Piezoresistivity of silicone‐rubber/carbon black composites excited by Ac electrical field

Flexible conductive composites were prepared using liquid silicone rubber as a matrix and conductive carbon black (CCB) as a filler, and the filler loading was varied from 1 to 15 phr in mass ratio. The surface conductivity was studied as a function of CCB concentration (1, 5, 10, 15 wt %), frequency in the range from DC to 1 MHz. The AC resistivity of the composites with low CCB concentration was found to be frequency dependent, whereas the composites with high CCB concentration was almost frequency independent. The resistance/impedance drift of the composites with time decreases sharply with the increase of frequency of applied electrical field. The piezoresistivity of the composite with 5 wt % CCB concentration (the upper percolation limit) was studied. It is found that the composite exhibits prominent positive piezoresistivity coefficient effect through the measurement frequency, and the sensitivity becomes steeper with the increase of exciting frequency. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Effect of Solvent on Segregated Network Morphology in Elastomer Composites for Tunable Piezoresistivity

Flexible, light‐weight, and wearable electronics have significant potential for the development of Internet of Things. Flexible sensors with tunable piezoresistive properties are in high demand for various practical applications. Herein, different morphology thermoplastic polyurethane (TPU)/ carbon nanostructure (CNS) composites with segregated network are obtained by swelling the TPU powders using various solvents. The better solvent for TPU, dimethylformamide (DMF), renders the composites with 0.7 wt% CNS stronger polymer‐filler interactions, resulting in significantly improved piezoresistive sensitivity at strain larger than 150%. Also the gauge factors (G_Fs) for these composites are 9.7 in the range 0–60% strain and 19.3 for 60–100% strain. In contrast, the composites with ethanol (EtOH) and tetrahydrofuran (THF) which swell less the TPU show delayed increase in piezoresistivity and G_Fs of 2.2 and 3.5 for strain up to 100%, respectively, suggesting potential applications for stretchable conductors.     

Piezoresistivity in Semiconducting Positive Temperature Coefficient Ceramics

The experimental and theoretical aspects of piezoresistivity in semiconducting, positive temperature coefficient (PTC) of resistivity ceramics will be reviewed. Emphasis will be placed on their potential application in sensor technology. Future material and modeling challenges are highlighted.     

氧化铁/层状双金属氢氧化物复合材料的制备

制备由不同结构单元组成的复合材料是提高材料性能的一种有效方法.分别采用两种方式(双滴共沉淀法和LDHs层板附着生长法)制备Fe3 O4/层状双金属氢氧化物(LDHs)复合材料.利用X-射线衍射、电子显微分析和红外光谱等测试方法研究了LDHs和Fe3 O4的复合方式对复合材料形貌、粒径和结晶性能的影响.同时对比分析了两种制备方案得到的Fe3OJLDHs复合材料生长规律.实验结果表明,采用双滴共沉淀法制备的Fe3OJLDHs复合材料具有层状结构和良好的结晶性.     

硫酸盐-冻融循环下自感应水泥砂浆的耐久及压敏性能

为提升寒冷地区建筑结构的实时损伤监测效果,研究了硫酸盐-冻融循环作用下采用短切碳纤维与铁尾矿作为导电材料制备的自感应水泥砂浆的耐久与压敏性能。利用质量损失、相对动弹性模量及抗压强度损失为依据探讨耐久性能变化规律,以电阻率变化率-压应力的相关关系反映硫酸盐-冻融循环作用下压敏性能发展规律并解释其导电机理,并采用平均应力敏感系数评价硫酸盐-冻融循环作用下压敏性能稳定性。结果表明,碳纤维体积掺量为0.4%、铁尾矿替代率为30%(质量分数)组合掺入水泥砂浆时,其耐久性能与压敏性能均达到较高水平,但硫酸盐-冻融循环造成的孔洞与裂缝会导致铁尾矿碳纤维水泥砂浆电阻率变化率-压应力呈一阶指数衰减关系,可采用Plane模型来反映平均应力敏感系数衰减程度与冻融循环次数、铁尾矿替代率之间良好的相关关系。     

