the preparation and subsequent characterization of polymeric blends consisting of a monoglyceride (MG) synthesized from the Babassu's oil and the already commonly employed polyaniline (PAni). By following changes in the complex impedance of capacitor‐like devices we observe that the presence of MG in the PAni/MG blends decreases electrical conductivity and that this decrease is a function of the content of MG in the blend, i.e., the blend with 30% of MG shows Z′ about seven times greater than the one with 10% of MG. Fourier transform infrared measurements prove the formation of MG and the presence of secondary amine groups (N? H bonds) in the blends, which allow for the chemical doping of PAni by protonation, further studies are necessary to access the viability of employing this new material as active layer in electronic organic devices. Atomic force microscopy images show the formation of agglomerates due to the presence of MG. In addition, the polymeric mixture acts only as a blend, providing a physical interaction between different components. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46198.     

Dielectric properties and electromagnetic wave absorbing performance of single-source-precursor-derived carbon-rich NbC-SiC-C nanocomposites

For the first time, the present work reports the dielectric properties and electromagnetic wave (EMW) absorbing performance of polymer-derived carbon-rich NbC-SiC-C nanocomposites. In our previous work, NbC-SiC-C nanocomposites with the ultra-high temperature ceramic phase NbC as the main phase were synthesized with the allylhydridopolycarbosilane (AHPCS) and niobium pentachloride (NbCl₅) as starting materials. On this basis, divinyl benzene was chosen as carbon-rich source and introduced into the AHPCS and NbCl₅ to form a single-source-precursor. Finally, carbon-rich NbC-SiC-C nanocomposites were successfully synthesized by polymer-derived ceramic approach. Compared with ceramic samples without Nb and with lower carbon content, the carbon-rich NbC-SiC-C nanocomposites show extremely enhanced EMW absorbing performance with minimum reflection coefficient of −51.1 dB at 6.88 GHz for the thickness of 2.27 mm. As a consequence, the resultant carbon-rich NbC-SiC-C nanocomposite has to be considered as structure&function integrated material with excellent EMW absorption performance, which can be applied in hostile environment.     

Emission properties of composite semiconducting polymer nanoparticles

A series of composite polymer nanoparticles was prepared from poly(N‐vinylcarbazole) (PVK) and poly(2,5‐bistriethoxy‐p‐phenylene vinylene‐alt‐phenylene vinylene) (BTEO–PPV‐alt‐PPV). The nanoparticle sizes were measured to be in the range of 50–80 nm with transmission electron microscopy. The photoluminescence intensity of PVK decreased with the content of BTEO–PPV‐alt‐PPV increasing in the composite polymer nanoparticles because the excited states in PVK were quenched by BTEO–PPV‐alt‐PPV. The emission from BTEO–PPV‐alt‐PPV was enhanced in the composite polymer nanoparticles because of energy transfer from PVK to BTEO–PPV‐alt‐PPV for excitation at the absorption maximum of PVK. The energy‐transfer efficiency was markedly improved in the composite polymer nanoparticles versus the composite polymer films according to emission spectral analyses. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Microwave absorbing properties of a thermally reduced graphene oxide/nitrile butadiene rubber composite

Reduced graphene oxide (RGO) with a layered and porous structure was synthesized by thermal exfoliation of graphite oxide. Synthesized RGO is very light weight and flaky. The formation of RGO was studied using Fourier transform infrared and Raman spectroscopies, X-ray diffraction and scanning electron microscopy. Composites were prepared by dispersing 2%, 4% and 10% by weight of the synthesized RGO into nitrile butadiene rubber (NBR) matrix. Microwave absorption properties of RGO/NBR composites were investigated by measuring their complex permittivity and permeability by using waveguide method. Simulation studies show that 10 wt.% of graphene oxide in NBR matrix exhibits high values of reflection loss (>10 dB) over a wide frequency range 7.5–12 GHz and maximum loss is 57 dB at 9.6 GHz at a thickness of 3 mm.     

