Dielectric Response of Commercial Polycarbonate

Contour maps of complex relative permittivity within the range - 175°C to 195°C and 0.1 Hz to 3 MHz are presented for basic and ultraviolet resistant grades of a commercial poly(dian carbonate). Several dispersion regions common to both materials are identified, together with an additional region at high temperatures in the ultraviolet resistant material. Comparisons are made with earlier investigations, and possible sources are suggested for each dispersion.     

多壁碳纳米管复合聚碳酸酯/苯乙烯系聚合物复合材料导电性能的研究

采用一步法将聚苯乙烯（PS）、苯乙烯-丙烯腈共聚物（SAN）和甲基丙烯酸甲酯-苯乙烯共聚物（MS）分别与聚碳酸酯（PC）、多壁碳纳米管（MWCNTs）熔融混合,得到PC/PS/MWCNTs、PC/SAN/MWCNTs和PC/MS/MWCNTs三种复合材料。透射电子显微镜和场发射扫描电子显微镜观察表明,MWCNTs选择性分散在PC相中,这与Sumita模型预测的结果完全吻合,且随着PS、SAN或MS含量的增加,体系的体积电阻率-苯乙烯系聚合物含量曲线能够很好地拟合到PC/MWCNTs体系的体积电阻率-MWCNTs有效体积浓度曲线上,体系的体积电阻率变化符合有效浓度的概念。     

聚合物熔体的介电性能研究

研究了聚碳酸酯（PC）、低密度聚乙烯（LDPE）两种聚合物熔体的介电性能。结果表明, PC熔体在220~320 ℃范围内,PE-LD熔体在120~300 ℃温度范围内,两种聚合物熔体的介电常数在低频时随频率的增加而显著减小;频率为10 Hz时,PC熔体的介电常数在220~320 ℃范围内随温度的升高而增大,介电常数变化较大,而频率为100~1 000 Hz时,PC熔体的介电常数在此温度范围内随温度的升高变化较小;频率为10 Hz时,PE-LD熔体的介电常数在120~300 ℃范围内随温度的升高表现出先增大后减小,再增大的复杂关系,频率为1 000 Hz时,PE-LD熔体的介电常数受温度的影响较小。     

Simultaneously Improved Thermal Conductivity and Dielectric Properties of NBR Composites by Constructing 3D Hybrid Filler Networks

This work aims to address the heat accumulation issue in electronic components during high-frequency operation through the preparation of novel thermally conductive composites. First, polydopamine (PDA) and in-situ growth of silver (Ag) nanoparticles are applied for the surface modification of graphene oxide (GO) and carbon nanotube (CNT) to prepare pGO@Ag and pCNT@Ag hybrid filler, respectively. Then, nitrile butadiene rubber (NBR) is chosen as the polymeric matrix and simultaneously incorporated with both pGO@Ag and pCNT@Ag to prepare polymeric composites with excellent thermal conductivity (TC) and dielectric constant (ɛ_r). Due to the construction of 3D heat conduction networks by utilizing 2D pGO@Ag and 1D pCNT@Ag, the fabricated NBR composites achieved the maximum TC of 1.0112 W/(mK), which is 636% higher than that of neat NBR (0.1373 W (mK)⁻¹). At the filler loading of 9 vol%, the TC of pGO@Ag/pCNT@Ag/NBR composite is 152% that of GO/CNT/NBR composite (0.6660 W (mK)⁻¹). Moreover, due to electron polarization effect of GO and CNT and micro-capacitor effect of Ag nanoparticles, a large ɛ_r of 147.12 is attained at 10 Hz for NBR composites. Overall, the development of dielectric polymer materials with high TC is beneficial for enhancing the service life and safety stability of the electronic components.     

Electric and Dielectric Properties of Some Fluorescent Dye/PMMA Solar Concentrators

The effect of dye concentrations of perylene, RH-6G and K₁ doped in polymethylmethacrylate (PMMA) as matrix material, on the electrical properties of some fluorescent solar concentrator (FSC) have been investigated. The samples were prepared by dissolving grains of both PMMA and dyes in chloroform, which were then left at room temperature to evaporate the solvent. The samples were characterized by differential scanning calorimeter (DSC). The results of both dc conductivity (σ_dc) and ac conductivity (σ_ac) showed that the total conductivity σ_tot(w) is higher than σ_dc and the activation energy of σ_tot is lower than that of (σ_dc) due to the increase of the applied field frequency, which enhances the carrier jumping and subsequently the conductivity value. The dielectric properties (dielectric constant (?′), dielectric loss (?″), and dielectric tangent (tanδ) have been studied. They show that ?′ increases by increasing the concentration of the dyes doped in PMMA. All the dielectric constants, the dielectric loss and loss tangent temperature dependence, show a peak value affected by the dye concentration as well the frequency changes. The temperature dependence of the exponent S shows that at low temperature the conduction obeys a quantum mechanical tunnel model, while at high temperature the conduction obeys the correlated barrier-hopping model.     

