Nano-Al2O3/PANI composites with high negative permittivity

Polyaniline (PANI) composites filled with ferroferric oxide and barium titanate were discovered to have metamaterial characteristics in recent years. In this paper, based on micron-Al₂O₃/PANI composites with negative permittivity, the dielectric properties of nano-Al₂O₃/PANI composites were studied. Nano-Al₂O₃/PANI composites had negative permittivity, which was considerably higher than that of PANI and micron-Al₂O₃/PANI composites. The higher negative permittivity was caused by the better dispersibility of nano-Al₂O₃, resulting in the enlargement of polarization voltage on a greater range of PANI molecular chain. Moreover, nano-Al₂O₃/PANI composite with 5 wt% nano-Al₂O₃ has the largest negative permittivity (−2.24 × 10⁶) that has not been reported so far in oxide/PANI composites.     

Negative permittivity and negative permeability of multi-walled carbon nanotubes/polypyrrole nanocomposites

Multi-walled carbon nanotubes(MWCNTs)/polypyrrole(PPy) nanocomposite particles were synthesized by in-situ polymerization. Negative permittivity and negative permeability appeared simultaneously in MWCNTs/PPy nanocomposites with different content of MWCNTs. It was found from SEM analysis that MWCNTs/PPy nanocomposite particles were randomly packed with a large number of micropores, and formed a lot of conductive loops around the micropores, some MWCNTs could be cross the micropores and increase the number of conductive loops. In the meantime, MWCNTs themselves in MWCNTs/PPy composite also formed many conductive networks. The negative permittivity behavior stem from the plasma oscillation of delocalized electrons in the conductive networks, and the negative permeability was attributed to the diamagnetic response of ring currents in the plentiful conductive loops. This study should initially find a double negative metamaterial in polymer composites.     

Effect of Multiwall Carbon Nanotubes on Electrical and Structural Properties of Polyaniline

Polyaniline (PANI) and PANI/CNT (multiwall carbon nanotubes, CNT) composites were prepared using an oxidative chemical polymerization method with ammonium persulfate and dodecyl benzene sulfonic acid as the oxidizing agent and surfactant, respectively. Fourier-transform infrared spectroscopy spectra illustrate the presence of PANI in the composite and show that some interaction exists between PANI and CNT. Embedding of CNT in the PANI matrix is confirmed by scanning electron micrography. Conductivity of the PANI/CNT composites was higher than that of pure PANI, and the maximum conductivity obtained was 4.44?S/cm at 20?wt.% CNT.     

A Facile Synthesis of a Palladium-Doped Polyaniline-Modified Carbon Nanotube Composites for Supercapacitors

Supercapacitors have evolved as the premier choice of the era for storing huge amounts of charge in the field of energy storage devices, but it is still necessary to enhance their performance to meet the increasing requirements of future systems. This could be achieved either through advancing the interfaces of the material at the nanoscale or by using novel material compositions. We report a high-performance material composition prepared by combining a transition metal (palladium)-doped conductive polymer with multiwalled carbon nanotubes (MWCNTs). MWCNTs/palladium-doped polyaniline (MWCNTs/Pd/PANI) composites and multiwalled carbon nanotube/polyaniline (MWCNTs/PANI) composites (for comparison) were prepared via in situ oxidative polymerization of aniline monomer. The reported composites were characterized by Fourier-transform infrared (FTIR), x-ray diffraction (XRD), field-emission scanning electron microscopy (FESEM), and transmission electron microscopy (TEM) studies. FESEM and TEM studies indicated the narrow size distribution of the π-conjugated polymer-protected palladium nanoparticles on the surface of the carbon nanotubes. All the electrochemical characterizations were executed using a three-electrode system in 1 M H₂SO₄ electrolyte. Cyclic voltammetry (CV) analysis was performed to observe the capacitive performance and redox behavior of the composites. The ion transfer behavior and cyclic stability of the composites were investigated by electrochemical impedance spectroscopy (EIS) analysis and cyclic charge–discharge (CCD) testing, respectively. The MWCNTs/Pd/PANI composite was found to exhibit an especially high specific capacitance value of 920 F/g at scan rate of 2 mV/s.     

