Synthesis and characterization of carbon nanotube/polypyrrole core–shell nanocomposites via in situ inverse microemulsion

We demonstrate here a feasible approach to the preparation of multiwalled carbon nanotube (MWNT)/polypyrrole (PPy) core–shell nanowires by in situ inverse microemulsion. Transmission electron microscopy and scanning electron microscopy showed that the carbon nanotubes were uniformly coated with a PPy layer with a thickness of several to several tens of nanometers, depending on the MWNT content. Fourier transform infrared spectra suggested that there was strong interaction between the π‐bonded surface of the carbon nanotubes and the conjugated structure of the PPy shell layer. The thermal stability and electrical conductivity of the MWNT/PPy composites were examined with thermogravimetric analysis and a conventional four‐probe method. In comparison with pure PPy, the decomposition temperature of the MWNT/PPy (1 wt % MWNT) composites increased from 305 to 335 °C, and the electrical conductivity of the MWNT/PPy (1 wt % MWNT) composites increased by 1 order of magnitude. The current–voltage curves of the MWNT/PPy nanocomposites followed Ohm's law, reflecting the metallic character of the MWNT/PPy nanocomposites. The cyclic voltammetry measurements revealed that PPy/MWNT composites showed an enhancement in the specific charge capacity with respect to that of pure PPy. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 6105–6115, 2005     

溴吸附对碳纳米管导电性能的提高

通过溴蒸气的吸附, 提高多壁碳纳米管(MWNT)的本征导电性能,加溴多壁碳纳米管的电导率提高3倍. 通过拉曼光谱, 紫外可见光谱, 红外吸收光谱, 近红外吸收光谱和X光电子能谱等方法研究, 结果表明: 溴与多壁碳纳米管之间存在共轭作用, 使多壁碳纳米管表面的电子云分布发生了变化, 导致空穴载流子的产生, 增加了载流子浓度, 提高了多壁碳纳米管的导电性能.     

Positive Temperature Coefficient Characteristics of Multi-walled Carbon Nanotube Filled Polyvinylidene Fluoride Nanocomposites

Composites of polyvinylidene fluoride (PVDF) and multi-wall carbon nanotubes (MWNT) were prepared by a melt mixing process. Temperature dependence of electrical properties of the nanocomposites was investigated for composites containing different amounts of MWNT. An obvious positive temperature coefficient was observed. It was found that resistivity of the composites was decreased with increasing MWNT content and the electrical percolation threshold was formed at 3 wt% MWNT, which were caused by the formation of conductive chains in the composites. The mechanism of the positive temperature coefficient behavior of the nanocomposites is discussed. The rheological results showed that the materials experience a fluid–solid transition at the composition of 2 wt%, beyond which a continuous MWNT network forms throughout the matrix leading to a percolated network structure, which further indictes the nanotubes were dispersed uniformaly, in the PVDF matrix.     

Electrical properties study of multi-walled carbon nanotubes/hybrid-glass nanocomposites

Electrical properties of multi-walled carbon nanotubes (MWNTs)/hybrid-glass nanocomposites prepared by the fast-sol–gel reaction were investigated in light of percolation theory. A good correlation was found between the experimental results and the theory. We obtained a percolation threshold ? _c  = 0.22 wt%, and a critical exponent of t = 1.73. These values are reported for the first time for a silica-based system. The highest conductivity measured on the MWNT/hybrid-glass nanocomposites was σ ≈ 10^?3(Ω cm)^?1 for 2 wt% carbon nanotube (CNT) loading. The electrical conductivity was at least 12 orders of magnitude higher than that of pure silica. Electrostatic force microscopy and conductive-mode atomic force microscopy studies demonstrated conductivity at the micro-level, which was attributed to the CNT dispersed in the matrix. It appears that the dispersion in our MWNT/hybrid-glass system yields a particularly low percolation threshold compared with that of a MWNT/silica-glass system. Materials with electrical conductivities described in this work can be exploited for anti-static coating.     