聚碳酸酯微孔泡沫塑料及其基体材料的拉伸力学性能

针对几种不同密度的微孔碳酸酯泡沫塑料进行了拉伸实验，得到了其应力－应变曲线和主要的力学性能参数，同时，还对实体聚碳酸酯塑料和经气体过饱和处理的聚碳酸酯塑料进行了拉伸实验，得到了基体材料的力学性能参数，并讨论了气体过饱和处理对其体材料力学性能的影响。     

聚碳酸酯型聚氨酯—环氧树脂IPN的性能及结构形态

由甲苯二异氰酸酯和聚六亚甲基碳酸酯二醇制备聚氨酯预聚体,再由该预聚体、双酚A环氧树脂等用同步法合成了聚碳酸酯型聚氨酯-环氧树脂互穿网络聚合物（PCPU－EPIPN）。红外光谱分析表明PCPU和EP两组分间存在一定的化学结合。差示扫描量热分析及热重分析研究表明：IPN在高温区存在单一玻璃化转变峰,当PCPU与EP的质量比mU／mE＝25／75时,IPN的Tg最高且热稳定性最好。透射电镜和扫描隧道显微镜研究表明,PCPU与EP的配比对IPN的形态结构有显著的影响。应力-应变测试发现：当mU／mE＝25／75时IPN体系力学性能最佳。     

酒石酸改性BT增强PP复合材料导热与介电性能

以酒石酸为改性剂,对钛酸钡(BT)颗粒进行表面改性,制备了聚丙烯(PP)/纳米氧化铝(Al2O3)/改性BT系列3相复合材料.通过傅里叶红外光谱、扫描电子显微镜、介电频谱仪、导热分析仪对复合材料的红外光谱、微观形貌、介电性能、导热性能等进行分析表征.结果表明,酒石酸对BT颗粒的表面改性能有效改善BT、Al2O3等无机填...     

改性聚碳酸酯板材的制备及性能研究

采用由丙烯酸类树脂、有机溶剂和紫外线吸收剂(UVA)组成的抗紫外线透明涂层制备改性聚碳酸酯(PC)板材,通过透光率/雾度测定仪、加速老化测试仪、分光光度计研究了涂层对PC板材光学和力学性能的影响。结果表明,抗紫外线涂层与PC板表面具有极佳的附着力,这种涂层具有优异的抗紫外线性能,未涂覆涂层的PC板经紫外光老化120h后黄色指数达到11左右,而涂覆该涂层的PC板的黄色指数仅为1左右,同时该板材能有85%以上的可见光透过率,120h紫外光加速老化后,板材的可见光透过率和力学性能基本保持不变。     

Properties of Recycled Polycarbonate/Waste Silk and Cotton Fiber Polymer Composites

Polymer-based composite structures have advantages over many other materials. The most important advantage is the higher mechanical properties obtained from the composites when supported by fiber reinforcement. The mechanical and thermal properties of fiber-reinforced composite structures are affected by the amount of fibers in the structures, orientation of the fibers and fiber length. Silk and cotton fibers are used in many fields but especially in clothing and textiles. However, there is not enough research on their usage as reinforcement fibers in composite structures. Silk fibers as a textile material have better physical and mechanical properties than other animal fibers. The improvement of the mechanical and physical properties of the composite structures allows them to be used in many areas. From economical, technological and environmental points of view, the improvement of mechanical and physical properties of polymeric materials are receiving much attention in recent studies.

In this study, different application areas were chosen to evaluate the waste silk and waste cotton rather than classic textile applications. Waste silk and cotton and recycled polycarbonate polymer were mixed and as a result composite structures were obtained. Silk and cotton waste fiber dimensions were in between 1 mm, 2.5 mm and 5 mm. The recycled PC/silk and cotton wastes were mixed in the rates of 97%/3%. Mixtures were prepared by twin-screw extruder. Tensile strength, % elongation, yield strength, elasticity modulus, Izod impact strength, melt flow index (MFI), heat deflection temperature (HDT) and Vicat softening temperature properties were determined. To determine the materials' thermal transition and microstructure properties, differential scanning calorimetry (DSC) and scanning electron microscopy (SEM) were used.     

