Effect of aligned carbon nanotubes on electrical conductivity behaviour in polycarbonate matrix

This article reports effects of alignment of embedded carbon nanotubes in a polycarbonate polymer matrix under magnetic, direct and alternating current electric fields on the electrical properties of the resulting nanocomposites. Composites consisting of different quantities of carbon nanotubes in a polycarbonate matrix have been prepared using a solution casting technique. The effects of field strength and nanotube concentration on the resulted network structure and conductivity of the composites were studied by in situ optical microscopy, transmission electron microscopy and four-point probe technique. The results showed that the composites prepared in the presence of field had better conductivity than those of as-prepared composites. It was also concluded that the application of alternating current electric field and magnetic field in this system led to the formation of relatively continuing networks while direct current electric field only prevented agglomeration of the carbon nanotubes in the polycarbonate matrix and created relatively uniform distribution of nanotubes in the matrix.     

Morphological changes of carbon nanotubes in polyethylene matrices under oscillatory tests as determined by dielectrical measurements

By combining a high sensitive dielectric sensor into a parallel plate rheometer, the time evolution of the dielectric properties of polyethylene/carbon nanotube composites was measured in the molten state under oscillatory shear. Composites with single- (SWCNT) or multiwall (MWCNT) carbon nanotubes initially decrease its conductivity proportional to the oscillatory shear-strain applied. After this initial drop, some composites increase the conductivity under these non-quiescent conditions reflecting a possible shear-induced agglomeration process. The latter based on the complex permittivity spectrum showing a shortening in the CNT-CNT distances in these composites after shear. At concentrations below the electrical percolation threshold, the presence of both SWCNTs and MWCNTs reduces the DC conductivity of the molten matrices. This result shows that carbon nanotubes can act as a scavenger for impurities or additives present in commercial polyethylenes.     

碳纳米管增强铝基复合材料分散方法研究进展

碳纳米管与铝基体的结合,可以获得导电和导热性良好及综合力学性能优异的复合材料,有望成为新一代轻质高强、结构功能一体化的复合材料.在制备碳纳米管增强铝基复合材料过程中,碳纳米管的团聚将降低界面结合,诱发缺陷产生,导致性能大幅下降,因此,调控优化碳纳米管的分散状态、含量成为获取良好界面结合,获得高性能碳纳米管增强铝基复合材...     

Single-walled carbon nanotube incorporated novel three phase carbon/epoxy composite with enhanced properties

In the present work, single-walled carbon nanotubes were dispersed within the matrix of carbon fabric reinforced epoxy composites in order to develop novel three phase carbon/epoxy/single-walled carbon nanotube composites. A combination of ultrasonication and high speed mechanical stirring at 2000 rpm was used to uniformly disperse carbon nanotubes in the epoxy resin. The state of carbon nanotube dispersion in the epoxy resin and within the nanocomposites was characterized with the help of optical microscopy and atomic force microscopy. Pure carbon/epoxy and three phase composites were characterized for mechanical properties (tensile and compressive) as well as for thermal and electrical conductivity. Fracture surfaces of composites after tensile test were also studied in order to investigate the effect of dispersed carbon nanotubes on the failure behavior of composites. Dispersion of only 0.1 wt% nanotubes in the matrix led to improvements of 95% in Young's modulus, 31% in tensile strength, 76% in compressive modulus and 41% in compressive strength of carbon/epoxy composites. In addition to that, electrical and thermal conductivity also improved significantly with addition of carbon nanotubes.     

不同固化剂对MWNTs/EP复合材料导电性能的影响

采用己二胺和丙烯酰胺为原料,利用迈克尔加成反应合成了一种脂肪族胺类固化剂B,并用它与添加了多壁碳纳米管(MWNTs)的环氧树脂固化制备了B/MWNTs/环氧复合材料.利用傅立叶红外光谱、Novocontral宽频介电谱测试仪对合成固化剂B的结构及复合材料的介电性能进行了表征,并从电导、介电常数、损耗3个方面与常用固化剂DDS/MWNTs/环氧复合材料的性能进行了比较和理论分析.结果表明,固化剂种类对MWNTs/EP复合材料的电性能有较大的影响,使用含有导电π键的DDS作为固化剂要比长碳链的胺类固化剂B更容易达到逾渗点,即使添加少量MWNTs就可以达到好的电性能.     