Influences of poly(lactic acid)‐grafted carbon nanotube on thermal,mechanical, and electrical properties of poly(lactic acid)

Poly(lactic acid)‐grafted multiwalled carbon nanotubes (MWNT‐g‐PLA) were prepared by the direct melt‐polycondensation of L ‐lactic acid with carboxylic acid‐functionalized MWNT (MWNT‐COOH) and then mixed with a commercially available neat PLA to prepare PLA/MWNT‐g‐PLA nanocomposites. Morphological, thermal, mechanical, and electrical characteristics of PLA/MWNT‐g‐PLA nanocomposites were investigated as a function of the MWNT content and compared with those of the neat PLA, PLA/MWNT, and PLA/MWNT‐COOH nanocomposites. It was identified from FE‐SEM images that PLA/MWNT‐g‐PLA nanocomposites exhibit good dispersion of MWNT‐g‐PLA in the PLA matrix, while PLA/MWNT and PLA/MWNT‐COOH nanocomposites display MWNT aggregates. As a result, initial moduli and tensile strengths of PLA/MWNT‐g‐PLA composites are much higher than those of neat PLA, PLA/MWNT, and PLA/MWNT‐COOH, which stems from the efficient reinforcing effect of MWNT‐g‐PLA in the PLA matrix. In addition, the crystallization rate of PLA/MWNT‐g‐PLA nanocomposites is faster than those of neat PLA, PLA/MWNT, and PLA/MWNT‐COOH, since MWNT‐g‐PLA dispersed in the PLA matrix serves efficiently as a nucleating agent. It is interesting that, unlike PLA/MWNT nanocomposites, surface resistivities of PLA/MWNT‐g‐PLA nanocomposites did not change noticeably depending on the MWNT content, demonstrating that MWNTs in PLA/MWNT‐g‐PLA are wrapped with the PLA chains of MWNT‐g‐PLA. Copyright © 2008 John Wiley & Sons, Ltd.     

Effect of polystyrene-grafted multi-walled carbon nanotubes on the viscoelastic behavior and electrical properties of polypropylene-based nanocomposites

In this work, a free-radical grafting method was used to modify multi-walled carbon nanotubes (MWNT) to improve their dispersion in a polymer matrix by use of a compounding technique. By free-radical grafting for in-situ polymerization, MWNT agglomerates are turned into a networked micro-structure, which in turn builds up a strong interfacial interaction with the polymeric matrix during the mixing procedure. Polystyrene (PS)-MWNT with a hairy rod nanostructure were synthesized by in-situ free-radical polymerization of styrene monomer on the surface of MWNT. PS-MWNT/polypropylene (PP) nanocomposites were prepared by melt mixing. The effect of polystyrene-grafted multi-walled carbon nanotube (PS-MWNT) content on the rheological properties of the polypropylene (PP)-based nanocomposites was investigated. Surface characteristics of PS-MWNT were investigated by infrared spectroscopy, Raman spectroscopy (FT-Raman), thermogravimetric analysis, and transmission electron microscopy. The rheological properties of the PS-MWNT/PP composites were confirmed by rheometry. The complex viscosity of the PS-MWNT/polypropylene (PP) nanocomposites increased with increasing PS-MWNT content, primarily because of an increase in the storage modulus G??. In-situ-polymerized PS-MWNT were uniformly distributed in the PP matrix. In addition, the PS-MWNT were interconnected in the PP matrix and then formed PS-MWNT networks, resulting in the formation of a conducting network. Therefore, compared with samples with pristine MWNT, PS-MWNT-reinforced samples have lower conductivity as a resulting of PS grafting on the surface of MWNT.     

多壁碳纳米管/溴/聚苯乙炔三元复合材料导电性能的研究

通过机械共混和溶液共混制备了多壁碳纳米管(MWNTs)/溴/聚苯乙炔(PPA)三元复合材料, 复合材料表现出良好的导电性能, 电导率为10 S/m, 达到掺溴MWNTs的导电水平. 通过固体紫外光谱、XPS和SEM分析了复合材料中MWNTs、溴与PPA三者之间的相互作用, 研究了独立导电单元的形成, 以及导电单元对电导率提高所起的作用. 结果表明, 当MWNTs含量较低时, MWNTs和PPA之间的溴转移导致复合材料电导率降低; MWNTs含量较高时, 独立导电单元的数目增多, 复合材料的电导率随之大幅提高.     