Effect on properties of PVDF-HFP based composite polymer electrolyte doped with nano-SiO2

Various kinds of nano-SiO₂ using different catalysts were obtained and characterized by scanning electron microscope (SEM) technique. The results showed that the nano-SiO₂ using NH₃·H₂O as catalyst presented the best morphology. Poly(vinylidenefluoride-co-hexafluoropropylene) (PVDF-HFP) based composite polymer electrolyte (CPE) membranes doped with different contents of nano-SiO₂ were prepared by phase inversion method. The as-prepared CPE membranes were immersed into 1.0 M LiPF₆-EC/DMC/EMC electrolytes for 0.5 h to be activated. The physicochemical and electrochemical properties of the CPEs were characterized by SEM, X-ray diffraction (XRD), electrochemical impedance spectroscopy (EIS), and linear sweep voltammetry (LSV) techniques. The results indicate that the CPEs doped with 10 % nano-SiO₂ exhibit the best performance. SEM micrographs showed that the CPE membranes have uniform surface with abundant interconnected micro-pores, and the uptake ratio was up to 104.4 wt%. EIS and LSV analysis also showed that the ionic conductivity at room temperature and electrochemical stability window of the modified membrane can reach 3.372 mS cm^?1 and 4.7 V, respectively. The interfacial resistance R _i was 670 Ω cm^?2 in the first day, then increased to a stable value of about 850 Ω cm^?2 in 10 days storage at room temperature. The Li/As-fabricated CPEs/LiCoO₂ cell also showed good charge–discharge performance, which suggested that the prepared CPE membranes can be used as potential electrolytes for lithium ion batteries.     

耐温抗盐缔合聚合物的制备及性能评价

在丙烯酰胺、丙烯酸的基础上引入抗盐、耐温性能的N-芳基丙烯酰胺(N-AAM)和增粘、增溶性能的甲基丙烯酰氧乙基二甲基烷基溴化铵(MADA),从而实现聚合物耐高温高盐性能与其溶解性、增粘性的有机统一,其结构经红外光谱(FTIR)表征证实。评价了耐温抗盐聚合物(ATSP)的增粘、耐温、高温高盐长期稳定性、驱油等性能,并通过ESEM得到了其在高矿化度下的微观形貌。结果表明,耐温抗盐聚合物增粘、耐温性能优良,在高温高盐条件下稳定性好,聚合物驱及后续水驱的采收率为9.9%。     

Ion-conductive properties of mesoporous silica-filled composite polymer electrolytes

We have synthesized mesoporous silica (MPSi) as a novel type of inorganic filler for polyether-based electrolytes and have characterized the effect of addition on ionic conduction. Both poly(ethylene oxide) (PEO) and PMEO composites filled with MPSi showed higher ionic conductivity than the original and the composites filled with particle silica (pSiO₂). It was considered that the increase is caused by the difference in the surface area between MPSi and pSiO₂. In the PEO composites, the addition of MPSi gave rise to the reduction of crystal PEO and crystalline complex domains. The glass transition temperature of the PMEO composites increased with the addition of the MPSi, in spite that the conductivity increased with increasing the filler contents. It has been suggested that the Lewis acid-base interactions between ions, ether chains and filler surface strongly affect on the ionic conduction in the composite electrolytes.     

超支化复合聚合物的制备及其性能研究

为了研究超支化复合聚合物溶液流变性能,扩大其在驱油领域的应用,通过阳离子超支化聚酰胺胺(HMC)与四元共聚物P(AA/AM/AMPS/MMA)制备了复配体系溶液(PA-MC)。结果表明,当聚合物浓度为2 000 mg/L时,HMC最佳加量为30 mg/L,PA-MC表观黏度为560.3 mPa·s;在120℃、7.34 s^(-1)下,PA-MC表观黏度为165.6 mPa·s;在70℃下老化60 d后,黏度为274.2 mPa·s,黏度保留率为54.1%,且其微观形貌没有明显变化;在10 000 mg/L NaCl、1 500 mg/L MgCl_2和1 500 mg/L CaCl_2中,PA-MC表观黏度分别为26.4,24.5,26.3 mPa·s,优于HPAM的16.5,14.5,16.3 mPa·s。另外,岩心驱替实验表明PA-MC具有较好的驱油性能,可以用作提高采收率的聚合物驱油剂。     

Electrochemical synthesis,characterization and capacitive properties of novel thiophene based conjugated polymer

In this paper, a novel thiophene based monomer, 1-(pyren-1-yl)-2,5-di(thiophen-2-yl)-1H-pyrrole, PThP, was synthesized and characterized by ¹H NMR and ¹³C NMR spectroscopic methods. The electrochemical behavior and electropolymerization of this novel monomer were performed on pencil graphite electrode (PGE) by cyclic voltammetry. The effect of solvent, dopant, scan number and scan rate on the electropolymerization and properties of the conjugated polymer films were investigated. The capacitive properties of the poly(PThP) films were tested by electrochemical impedance spectroscopy (EIS). The highest specific capacitance value was calculated for the conjugated polymer modified PGE that was obtained in 0.1 M tetrabutylammonium perchlorate/dichloromethane solution for 30 cycles at 25 mV/s scan rate as 25.45 mF cm⁻². The surface morphologies of the conjugated polymer modified electrodes were determined by scanning electron microscopy (SEM).     