纳米碳黑水泥基复合材料压阻效应的若干特性研究

对纳米碳黑水泥基复合材料烘干减少内部的含水量,测定材料失水前后相应的压阻效应,研究含水量变化对材料压阻效应特性影响,试验结果表明:纳米碳黑水泥基复合材料的压阻效应具有正、负两种表现形式,材料在含水量较高或者烘干至恒重状态时为正压阻效应,而在一定含水量状态时则表现为负压阻效应;纳米碳黑水泥基复合材料加载和卸载对应的△R/R0-stress曲线不重合,材料的电阻变化率△R/R0在荷载作用下具有不可逆性,压阻效应呈现非线性特征;材料在不同应力状态下,压阻灵敏度不同,压阻灵敏度随着应力水平增大而降低,在较大的应力状态下材料的压阻出现了"迟钝"现象.     

氧化石墨烯与纳米氧化铁复合物的制备及性能研究

文章用Hummers法制备氧化石墨,以绿矾为原料、采用氯酸钠氧化制备纳米氧化铁,采用超声共混,搅拌,烘干制的复合物,通过FT-IR/TG/TEM等进行表征,结果表明,氧化石墨完全剥落,氧化铁在内分散很好,两者界面相容很好。复合材料吸附性好,有很好吸附砷的功能。     

Lead Zirconate Titanate Fiber/Polymer Composites Prepared by a Replication Process

The woven replication process was used to fabricate lead zirconate titanate (PZT)/polymer composites with 1–3, 2–3, and 3–3 connectivities by starting with novoloid-derived carbon fiber, woven fabric, and nonwoven felt templates, respectively. Activated carbon-fiber template material was impregnated with PZT by soaking it in a solution containing stoichiometric amounts of dissolved lead, zirconium, titanium, and niobium ions. Heat treatment burned out the carbon, leaving a PZT replica with the same form as the template material. Replicas were sintered in a controlled atmosphere and backfilled with an epoxy polymer to form final composites. This method, which is believed to be adaptable for mass production, is capable of producing composites with extremely fine microstructures. Woven composite samples have fiber tow diameters of 200 to 250 μm and spacings between tows of about 150 to 250 μm. Average d ₃₃= 90 pC/N, g ₃₃= 211 mV · m/N, and d_hg_h hydrophone figure of merit of 2100 × 10⁻¹⁵ m²/N values are reported for woven PZT/polymer composites.     

Influence of Reactice Processing on the Properties of PP/Glass Fiber Composites Compatibilized with Silane

Summary: Composites of PP reinforced with 20 wt.‐% of short glass fibers were prepared by extrusion using VTES as a coupling agent. The addition of VTES was performed via in‐situ functionalization of PP and by a two‐step process in which PP was functionalized before the composite preparation. The obtained samples were characterized using rheometry, mechanical tests and microscopy. Both processes allowed the fiber/matrix interaction to increase. It was found that the VTES content affected the viscosity of the system by means of three different mechanisms: reduction of β‐scission reactions, decrease of fiber sliding and plasticizing effect on the matrix. Whereas the first two mechanisms increased the viscosity of the final composite after unreacted VTES removal, the third one reduced the viscosity during the process and contributed to fiber‐length preservation. The effects of VTES and peroxide contents on the Young's modulus were closely related to their effects on the final fiber length, indicating the effectiveness of using VTES as a coupling agent. Comparison between in‐situ functionalization and the two‐step process with prefunctionalization showed that in‐situ functionalization led to a lower degree of chain breakage, even when it was performed in the presence of peroxide.

Scanning electron micrographs of PP/glass fiber composite prepared without coupling agent.     

碳纤维水泥基复合材料压敏性的灵敏度及机理分析

采用阶梯循环加卸载方式,对碳纤维水泥基复合材料在不同应力下压敏性的变化进行试验,提出压敏性的灵敏度概念,对比了未经烘干与经烘干后两种情况下压敏性的灵敏度差异,试验结果表明:未经烘干的碳纤维水泥基复合材料呈现正压敏特性,而烘干后的材料呈现负压敏特性,但两者压敏性的灵敏度均随受压应力的增加而减小,并且经烘干后,材料压敏性的灵敏度随受压应力增加而衰减的速度比未经烘干材料的衰减速度慢.应用隧穿效应和电容效应共同作用机理能较好的分析试验现象.     