多壁碳纳米管/溴/聚苯乙炔三元共混物导电性能的研究

通过机械共混和溶液共混制备了多壁碳纳米管(MWNTs)/溴/聚苯乙炔(PPA)三元复合材料,复合材料表现出良好的导电性能,电导率为10S/m,达到掺溴MWNTs的导电水平.通过固体紫外光谱、XPS和SEM分析了复合材料中MWNTs、溴与PPA三者之间的相互作用,研究了独立导电单元的形成,以及导电单元对电导率提高所起的作用.结果表明,当MWNTs含量较低时,MWNTs和PPA之间的溴转移导致复合材料电导率降低;MWNTs含量较高时,独立导电单元的数目增多,复合材料的电导率随之大幅提高.     

Influence of multiwall carbon nanotubes on morphology and electrical conductivity of PP/ABS blends

Polypropylene (PP) and acrylonitrile‐butadiene‐styrene (ABS) blends with multiwall carbon nanotubes (MWNT) were prepared by melt mixing. PP/ABS blends without MWNT revealed coarse co continuous structures on varying the ABS content from 40 to 70 wt %. Bulk electrical conductivity of the blends showed lower percolation threshold (0.4–0.5 wt %) in the 45/55 co continuous blends whereas the percolation threshold was between 2 and 3 wt % in matrix‐particle dispersed morphology of 80/20 blends. Interestingly, droplet size was observed to decrease with addition of MWNT above percolation threshold in 80/20 blends. Further, the bulk electrical conductivity was found to be dependent on the melt flow index of PP. The non‐polar or weakly polar nature of blends constituents resulted in the temperature independent dielectric constant, dielectric loss, and DC electrical conductivity. Rheological analysis revealed the formation of 3D network‐like structure in 80/20 PP/ABS blends at 3 wt % MWNT. An attempt was made to understand the relationship between rheology, morphology, and electrical conductivity of these blends. © 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 2286–2295, 2008     

Assembly of well-aligned multiwalled carbon nanotubes in confined polyacrylonitrile environments: electrospun composite nanofiber sheets

Highly oriented, large area continuous composite nanofiber sheets made from surface-oxidized multiwalled carbon nanotubes (MWNTs) and polyacrylonitrile (PAN) were successfully developed using electrospinning. The preferred orientation of surface-oxidized MWNTs along the fiber axis was determined with transmission electron microscopy and electron diffraction. The surface morphology and height profile of the composite nanofibers were also investigated using an atomic force microscope in tapping mode. For the first time, it was observed that the orientation of the carbon nanotubes within the nanofibers was much higher than that of the PAN polymer crystal matrix as detected by two-dimensional wide-angle X-ray diffraction experiments. This suggests that not only surface tension and jet elongation but also the slow relaxation of the carbon nanotubes in the nanofibers are determining factors in the orientation of carbon nanotubes. The extensive fine absorption structure detected via UV/vis spectroscopy indicated that charge-transfer complexes formed between the surface-oxidized nanotubes and negatively charged (-CN[triple bond]N:) functional groups in PAN during electrospinning, leading to a strong interfacial bonding between the nanotubes and surrounding polymer chains. As a result of the highly anisotropic orientation and the formation of complexes, the composite nanofiber sheets possessed enhanced electrical conductivity, mechanical properties, thermal deformation temperature, thermal stability, and dimensional stability. The electrical conductivity of the PAN/MWNT composite nanofibers containing 20 wt % nanotubes was enhanced to approximately 1 S/cm. The tensile modulus values of the compressed composite nanofiber sheets were improved significantly to 10.9 and 14.5 GPa along the fiber winding direction at the MWNT loading of 10 and 20 wt %, respectively. The thermal deformation temperature increased with increased MWNT loading. The thermal expansion coefficient of the composite nanofiber sheets was also reduced by more than an order of magnitude to 13 x 10(-6)/ degrees C along the axis of aligned nanofibers containing 20 wt % MWNTs.     