Morphology and Mechanical Properties in Polymer Blends of Photocurable Polymer and Polycarbonate

Relationships between the morphologies and mechanical properties of binary blends of a photocurable polymer (2‐propenoic acid, (octahydro‐4,7‐methano‐1H‐indenediyl) bis(methylene)ester; DCA) and a linear polymer (poly(4,4′‐cyclohexylidene bisphenol carbonate); PCz) have been investigated. The blend films are prepared by in situ photopolymerization of homogeneous mixtures of a DCA‐monomer and PCz. The phase structure has been converted from a semi‐interpenetrating polymer networks (semi‐IPN) structure to a bicontinuous structure by controlling the cure temperature. Bicontinuous phase‐separated structures can be obtained by curing a wide range of compositions of 17–50 wt.‐% PCz at high temperatures. Miscible semi‐IPN structures are attained by means of photopolymerization below the glass transition temperature of the homogenous mixture before performing photoirradiation, such that magnetic relaxation measurements showed the blend to be miscible in the 10 nm order. The tensile strength and modulus reached a maximum in those blends having an intermediate vague phase structure between semi‐IPN and bicontinuous structures that have a strong interfacial interaction, which leads to incomplete phase decomposition in the PCz‐rich matrix phase. The maximum strength and modulus prepared under optimum condition are inferior to those of the individual components. In contrast, the elongation and break energy are greatly improved in those blends with bicontinuous structures having a diffused phase boundary.

DCA‐rich domain size in bicontinuous structure for DCA/PCz system, as a function of cure temperature; (□) 17 wt.‐% PCz, (○) 30 wt.‐% PCz, and (?) 50 wt.‐% PCz.     

脂肪族聚碳酸酯型聚氨酯软泡性能的影响因素

以自制的脂肪族聚碳酸亚乙酯二元醇和液化MDI为主要原料,制备了聚碳酸酯型聚氨酯软泡,并对发泡剂、异氰酸酯、稳定剂用量及操作工艺等对泡沫体性能的影响进行了讨论。结果表明,通过调节发泡剂、异氰酸酯、稳定剂用量等,可以得到密度在8~80kg/m3之间、压缩强度在10~108kPa之间的聚氨酯软泡。     

Dielectric and Mechanical Behavior of Treated Paper Sheet

Abstract

The dielectric properties of different polymers, polymethyl methacrylate. polystyrene, mixture of them (1:1) and polyvinyl alcohol films were studied. Also, the dielectric and mechanical properties were measured to study the intermolecular interactions of paper sheet impregnated in the different polymers under investigation. The retained polymer on dipped paper sheet is lowest in case of mixed polymer solutions than that of each polymer solution alone. The retained polymer on paper sheet from aqueous polymer solution is lower than that dipped in organic solvent polymer solutions. The mixture of 1:1 PS and PMMA has a higher permittivity than that of each of both polymer alone. The treatment of paper sheet with polymer solutions improved their dielectric and mechanical properties, whereas the mixture of PS and PMMA is the best one for improving treated paper sheet.     

混杂铝粒子对环氧树脂导热性能与介电性能的影响

选取平均粒径分别为2、18、50 μm的3种铝粒子,两两混合填充环氧树脂形成3种复合材料,铝粒子的总含量为60 %。研究了复合材料中小粒径铝粒子相对含量(Ws)的变化对环氧树脂热导率及介电性能的影响。结果表明,随着Ws的改变,复合材料的热导率、热扩散系数及介电性能均发生变化。2种铝粒子的粒径差异越小,复合材料热导率达到最大值时的Ws值越小。在W50μm/W18μm约为2时,复合材料的介电常数达到最大值;介电损耗受Ws影响不大,仍处于很低值(＜0.02)。     

偶氮聚碳酸酯的制备与性能研究

以对氨基苯甲酸、亚硝酸钠和苯酚为原料,通过重氮偶合反应合成了对羟基偶氮苯甲酸,并用红外光谱和核磁共振对所合成的对羟基偶氮苯甲酸的结构进行了表征。将羟基偶氮苯甲酸与聚碳酸酯进行熔融混合并进行酯交换反应,制备了偶氮聚碳酸酯。通过光学性能和力学性能研究发现,所制备的偶氮聚碳酸酯具有优异的光致变色性能和透明性,力学性能与聚碳酸酯相当。     