Transient elongational properties of an in situ generated polymer/polymer composite

The elaboration of a n in‐situ composite consisting of ethylene vinyl acetate copolymer (EVA) and polybutylenetherephtalate (P m was investigated. An inter‐chain chemical reaction during processing operations was used to generate a grafted PBT‐g‐EVA copolymer at the interface of the two polymers. Composites with either nodular or fibrillar morphologies were obtained. Fibrillar morphology was achieved by stretching the extruded blend at the exit of the die. Elongational properties of such composites were investigated by using the fiber wind‐up technique. The influence of the aspect ratio of PBT solid inclusions on the elongational viscosity was discussed for a series of EVA/PBT composites. Clearly, the strain hardening softening properties were found to be strongly affected by the aspect ratio. Increasing the aspect ratio of PBT solid particles made the strain hardening weaker and even gave strain‐softening. This behavior is emphasized by the presence of the grafted PBT‐g‐EVA copolymer. The results suggest that strain‐hardening or softening of such composites is correlated to the homogeneity of the flow at EVA‐PBT interface: the elongational flow is disrupted in the interphase region so that the deformation around the particle is not homogeneous.     

Preparation and characterization of a novel antibacterial acrylate polymer composite modified with capsaicin

A novel antibacterial acrylate polymer composite modified with capsaicin was successfully synthesized by a two-step reaction. Capsaicin and acryloyl chloride were firstly esterified, and then applied to solution polymerization with acrylate monomers and styrene. The yield of the esterified products was about 85.3%. The polymer was characterized by Fourier transform infrared spectroscopy (FTIR), gel permeation chromatography (GPC), thermogravimetric analysis (TGA), contact angle (CA) and antibacterial ring tests. The number-average molecular weight (M_n) of the polymer was 27214, based on the capsaicin-acrylate dosage of 6.5 wt%. The TGA revealed a stable thermal property. The contact angles of the polymers films on tinplate increased from 77.5° to 86.2° with the increasing amount of capsaicin-acrylate. The antibacterial tests demonstrated excellent antimicrobial capability of the polymers.     

Dielectric properties and morphology of polymer composites filled with dispersed iron

The dielectric properties and the structure of various metal–polymer composites, based on a polymer matrix of polyamide (PA), polyethylene (PE), polyoxymethylene (POM), or blend PE/POM filled with dispersed iron (Fe) particles, have been investigated in this work. In PE–Fe, PA–Fe, and POM–Fe composites the filler spatial distribution is random. In the PE/POM–Fe composites, the polymer matrix is two‐phase and the filler particles are localized only in the POM phase, resulting in an ordered distribution of the dispersed filler particles within the blend. The concentration and frequency dependence of the dielectric permittivity, ε′, and the dielectric loss tangent, tanδ, are described in terms of the percolation theory. The experimental values of the critical exponents (namely, s, r, and y) are in good agreement with those predicted by the theory for the composites with random filler distribution. The PE/POM–Fe composites demonstrate low value of the percolation threshold, P_C, and high values of the critical exponents r and y. This is attributed to the specific structure of these composites. A schematic model for the morphology of the composites studied has been proposed. This model explains the peculiar behavior of the PE/POM–Fe composites by assuming ordered distribution of the filler particles in a binary polymer matrix. The proposed model is in good agreement with the results of optical microscopy. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 3013–3020, 2003     

高吸油树脂的合成及对硝基苯的吸附

采用悬浮聚合法合成了丙烯酸系高吸油性树脂。考察了树脂对硝基苯以及对模拟消防废水中硝基苯的吸附性能。研究了吸附树脂量、硝基苯初始浓度、吸附温度、离子浓度、pH等因素对均相含硝基苯的消防水吸附的影响。结果表明:吸附5 h后,对纯硝基苯的最大吸油率为30.5 g/g,吸附10 min后,对硝基苯吸油率达饱和吸油率的50%。当树脂用量为25 g/L时,硝基苯去除率达70%。树脂还具有良好的耐热及耐酸碱性,且离子浓度对吸附率无显著影响,因而能用于多种环境体系。