Synthesis and characterization of polyaniline‐multiwalled carbon nanotube nanocomposites in the presence of sodium dodecyl sulfate

Polyaniline‐carboxylic acid functionalized multi‐walled carbon nanotube (PAni/c‐MWNT) nanocomposites were prepared in sodium dodecyl sulfate (SDS) emulsion. First, the c‐MWNTs were dispersed in SDS emulsion then the aniline was polymerized by the addition of ammonium persulfate in the absence of any added acid. SDS forms the functionalized counterion in the resulting nanocomposites. The content of c‐MWNTs in the nanocomposites varied from 0 to 20 wt%. A uniform coating of PAni was observed on the c‐MWNTs by field‐emission scanning electron microscopy (FESEM). The PAni/c‐MWNT nanocomposites have been characterized by different spectroscopic methods such as UV‐Visible, FT‐Raman, and FT‐IR. The UV‐Visible spectra of the PAni/c‐MWNT nanocomposites exhibited an additional band at around 460 nm, which implies the induced doping of the MWNTs by the carboxyl group. The FT‐IR spectra of the PAni/c‐MWNT nanocomposites showed an inverse intensity ratio of the bands at 1562 and 1480 cm^?1 as compared to that of pure PAni, which reveals that the PAni in the nanocomposites is richer in quinoid units than the pure PAni. The increase in the thermal stability of conductivity of the nanocomposites was due to the network structure of nanotubes and the charge transfer between the quinoid rings of the PAni and the c‐MWNTs. Copyright © 2008 John Wiley & Sons, Ltd.     

Surface morphology and electrical properties of polyurethane nanofiber webs spray‐coated with carbon nanotubes

Multiwalled carbon nanotubes (MWNTs) were spray‐coated on electrospun polyurethane nanofiber webs for electrical conductive application. For the effective coating of MWNTs, hyperbranched polyurethane (HBPU) was used by blending with linear polyurethane, which was synthesized in the A₂ + B₃ approach using poly(ε‐caprolactone)diol, 4,4′‐methylene bis(phenylisocynate), and castor oil. SEM measurements showed that the MWNTs could be coated well along the surface of nanofibers when the HBPU was blended in the linear polyurethane nanofibers. Blending of HBPU in the nanofibers also affected the electrical conductivity of MWNT‐coated nanofiber webs. The low electrical resistance from 20 to 400 Ω/sq was obtained for MWNT‐coated nanofiber webs and their electrical resistance decreased with an increase of spraying frequency. As a potential application of MWNT‐coated nanofiber webs, the electrical heating effect because of applied voltage was demonstrated. Copyright © 2011 John Wiley & Sons, Ltd.     

Surface Modification of Carbon Nanotube by Poly(ethylene glycol) for the Preparation of Poly(vinyl alcohol) Nanocomposite

Herein, PEGylated multi-walled carbon nanotube (MWNT) was prepared for the successive fabrication of poly(vinyl alcohol) PVA/MWNT nanocomposite film by solution casting. The surface modified MWNT showed a good colloidal stability in a polar solvent, i.e., water. Also, the PEGylated MWNT had an improved dispersion stability in aqueous PVA solution. The mixture of PEGylated MWNT and PVA dissolved in water was film casted and the dispersion uniformity and corresponding improvement of electrical conductivity were investigated. The electrical conductivity of PVA/modified MWNT composite film was three-fold higher than that of PVA/pristine MWNT composite film due to the much improved distribution uniformity of modified MWNT in PVA matrix.     

Novel conductive nanocomposites from perfluoropolyether waterborne polyurethanes and carbon nanotubes

The exceptional electrical conductivity of carbon nanotubes (CNTs) has been exploited for the preparation of conductive nanocomposites based on a large variety of insulating polymers. Among these, perfluoropolyether‐polyurethanes (PFPE‐PUs) represent a class of highly performing fluorinated materials with excellent water/oil repellency, chemical resistance, and substrate adhesion. The incorporation of highly conductive fillers to this class of highly performing materials allows them to be exploited in new technological and industrial fields where their unique properties need to be combined with the electrical conductivity or the electrostatic dissipation properties of carbon nanotubes. However, no studies have been presented so far on nanocomposites based on PFPE‐PUs and CNTs. In this work, polymer nanocomposites based on waterborne PFPE‐PUs and increasing amounts of carboxylated multiwall CNTs (COOH‐CNTs) were prepared and characterized for the first time. The effect of increasing concentration of COOH‐CNTs on the physical, mechanical, and surface properties of the nanocomposites was investigated by means of rheological measurements, dynamic mechanical analysis, thermal characterization, optical contact angle measurements, and scanning electron microscopy. In addition, electrical measurements showed that the highly insulating undoped PFPE‐PU system undergoes substantial modifications upon addition of COOH‐CNTs, leading to the formation of conductive nanocomposites with electrical conductivities as high as 1 S/cm. The results of this study demonstrate that the addition of COOH‐CNTs to PFPE‐PU systems represents a promising strategy to expand their possible use to technological applications where chemical stability, water/oil repellence and electrical conductivity are simultaneously required. Copyright © 2014 John Wiley & Sons, Ltd.     