Dielectric Relaxation and Electrical Conductivity Study in Thiourea- Doped Poly (Vinyl Alcohol)

Abstract

FT-IR, UV-spectroscopy and X-ray diffraction of thiourea-Poly (vinyl alcohol) (PVA) complexes have been investigated. It was observed that thiourea affected the structure of PVA. X-ray study revealed that as the thiourea salt increases the crystallinity of PVA increases. The dielectric properties of thiourea-PVA complexes were investigated in the frequency range 0.2 to 100 kHz and the temperature range 293 to 433 K. All samples are characterized by high values of dielectric permittivity at low frequencies and high temperatures. The results are discussed in terms of interfacial Maxwell-Wagner-Sillars (MWS) polarization and space-charge polarization. Different relaxation modes, i.e., β and α-relaxations have been observed in pure PVA. AC conductivity measurements of samples showed that the hopping conduction mechanism dominates at low temperature region, from room temperature to the glass transition temperature.     

Dielectric Study of Tetraalkylammonium and Tetraalkylphosphonium Levulinate Ionic Liquids

Broadband dielectric spectroscopy in a broad temperature range was employed to study ionic conductivity and dynamics in tetraalkylammonium- and tetraalkylphosphonium-based ionic liquids (ILs) having levulinate as a common anion. Combining data for ionic conductivity with data obtained for viscosity in a Walden plot, we show that ionic conductivity is controlled by viscosity while a strong association of ions takes place. Higher values for ionic conductivities in a broad temperature range were found for the tetraalkylphosphonium-based IL compared to its ammonium homolog in accordance with its lower viscosity. Levulinate used in the present study as anion was found to interact and associate stronger with the cations forming ion-pairs or other complexes compared to the NTf₂ anion studied in literature. In order to analyze dielectric data, different fitting approaches were employed. The original random barrier model cannot well describe the conductivity especially at the higher frequencies region. In electric modulus representation, two overlapping mechanisms contribute to the broad low frequencies peak. The slower process is related to the conduction mechanism and the faster to the main polarization process of the complex dielectric permittivity representation. The correlation of the characteristic time scales of the previous relaxation processes was discussed in terms of ionic interactions.     

Structure and Dielectric Properties of Lead Pyrochlores

This work investigates the structure and stability of the pyrochlore solid solution Pb _n Nb₂O_{5+ n} using a combination of high-resolution electron microscopy and electron diffraction. The microwave dielectric properties of the series 1.5 ≤ n ≤3.0 have been established, and the effect of the substitution of Ta⁵⁺ for Nb⁵⁺ on dielectric properties has also been investigated for n = 1.5 and 2.0. Single-phase cubic pyrochlore was obtained for n = 1.5. Compositions for which n > 1.5 showed discreet PbO-rich layers on {111}_cubic planes between alternating slabs of pyrochlore, similar in appearance to Ruddlesden–Popper phases. The occurrence of these layers results in a lowering of the overall symmetry to trigonal, and their presence was found to have a profound effect on the microwave dielectric properties.     

Dielectric and Electromechanical Properties of Textured Niobium-Doped Bismuth Titanate Ceramics

Textured Nb-doped bismuth titanate ceramics (Bi₄Ti_{3− x /5}- Nb _{x /5}O₁₂, where x = 0.02) were fabricated by templated grain growth. It was found that the use of a fine precursor powder led to enhanced densification of the ceramic, while Nb doping reduced electrical conduction and dielectric loss, which enabled poling at high temperatures and high electric fields. Sintered tapes showed anisotropic dielectric and piezoelectric properties when measured parallel and perpendicular to the casting plane (e.g., the remanent polarization differed by more than a factor of 15 in the two directions). The piezoelectric constant parallel to the casting plane of the tape was ∼30 pC/N, or ∼77% of the single-crystal value. Thermal depoling studies demonstrated that high-temperature piezoelectric applications are possible up to ∼450°C in textured, doped bismuth titanate.     

聚碳酸酯二元醇及其在聚氨酯材料中的应用

本文论述了聚碳酸酯二元醇及聚碳酸酯型聚氨酯材料的发展概况，并分别简述了聚碳酸酯二元醇的合成方法、应用及聚碳酸酯型聚氨酯材料的性能与特点。