Percolation threshold of carbon nanotubes filled unsaturated polyesters

This paper reports on the development of electrically conductive nanocomposites containing multi-walled carbon nanotubes in an unsaturated polyester matrix. The resistivity of the liquid suspension during processing is used to evaluate the quality of the filler dispersion, which is also studied using optical microscopy. The electrical properties of the cured composites are analysed by AC impedance spectroscopy and DC conductivity measurements. The conductivity of the cured nanocomposite follows a statistical percolation model, with percolation threshold at 0.026 wt.% loading of nanotubes. The results obtained show that unsaturated polyesters are a matrix suitable for the preparation of electrically conductive thermosetting nanocomposites at low nanotube concentrations. The effect of carbon nanotubes reaggregation on the electrical properties of the spatial structure generated is discussed.     

基于空间限域强制组装法制备短切碳纤维-碳纳米管/聚二甲基硅氧烷导电复合材料性能

采用空间限域强制组装（SCFNA）法制备短切碳纤维-碳纳米管/聚二甲基硅氧烷（SCF-CNTs/PDMS）导电复合材料,研究SCFNA方法制备SCF-CNTs/PDMS复合材料对断面形态变化、导电性能和力学性能的影响。结果表明,通过SCFNA制备的SCF-CNTs/PDMS导电复合材料得到了密实有效的导电网络,由于缩短了导电填料之间的距离,实现了在低浓度填料下增大复合材料的导电性能和力学性能。在填料总量不变的前提下,SCF/PDMS复合材料中添加少量的CNTs,SCF与CNTs之间能形成较好的协同作用。并发现SCF质量分数为8wt%、CNTs质量分数为2wt%的SCF-CNTs/PDMS复合材料与SCF质量分数为10wt%的SCF/PDMS复合材料相比,其导电性能提高了33%,力学性能提高了144%;在SCF/PDMS复合材料中添加较多的CNTs,由于CNTs之间发生团聚现象,SCF-CNTs/PDMS复合材料的导电性能和力学性能均有所下降。SCF质量分数为5wt%、CNTs质量分数为5wt%的SCF-CNTs/PDMS复合材料随着密炼转速由40 r/min逐步增加到80 r/min,CNTs团聚现象有所改善,但是由于扭矩的增大,SCF受到的剪切作用力增大,SCF大部分被搅碎,在导电复合材料中,SCF起主要连接导电网络的作用。因此,SCF质量分数为5wt%、CNTs质量分数为5wt%的SCF-CNTs/PDMS复合材料导电性能反而随着密炼转速的提高而降低。      

Correlation between dispersion state and electrical conductivity of MWCNTs/PP composites prepared by melt blending

Non-conductive polymers filled with conductive carbon nanotubes (CNTs) often do not show detectable conductivity due to poor dispersion of carbon nanotubes in the polymer matrix and the lack of conductive networks formed from CNTs. In this work, we attempted two ways to improve the dispersion of multi-walled carbon nanotubes (MWCNTs) in a polypropylene (PP) matrix: chemical modification of MWCNTs and addition of a master batch as a compatibilizer, followed by melt blending using a micro-compounder. The relationship between the dispersion state of MWCNTs and the electrical conductivity of the CNTs/PP composites have been investigated by controlling several factors such as CNTs modification, compatibilization by a master batch, melt mixing, and post-heat treatment. The enhanced interfacial adhesion between the CNTs and the polymer could improve the dispersion of CNTs but it could also reduce the electrical conductivity of the composites. Meanwhile, it is interestingly found that the post-heat treatment could increase the conductivity remarkably due to the connection of CNTs into networks. Thus, it is concluded that the balance between dispersion of CNTs and the formation of conductive networks plays an important role in enhancing the electrical conductivity of composites.     

Fracture toughness and electrical conductivity of epoxy composites filled with carbon nanotubes and spherical particles

The attainment of both high toughness and superior electrical conductivity of epoxy composites is a crucial requirement in some engineering applications. Herein, we developed a strategy to improve these performances of epoxy by combining the multi-wall carbon nanotubes (MWCNTs) and spherical particles. Two different types of spherical particles i.e. soft submicron-rubber and rigid nano-silica particles were chosen to modify the epoxy/MWCNT composites. Compared with the binary composites with single-phase particles, the ternary composites with MWCNTs and spherical particles offer a good balance in glass transition temperature, electrical conductivity, stiffness and strength, as well as fracture toughness, exhibiting capacities in tailoring the electrical and mechanical properties of epoxy composites. Based on the fracture surface analysis, the complicated interactions between multiscale particles and the relative toughening mechanisms were evaluated to explain the enhancement in fracture toughness of the ternary composites.     