SnO2–polyaniline composites for the desensitization of Al/SnO2 thermite composites

Nanothermites consisting of a reducing metal and a metal oxide nanopowder represent a new generation of energetic materials in pyrotechnics due to their impressive reactive properties. However, their extreme sensitivity regarding electrostatic discharge appears to be detrimental to their future practical applications. Herein, the mitigation of the sensitivity thresholds of the aluminium/tin (IV) oxide energetic nanocomposite is successfully achieved by using a conducting polymer, polyaniline (PAni). PAni was introduced within the thermite by the chemical polymerization of an oxidizer/PAni hybrid matrix. The SnO₂–PAni composites were characterized by X-ray diffraction, Fourier transform infrared spectroscopy, thermogravimetric analysis, electrical conductivity measurements, and transmission electron microscopy. The derived Al/SnO₂–PAni thermites were investigated in terms of sensitivities and reactivity. Results revealed gradual desensitization of the Al/SnO₂ thermite as a function of the concentration of PAni for both the electrostatic discharge (0.14–1212 mJ) and friction (216–360 N) tests while maintaining reactive energetic composites. This work presents a way for the preparation of insensitive and reactive energetic formulations. © 2020 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020 , 137, 48947.     

Preparation of Polymethylmethacrylate-Reinforced Functionally Graded Hydroxyapatite Composites

A functionally graded hybridization approach has been used in the formation of polymer-ceramic composites of polymethylmethacrylate (PMMA) and hydroxyapatite (HAp). HAp was successfully reinforced by sedimentary HAp distributions on a PMMA matrix using a centrifuge to avoid stress convergence on the interface. The stress-strain curves of the functionally graded PMMA-HAp composite showed sufficient mechanical strength with reduced brittleness. Scanning electron micrographs also showed evidence of exposed HAp on the surface of the composites.     

接枝炭黑/聚乙烯导电复合材料正电阻温度系数(PTC)效应研究

用接枝炭黑作导电粒子研究了在聚乙烯基材中的正 (电阻 )温度系数 (PTC)效应。结果发现 ,甲基丙烯酸甲酯接枝的炭黑在高密度聚乙烯中能表现出较好的 PTC效应。从实验现象分析 ,接枝炭黑的 PTC效应是结晶熔融和体积膨胀双重变化共同作用的结果。     

Thermal Conductivity of Platelet-Filled Polymer Composites

Platelet-shaped particles of similar size and shape were investigated as fillers for improving the thermal conductivity of polymer–ceramic composite materials. The conductivities of composites filled with hard, stiff ceramic particles exceeded 3.5 W·(m·K)⁻¹, or >20 times the conductivity of the polymer matrix, and were shown to be almost independent of the intrinsic filler conductivity range of 33–300 W·(m·K)⁻¹. In contrast, the thermal conductivity of composites filled with soft, platelet-shaped BN fillers reached over 13 W·(m·K)⁻¹. A mechanism is proposed whereby deformation of the soft filler particles provides improved particle-to-particle connectivity and allows greater packing density, resulting in the ability to achieve much higher conductivity than is possible for hard and stiff particles of similar initial morphology. Experimental results are discussed in light of various thermal conductivity prediction models in the literature.     

The Functional and Application Possibilities of Starch/Chitosan Polymer Composites Modified by Graphene Oxide

This study describes functional properties of bionanocomposites consisting of starch/chitosan/graphene oxide (GO) obtained using the green synthesis method, such as water-barrier and optical properties, as well as the rate of degradation by enzymatic and acid hydrolysis. The toxicity of the composites and their effects on the development of pathogenic microflora during storage of meat food products was also investigated. Although the results showed that the barrier properties of the composites were weak, they were similar to those of biological systems. The studies carried out confirmed the good optical properties of the composites containing chitosan, which makes it possible to use them as active elements of packaging. The susceptibility of starch and chitosan films to enzymatic and acid hydrolyses indicates their relatively high biodegradability. The lack of toxicity and the high barrier against many microorganisms offer great potential for applications in the food industry.     