Influence of electronic type of SWNTs on the thermoelectric properties of SWNTs/PANI composite films

Single-walled carbon nanotubes (SWNTs) have emerged as one of the leading additives for improving the thermoelectric properties of organic materials due to their unique structure and excellent electronic transport properties. However, since as-grown SWNTs possess different chirality, it is of high interest to determine the influence of electronic type of SWNTs on the thermoelectric properties of SWNTs/PANI composite films. Herein, we utilized metallic SWNTs (SWNT-M) and semiconducting SWNTs (SWNT-S) to prepare SWNTs/PANI composite films and studied their thermoelectric properties, respectively. Experimentally, the maximum thermoelectric power factor reached 51 μW m⁻¹ K⁻² for the 19 wt% SWNT-S/PANI composite films, while that value was only 16 μW m⁻¹ K⁻² for the 19 wt% SWNT-M/PANI composite films. The better power factor of SWNT-S/PANI composite films may be attributed to the more significantly enhanced Seebeck coefficient resulting from the effective energy filtering effect at the interfaces between SWNT-S and PANI. Our results reveal the influence of electronic type of SWNTs on the thermoelectric properties of composites, which will drive ongoing efforts to utilize SWNTs as fillers in nanocomposites for optimal thermoelectric properties.     

In situ observation of the growth mechanisms of carbon nanotubes under diverse reaction conditions

We report in situ environmental transmission electron microscope observations of the nucleation and growth of multi-wall and single-wall carbon nanotubes formed by the catalytic decomposition of acetylene (C2H2) on Ni/SiO2 catalyst. The growth rate, structure and morphology of the carbon nanotubes formed depended upon reaction temperature and pressure. Under 20-100 mTorr of gas pressures at 480 degrees C, serpentine-shaped or zigzag, multi-wall carbon nanotubes grew at an average rate of 35-40 nm sec(-1). At pressures <10 mTorr at the same temperature, straight single-wall carbon nanotubes with nearly uniform diameters (approximately 3.5 nm) formed at average growth rates of 6-9 nm sec(-1). The growth of both straight and serpentine carbon nanotubes tends to proceed at non-uniform rates, with frequent pauses followed by growth spurts. The nanotubes frequently contained sharp bends that turned the nanotube axis by approximately 60 degrees and approximately 120 degrees. We conjecture that the bends are related to the change in growth direction that is dictated by the crystallographic orientation of the catalyst particle. The rotations of the nanometer-sized catalyst particle may be caused by transient melting-recrystallization events caused by local thermal variations. The nanotube attempts to follow the preferred growth direction, while simultaneously attempting to maintain a seamless 3-coordinated graphene wall. This latter condition is most easily satisfied by the introduction of pentagon-heptagon defect pairs dissociated to the opposite sides of the nanotube creating the 60 degree bend.     

The effect on the impedance characteristics of the metal oxides (Al2o3 and Zno) doping into polyaniline

In this study, the doping metal oxides; ZnO and Al₂O_3, (MO for short) into poly (aniline) (PANI) how that affects the dielectric properties have been investigated by the impedance analysis technique. PANI, PANI-Al₂O₃ and PANI-ZnO were synthesized by chemical oxidative polymerization. Both FTIR and SEM are used to characterize the structure and morphologies of these composites. Dielectric properties of PANI and PANI–MO composites have been performed in the frequency range 100 Hz −1 MHz. It was seen that the values of the dielectric constant and impedance increase with doping Al₂O₃ and ZnO into PANI. Absorption coefficient (α) and relaxation times (τ) parameters were calculated and it is revealed that the relaxation mechanism changed significantly by the doping of metal oxide into PANI. Moreover, the conductivity properties of PANI-MO composites were performed and it is seen that “s” parameter value correlated Barrier Hoping (CBH) Mechanism.     