PAPy/MWNTs复合材料的制备及其导电性能研究

通过原位化学氧化聚合法制备了聚3-乙酰基吡咯(PAPy)/多壁碳纳米管(MWNTs)复合材料。利用FT-IR、1 H-NMR、XRD、FE-SEM、FE-TEM、TGA等方法对单体和复合材料进行了结构和性能表征。红外光谱显示PAPy与MWNTs间并没有发生化学反应,MWNTs仅作为3-乙酰基吡咯(APy)单体聚合的模板。FE-SEM与FE-TEM分析表明,PAPy仅涂覆在MWNTs的外表面,涂覆厚度取决于APy与MWNTs间的质量比。热重分析表明,MWNTs可以提高PAPy/MWNTs复合材料的热稳定性。利用四探针法对样品进行了电导率测试,发现通过MWNTs与PAPy复合,可以显著地提高复合材料的导电性,并通过控制投料比,可以使复合材料的电导率接近MWNTs的电导率。     

The effect of geometric factor of carbon nanofillers on the electrical conductivity and electromagnetic interference shielding properties of poly(trimethylene terephthalate) composites: a comparative study

In this study, the effects of filler geometry on the electrical conductivity and electromagnetic interference (EMI) shielding properties of poly(trimethylene terephthalate) (PTT) composites filled with graphene nanosheets (GNSs), carbon nanotubes (CNTs), and GNS–CNT hybrid nanofillers have been investigated. The GNSs, CNTs, and hybrid GNS–CNT were well dispersed in the PTT matrix using a simple coagulation process. GNSs were prepared from graphene oxide (GO) through hydrazine reduction, and thermal reduction of GO at two different temperatures of 1050 and 1500 °C. PTT filled with different aspect ratios and oxygen functional groups of GNS were also prepared in order to compare the electrical conductivity and EMI shielding properties. The aspect ratios of GNSs and CNTs were estimated by using an ellipsoid model. Percolation scaling laws were applied to the magnitudes of conductivity to reveal the percolation network and filler dispersion. The percolation exponent of the PTT/GNS composites was larger than that of the PTT/CNT composites. The percolated filler–filler network at which the percolation exponent changed was correlated with the filler geometric structure. GNS–CNT hybrid nanofillers formed a complex double brush structure in the PTT/GNS–CNT composites. The geometric structure, aspect ratio, and intrinsic conductivity of carbon nanofillers affected the electrical percolation threshold and EMI shielding efficiency of the composites.     

Electrical conductivity and mechanical properties of multiwalled carbon nanotube-reinforced polypropylene nanocomposites

In this paper, the electrical conductivity and mechanical properties such as elastic modulus of multiwalled carbon nanotubes (MWCNTs) reinforced polypropylene (PP) nanocomposites were investigated both experimentally and theoretically. MWCNT-PP nanocomposites samples were produced using injection mold at different injection velocities. The range of the CNT fillers is from 0 up to 12?wt%. The influence of the injection velocity and the volume fraction of CNTs on both electrical conductivity and mechanical properties of the nanocomposites were studied. The injection speed showed some effect on the electrical conductivity, but no significant influence on the mechanical properties such as elastic modulus and stress-strain relations of the composites under tensile loading. Parallel to the experimental investigation, for electrical conductivity, a percolation theory was applied to study the electrical conductivity of the nanocomposite system in terms of content of nanotubes. Both Kirkpatrick (Rev Mod Phys 45:574?C588, 1973) and McLachlan et?al. (J Polym Sci B 43:3273?C3287, 2005) models were used to determine the transition from low conductivity to high conductivity in which designates as percolation threshold. It was found that the percolation threshold of CNT/PP composites is close to 3.8?wt%. For mechanical properties of the system, several micromechanical models were applied to elucidate the elastic properties of the nanocomposites. The results indicate that the interphase between the CNT and the polymers plays an important role in determining the elastic modulus of the system.     