Softwood Distillate as a Bio-Based Additive in Wood-Plastic Composites

The possibility of using softwood distillate as a bio-based additive or filler in wood-plastic composites (WPCs) was studied by adding various amounts (1–20 wt%) of distillate to a commercial WPC consisting of thermally treated sawdust in a polypropylene (PP) matrix. Softwood distillate was obtained as a secondary product from industrial ThermoWood® processing and it was further processed in the laboratory. The addition of softwood distillate significantly enhanced the mechanical properties of WPC when the distillate content was 2 wt%; tensile strength increased by 5%, tensile modulus by 3%, flexural strength by 3%, and modulus of elasticity by almost 2% compared with the unmodified WPC. In addition, a considerable decrease (over 16%) in water absorption was observed on distillate addition. Proton-transfer-reaction time-of-flight mass-spectrometry (PTR-TOF-MS) analyses revealed that the addition of softwood distillate increased release rates of volatile organic compounds (VOCs) in general, and that the odor of acetaldehyde and guaiacol is detectable in several WPCs. Overall, softwood distillate had positive effects on this particular WPC.     

New Diluents for Dental Composites

Five new urethane groups containing monomers 1 – 5 , acetylated glycerol dimethacrylate (AGDMA), and glycerol trimethacrylate (GTMA) are synthesized as alternative diluents to triethylene glycol dimethacrylate (TEGDMA) for dental resins or composites. The synthesized monomers are characterized by means of ¹H NMR, ¹³C NMR, and IR spectroscopy. The secondary acrylamide group containing hybrid monomers 1 and 2 are solids. However, the monomers 3 – 5 , AGDMA and GTMA are colorless and relatively low‐viscosity liquids. They are not mutagenic in the Ames test and show a lower cytotoxicity and a lower polymerization shrinkage compared to TEGDMA. The tertiary amide group containing crosslinker 3 shows a significantly higher photopolymerization rate compared to that of TEGDMA in the presence of the monomolecular Ge‐based photoinitiator Ivocerin. The synthesized diluents are evaluated in experimental dental formulations for resins, cements, and direct filling composites using a conventional binary camphorquinone/amine photoinitiator.

     

炭黑填充复合型导电聚合物的研究进展

在聚合物基体中添加导电炭黑以降低聚合物的电阻率,是目前最为常用的制备导电聚合物的方法。综述了炭黑填充复合型导电聚合物的研究进展。对影响复合材料导电性能及渗滤阈值的因素进行了讨论。重点介绍了使用共混聚合物作基体,并利用炭黑在共混基体中的非均相分布来降低炭黑用量的研究。     

Electrohydrodynamic Direct Writing of Biomedical Polymers and Composites

A recently developed electrohydrodynamic printing method is described that can be used to create ordered structures and complex patterns using coarse processing needles and two polymeric materials. The results highlight the method's potential for direct 3D writing of biomedical polymers and composites for a variety of biomedical applications.

     

Advances in Piezoelectric Polymer Composites for Energy Harvesting Applications: A Systematic Review

Polymeric piezoelectric composites for energy harvesting applications are considered a significant research field which provides the convenience of mechanical flexibility, suitable voltage with sufficient power output, lower manufacturing cost, and rapid processing compared to ceramic‐based composites. This review focuses majorly on the basic theory and principles behind piezoelectric energy harvesting (PEH) devices, followed by specified materials used for the different devices. Different structural configurations associated with fabrication of PEH devices are discussed in detail along with their major advantages and drawbacks. Numerous classes of piezoelectric polymers such as polyvinylidene fluoride, polylactic acid, cellulose, polyamides, polyurea, polyurethanes, and their composites used for energy harvesting applications as a productive alternative of lead‐based piezo‐ceramics, are extensively addressed and explored. Additionally, current global and Indian scenarios associated with PEH devices, major challenges associated with them, and the future perspective of such devices are also reported in this review.