Cover Picture: Preparation of Rectangular WO3·H2O Nanotubes Under Mild Conditions (Adv. Funct. Mater. 11/2007)

The synthesis of WO₃ · H₂O nanotubes under mild conditions is reported by Limin Wu and co‐workers, of Fudan University, P.R. China on p. 1790. The synthesis is carried out with the aid of polyaniline (PANI). The PANI molecules are intercalated into tungsten oxide layers to provide a driving force for the formation of nanotubes from nanosheets. By this approach, the nanosheets can be directly rolled into nanotubes. This method could be applied to many other materials that possess layered/lamellar structures for forming nanotubes. WO₃·H₂O nanotubes are successfully synthesized with the aid of intercalated polyaniline (PANI) under relatively mild conditions. More interestingly, the WO₃·H₂O nanotubes have a rectangular cross‐section structure formed through a rolling mechanism. Scanning electron microscopy, transmission electron microscopy, X‐ray diffraction, thermogravimetric analysis, Fourier‐transform infrared analysis, UV‐vis‐near‐IR spectroscopy, selected‐area electron diffraction, and vibrating‐sample magnetometry analysis are employed to characterize the morphology, structure, and properties of the nanotubes.     

Fabrication of nylon-6/carbon nanotube composites

A new technique to fabricate nylon-6/carbon nanotube (PA6/CNT) composites is presented. The method involves a pretreatment of carbon nanotubes synthesized by catalytic pyrolysis of hydrocarbon and an improved in-situ process for mixing nanotubes with the nylon 6 matrix. A good bond between carbon nanotubes and the nylon-6 matrix is obtained. Mechanical property measurements indicate that the tensile strength of PA6/CNT composites is improved significantly while the toughness and elongation are somewhat compromised. Scanning electron microscopy (SEM) analysis of the fractured tensile specimens reveals cracking initiated at the wrapping of the CNTs PA6 layer/PA6 matrix interface rather than at the PA6/CNT interface.     

High-resolution electron microscopy of multi-wall carbon nanotubes in the subcutaneous tissue of rats

The atomic structure of multi-wall carbon nanotubes (MWCNTs) implanted in the subcutaneous tissue of rats was examined by means of high-resolution transmission electron microscopy (HRTEM). Clusters of the MWCNTs implanted in the subcutaneous tissue were well recognized by the TEM observations. It was indicated that some nanotubes were taken in phagocytes after the 1-year implantation. The deterioration of crystalline structure of the nanotubes in phagocytes was shown by the HRTEM observation. It was suggested that the deterioration of the nanotubes was due to the peeling of the outer graphene layers in the phagocytes.     

Synthesis and morphological characterization of PMMA/polyaniline nanofiber composites

Poly (methyl methacrylate) (PMMA)/Polyaniline nanofibers composite films were prepared by solution casting. Doped polyaniline self-assembled nanofibers (PANFs) were synthesized by interfacial polymerization performed in an aqueous HCl/dichloromethane biphasic system in the presence of ammonium peroxydisulfate as oxidant agent. Sodium dodecyl sulfate (SDS) was added to the organic phase in order to verify possible modification the morphology the nanostrucutures when compared with previous reports. Treatment in an ultrasonic bath of PANFs on butanone resulted in a green dispersion (up to 250 mg/dL). Dispersed PANFs were then combined with PMMA/butanone solution. Additional sonication and posterior film cast from solution procedures resulted in slight green PMMA/PANFs 0.15-0.30% (wt/wt) composite films. Film composites were characterized by UV-Vis spectroscopy and Scanning Electron Microscopy (SEM). PANFs powder was investigated by (SEM).An investigation by viscosity method on molecular structure of neat PMMA exposed to ultrasonic irradiation up to 2 h showed small change (<5%) in the viscosity-average molar mass, Mv (≈100 kg/mol). It suggests that mechanical degradation by cavitation does not occur on PMMA under those conditions. Thus, ultrasonic bath treatment is a simple, accessible method for mitigating solubility problems of PANI doped with inorganic acids and improving quality of low concentration PMMA/PANI composites. Application of these composites relies on the radiolytic stabilization effects of PANI on PMMA matrix.     