Synthesis of nano-carbon (nanotubes,nanofibres, graphene) materials

In the present study, we report the synthesis of carbon nanotubes (CNTs) using a new natural precursor: castor oil. The CNTs were synthesized by spray pyrolysis of castor oil-ferrocene solution at 850°C under an Ar atmosphere. We also report the synthesis of carbon nitrogen (C-N) nanotubes using castor oil-ferrocene-ammonia precursor. The as-grown CNTs and C-N nanotubes were characterized through scanning and transmission electron microscopic techniques. Graphitic nanofibres (GNFs) were synthesized by thermal decomposition of acetylene (C₂H₂) gas using Ni catalyst at 600°C. As-grown GNFs reveal both planar and helical morphology. We have investigated the structural and electrical properties of multi-walled CNTs (MWNTs)-polymer (polyacrylamide (PAM)) composites. The MWNTs-PAM composites were prepared using as purified, with ball milling and functionalized MWNTs by solution cast technique and characterized through SEM. A comparative study has been made on the electrical property of these MWNTs-PAM composites with different MWNTs loadings. It is shown that the ball milling and functionalization of MWNTs improves the dispersion of MWNTs into the polymer matrix. Enhanced electrical conductivity was observed for the MWNTs-PAM composites. Graphene samples were prepared by thermal exfoliation of graphite oxide. XRD analysis confirms the formation of graphene.     

Dispersion and reinforcing mechanism of carbon nanotubes in epoxy nanocomposites

Carbon nanotube based epoxy composites have been fabricated at room temperature and refrigeration process using sonication principle. Flexural moduli, electrical conductivity, glass transition temperature of epoxy resin as well as nanocomposite samples have been determined. Distribution behaviour of carbon nanotubes in the epoxy matrix was examined through scanning electron microscopy. Composite samples showed better properties than resin samples due to strengthening effect of the filled nanotubes. Refrigerated nanocomposites obtained increasing mechanical property because of better dispersion due to low temperature settlement of polymers. Improvement of electrical conductivity was due to the fact that aggregated phases form a conductive three-dimensional network throughout the whole sample. The increasing glass transition temperature was indicative of restricting movement of polymer chains that ascribe strong interaction presented between carbon nanotubes and epoxy chains that was again supplemented by Raman study and SEM.     

多壁碳纳米管复合材料在26.5～40 GHz频段的电磁性能

采用玻璃布作为分散载体制备多壁碳纳米管/玻璃纤维/环氧树脂复合材料,研究了在26.5～40 GHz频段,多壁碳纳米管的含量对复合材料的电磁参数及电导率的影响,同时测量了复合材料在该波段的电磁波反射率。研究结果表明:随多壁碳纳米管含量的增加,其介电常数实部和虚部随之增加,介电损耗角正切提高了4倍。复合材料的磁导率随多壁碳纳米管含量的提高变化不明显,呈弱磁性。复合材料的电导率随多壁碳纳米管含量的增加,由原来的绝缘体变为半导体。另外,在26.5～40 GHz频段内多壁碳纳米管复合材料对电磁波的隐身效果不好。      

多壁碳纳米管/聚偏氟乙烯高介电常数复合材料的制备与性能

为制备具有高介电常数的复合材料,采用注射成型法制备了原始多壁碳纳米管(P-MWCNTs)/聚偏氟乙烯(PVDF)复合材料和石墨化多壁碳纳米管(G-MWCNTs)/PVDF复合材料。然后,对P-MWCNTs和G-MWCNTs进行了Raman光谱表征,对MWCNTs/PVDF复合材料进行了断面形貌、力学性能和电学性能测试。结果表明:G-MWCNTs比P-MWCNTs具有更高的纯度和结晶度,两种不同的MWCNTs都能均匀分散在PVDF基体中,添加MWCNTs会显著影响PVDF的力学行为。MWCNTs/PVDF复合材料的介电性能随MWCNTs含量的增加而提高,与P-MWCNTs相比,G-MWCNTs有效降低了复合材料的渗流阈值。当频率为100 Hz时,纯PVDF的介电常数为7.0;当P-MWCNTs的含量为5wt%时,复合材料的介电常数为23.8;当G-MWCNTs的含量为5wt%时,复合材料的介电常数高达105.0。注射成型法制备的MWCNTs/PVDF复合材料仍保持相对较低的电导率,进而导致复合材料的能量损耗较低,对电荷存储应用具有重要意义。     

碳纳米管/丁苯橡胶复合材料的电学性能

采用喷雾干燥法可制备不同配比的碳纳米管（Carbon nanotubes,CNTs）/粉末丁苯橡胶复合材料,观察CNTs在橡胶基体中的分散情况,检测复合材料的导电性能及介电性能,并进行了简要的理论分析。结果表明:CNTs在橡胶基体中获得了充分均匀的分散,有利于CNTs改性补强作用的发挥。与纯胶样品及填充炭黑（Carbon black,CB）样品相比, 填充CNTs样品在8~18GHz下具有较高的介电常数及低介电损耗。随着CNTs加入量的增加,CNTs/粉末丁苯橡胶复合材料的电导率逐渐升高,当CNTs加入量为60phr（per hundred rubber）时,与纯胶样品及添加60phr CB样品相比,电导率提高近10个数量级;复合材料内部导电同时存在隧道导电机制和渗逾导电机制。采用喷雾干燥法制备的CNTs/粉末丁苯橡胶复合材料,将是一种综合性能良好的新型纳米复合材料,有望在抗静电橡胶、电磁屏蔽及介电材料等领域获得应用。      

Electrical conductivity of water- based nanofluids prepared with graphene – carbon nanotube hybrid

Graphene, Carbon Nanotubes and their hybrids are receiving considerable attention in energy storage devices due to their unique properties. The present study reports the synthesis of Graphene–Carbon Nanotube hybrid having variable ratios of the constituting nanomaterials by employing two different chemical routes to explore their potential in energy storage devices. To study the structure and morphology of synthesized nanomaterials, all samples were characterized by high resolution imaging and spectroscopy techniques. Electrical conductivity of synthesized Graphene-Carbon Nanotube hybrid, graphene oxide and carbon nanotubes was measured by two probe method to study whether the conductivity of hybrid is greater than that of graphene and carbon nanotubes. It was observed that hybrid exhibited excellent stability due to strong π-π interaction between carbon nanotubes and graphene oxide sheets. The maximum electrical conductivity was obtained for the hybrid in which amount of graphene oxide was more than that of multiwalled carbon nanotubes. Moreover, the results of electrical conductivity demonstrated that the structure of hybrid plays significant role in improving its properties.     

Effect of size and shape of metal particles to improve hardness and electrical properties of carbon nanotube reinforced copper and copper alloy composites

Utilizing the extra-ordinary properties of carbon nanotube (CNT) in metal matrix composite (MMC) for macroscopic applications is still a big challenge for science and technology. Very few successful attempts have been made for commercial applications due to the difficulties incorporating CNTs in metals with up-scalable processes. CNT reinforced copper and copper alloy (bronze) composites have been fabricated by well-established hot-press sintering method of powder metallurgy. The parameters of CNT–metal powder mixing and hot-press sintering have been optimized and the matrix materials of the mixed powders and composites have been evaluated. However, the effect of shape and size of metal particles as well as selection of carbon nanotubes has significant influence on the mechanical and electrical properties of the composites. The hardness of copper matrix composite has improved up to 47% compared to that of pure copper, while the electrical conductivity of bronze composite has improved up to 20% compared to that of the pure alloy. Thus carbon nanotube can improve the mechanical properties of highly-conductive low-strength copper metals, whereas in low-conductivity high-strength copper alloys the electrical conductivity can be improved.     

Effect of different carbon fillers and dopant acids on electrical properties of polyaniline nanocomposites

Electrically conducting nanocomposites of polyaniline (PANI) with carbon-based fillers have evinced considerable interest for various applications such as rechargeable batteries, microelectronics, sensors, electrochromic displays and light-emitting and photovoltaic devices. The nature of both the carbon filler and the dopant acid can significantly influence the conductivity of these nanocomposites. This paper describes the effects of carbon fillers like carbon black (CB), graphite (GR) and muti-walled carbon nanotubes (MWCNT) and of dopant acids like methane sulfonic acid (MSA), camphor sulfonic acid (CSA), hydrochloric acid (HCl) and sulfuric acid (H₂SO₄) on the electrical conductivity of PANI. The morphological, structural and electrical properties of neat PANI and carbon–PANI nanocomposites were studied using scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FT–IR), UV–Vis spectroscopy and the four-point probe technique, respectively. Thermogravimetric analysis (TGA) and X-ray diffraction (XRD) studies were also conducted for different PANI composites. The results show that PANI and carbon–PANI composites with organic acid dopants show good thermal stability and higher electrical conductivity than those with inorganic acid dopants. Also, carbon–PANI composites generally show higher electrical conductivity than neat PANI, with highest conductivities for PANI–CNT composites. Thus, in essence, PANI–CNT composites prepared using organic acid dopants are most suitable for conducting applications.