碳纳米管微电极的直流介质阻挡放电特性

研究了一种基于碳纳米管尖端的直流介质阻挡放电(DBD)微结构,使用MEMS加工工艺制作出深宽比0.5的侧壁相对的叉指状金属电极,在电极上电泳多壁碳纳米管,采用真空磁控溅射沉积二氧化硅介质层。在大气压下测试了所制备的DBD微结构样品的直流放电基本特性。实验结果表明,在几伏特的直流加载电压下即可检测到纳安量级的放电电流,并且放电电流对人体呼吸和环境气体变化有明显响应。放电起始电压小于10V并显现出明显的抑制电流自由增长的DBD放电特征,但电流下降持续时间达102～103s量级,大于常规常压DBD时间,显示出碳纳米管尖端的特异效应。     

碳基气凝胶复合材料电磁波吸收材料研究进展

随着无线电通信技术和各种电子设备的广泛应用,电磁污染日益严重,具有三维多孔结构的电磁波吸收材料成为科学研究的热点。总结了碳基气凝胶复合材料的研究进展,详细介绍了石墨烯气凝胶、生物质衍生的碳气凝胶和聚合物衍生的碳气凝胶的多种制备方法,碳气凝胶与磁性颗粒、碳化硅、碳纳米管和MXene复合而成的复合碳基气凝胶吸波材料的吸波性能。简要阐述了吸波材料的损耗机理,讨论了碳基气凝胶复合材料的组分、微观结构和损耗机制对吸波性能的影响。最后,就目前研究现状总结了碳基气凝胶复合材料在制备和性能提升方面的挑战,展望了碳基气凝胶复合材料的研究重点和发展方向。     

基于金属基复合材料的硅通孔热应力仿真分析

硅通孔(TSV)技术是三维集成电路中的关键技术,对信号传输以及热量的传导起到关键的作用,其热可靠性的问题一直都是研究热点。基于Comsol Mulitiphsics平台,通过有限元仿真分析,研究了金属基复合材料对TSV热应力的影响。并进一步研究了在不同通孔直径以及不同TSV高度下,碳纳米管(CNTs)、碳纳米管铝(CNTs/Al)以及碳纳米纤维铜(CNFs/Cu)等复合材料和传统金属材料的等效热应力情况。结果表明:与传统金属材料相比,金属基复合材料CNTs/Al以及CNFs/Cu均能有效降低TSV的热应力,提高TSV的热可靠性;并且对于CNTs含量不同的金属基复合材料,其TSV的等效热应力也会有所不同,需综合考虑合理选择CNTs的含量。     

Magnetodielectric Microwave Radiation Absorbent Materials and Their Polymer Composites

Functional radiation absorbent materials (RAMs) can transform incident microwave energy into heat energy, hence being essential to impede reflections of microwaves generated by modern radars in military, aerospace, and commercial applications. For such applications, use of composites is imperative to maintain an optimum bandwidth, enhance the magnetoelectric functional activity, ensure a flexible design, and reduce weight, which can be achieved by tuning the volume fractions of such materials. Use of ferrites is widely recommended for microwave (MW) suppression due to their appropriate magnetodielectric characteristics. This review first describes the requirements for an ideal MW absorber and accurate measurements for quantification of MW absorption. Then, the significance, applications, approaches, and experimental developments of magnetodielectric polymer composite RAMs are presented. Moreover, such composites facilitate exploration of nanoscale functional properties to achieve efficient RAMs. The permeability and permittivity at microwave frequencies, magnetic properties induced by unique elemental doping mechanisms, as well as physical and chemical properties of these composites are also presented. The resonance-dependent absorption condition for different families of magnetic ferrites, as well as the dependence of their magnetic properties on the resonant frequency and their absorption bandwidth (spinels up to 30 GHz, hexaferrites 1 GHz to 100 GHz), are presented for applications. Furthermore, magnetodielectric composites decorated with carbon fillers (carbon nanotubes/multiwall carbon nanotubes, graphene, reduced graphene oxide, etc.) with enhanced microwave absorption properties are discussed. Additionally, core–shell magnetodielectric materials are also discussed in detail. Finally, this review highlights the importance of magnetodielectric polymer composites decorated with conducting materials and core–shell magnetodielectric materials as effective broadband RAMs achieving the primary application requirement of broadband absorption of at least ?10 dB with reduced thickness.     

碳基纳米吸波材料制备的研究进展

为探索民用电磁屏蔽和军用隐形碳基高性能吸波材料的制备,研究了碳纳米管和磁性金属复合,碳纳〖JP2〗米管和铁氧体复合,碳纳米管/聚合物复合,碳、石墨基复合等碳基吸波材料的不同复合和制备方法,比较了其反射损耗等不同的特点、影响因素和性能特点及其相关应用。结果表明,多元复合、低维化、工艺优化是其制备的有效途径。     

掺杂态可溶性聚苯胺/p-PDA功能化MWNTs复合材料的TEM及表面分析

通过透射电子显微镜（TEM）和X-射线光电子能谱（XPS）,研究了对苯二胺（p-PDA）功能化多壁碳纳米管（p-MWNTs）的形貌及表面化学状态、HCl掺杂PANI/p-MWNTs复合材料的形成过程、DBSA二次掺杂PANI/p-MWNTs和SPAN/p-MWNTs复合材料溶解在NMP和水中的结构。研究结果表明：纯化MWNTs经p-PDA功能化反应后,苯胺基团以3.7%的含量通过酰胺键连接到p-MWNTs表面石墨结构的缺陷点上;p-MWNTs表面的苯胺基团被氧化后引发原位聚合,支配了PANI包覆层内层和p-MWNTs两端PANI大分子的形成;当核-壳结构的DBSA二次掺杂PANI/p-MWNTs复合材料和SPAN/p-MWNTs复合材料分别溶解在NMP和水中时,大部分外层可溶性聚苯胺溶解在溶剂中,包覆层内层的大分子溶胀和缠结在p-MWNTs表面,借助大分子的溶解性和p-MWNTs与大分子间的连接作用,使DBSA二次掺杂PANI/p-MWNTs复合材料和SPAN/p-MWNTs复合材料分别在NMP和水中获得较高的溶解稳定性。     

Graphene and Carbon Nanotube Auxetic Rubber Bionic Composites with Negative Variation of the Electrical Resistance and Comparison with Their Nonbionic Counterparts

Microorganism metabolic activity can facilitate the formation of cellular material systems that have unusual mechanical and physical properties. In the living world microorganisms are commonly used for preparing porous food by fermentation; here carbon nanotubes, graphene nanoplatelets, and a mix of them are dispersed in liquid silicone rubber with single‐cell fungi of commercial beer yeast. The fermentation of such microorganisms during the gelling of the silicone matrix results in bionic composites with buckled/collapsed cells that infer, as rationalized with an analytical model and excluded in a abiotic experimental comparison, auxetic properties. During stretching it is found that the Poisson's ratio of such composites changes sign, from negative to positive, and the variation of the electrical resistance is negative. In addition to the conductivity increment, a general increment of the stretchability and damage resistance with respect to the composites prepared by abiotic process is observed. Bionic composites, even if in their infancy, can thus be multifunctional and superior to their traditional/abiotic counterparts.     

导电聚苯胺电磁屏蔽复合材料研究及进展

介绍导电聚苯胺（PANI）及其复合材料的特点、制备方法、分类、性能优化方法,讨论了掺杂剂的种类、PH值、反应温度等影响聚苯胺复合材料电磁屏蔽性能的因素,并提出要进一步发展需要解决PANI的溶熔性和加工性问题,改善PANI的结构。     

酞菁裂解法制备定向碳纳米管阵列及其场发射性能研究

碳纳米管作为一种新型的光电材料有着广泛的应用,可用于平板显示器中的电子发射器件。定向碳纳米管阵列是碳纳米管的一种取向形态,具有其独特的性质。与缠绕无序的碳纳米管相比,定向碳纳米管更易分散、测量和应用。文章在低压条件下采用酞菁铁高温裂解法,在800～1000℃,以石英玻璃为基底,制备了大面积高度定向的碳纳米管。通过SEM和TEM对定向碳纳米管的结构进行分析。结果表明该法制备的碳纳米管长20μm,管径40～70nm,为竹节状结构的多壁碳纳米管。实验中发现系统真空度和生长温度都对定向碳纳米管生长有影响。通过对该碳纳米管进行场发射测试,结果表明此定向碳纳米管的开启电压仅为0.67V.μm-1(I=1μA),阈值电压为2.5V.μm-1,具有良好的场发射性能。