Comparative study on the properties of poly(trimethylene terephthalate) ‐based nanocomposites containing multi‐walled carbon (MWCNT) and tungsten disulfide (INT‐WS2) nanotubes

Multi‐walled carbon (MWCNT) and tungsten disulfide (INT‐WS₂) nanotubes are materials with excellent mechanical properties, high electrical and thermal conductivity. These special properties make them excellent candidates for high strength and electrically conductive polymer nanocomposite applications. In this work, the possibility of the improvement of mechanical, thermal and electrical properties of poly(trimethylene terephthalate) (PTT) by the introduction of MWCNT and INT‐WS₂ nanotubes was investigated. The PTT nanocomposites with low loading of nanotubes were prepared by in situ polymerization method. Analysis of the nanocomposites' morphology carried out by SEM and TEM has confirmed that well‐dispersed nanotubes in the PTT matrix were obtained at low loading (<0.5 wt%). Thermal and thermo‐oxidative stability of nanocomposites was not affected by the presence of nanotubes in PTT matrix. Loading with INT‐WS₂ up to 0.5 wt% was insufficient to ensure electrical conductivity of PTT nanocomposite films. In the case of nanocomposites filled with MWCNT, it was found that nanotube incorporation leads to increase of electrical conductivity of PTT films by 10 orders of magnitude, approaching a value of 10^?3 S/cm at loading of 0.3 wt%. Tensile properties of amorphous and semicrystalline (annealed samples) nanocomposites were affected by the presence of nanotubes. Moreover, the increase in the brittleness of semicrystalline nanocomposites with the increase in MWCNT loading was observed, while the nanocomposites filled with INT‐WS₂ were less brittle than neat PTT. Copyright © 2016 John Wiley & Sons, Ltd.     

磺化聚苯乙炔/多壁碳纳米管复合材料导电机理研究

将磺化聚苯乙炔(SPPA)与多壁碳纳米管(MWNT)超声共混制备得到SPPA/MWNT复合材料. 用四探针电阻率测试、场发射扫描电镜(FESEM)、XPS、UV-Vis、XRD等方法对复合材料导电机理进行研究. 结果表明, SPPA/MWNT的电导率发生两次突跃；掺杂剂MWNT具有低的临界阈值; 临界阈值附近, 复合材料中MWNT具有不连续分布的现象及复合材料电阻呈负温度系数(NTC)效应; SPPA/MWNT复合材料中MWNT的碳原子对SPPA 进行掺杂. 推测复合材料的导电机理为, 共轭聚合物SPPA不仅被导电粒子MWNT物理填充, 同时还被MWNT的碳原子掺杂, 使复合材料中存在两种导电通路而导电, 一是因被掺杂而成为高电导率主体的SPPA相互接触形成的导电通路, 二是MWNT相互接触形成的导电通路.     

多壁碳纳米管与溴的相互作用及导电机理

通过溴蒸气的吸附, 提高多壁碳纳米管(MWNT)的本征导电性能, 加溴多壁碳纳米管的电导率提高了3倍. X光电子能谱、近红外光谱、紫外光谱、拉曼光谱表明多壁碳纳米管与溴之间存在共轭作用, 这种作用导致多壁碳纳米管上的π电子向溴偏移, 产生空穴载流子. 利用半导体能带图, 提出加溴多壁碳纳米管微观体系模型来研究溴对多壁碳纳米管的作用及导电机理.     

Polyethylene thermal oxidative stabilisation in carbon nanotubes based nanocomposites

Multiwall carbon nanotubes (MWNT)/linear low density polyethylene (LLDPE) nanocomposites were studied in order to understand the stabilisation mechanism for their thermal and oxidative degradation. Thermogravimetry coupled with infrared evolved gas analysis and pyrolysis gas chromatography-mass spectrometry demonstrate that MWNT presence slightly delays thermal volatilisation (15-20 °C) without modification of thermal degradation mechanism. Whereas thermal oxidative degradation in air is delayed by about 100 °C independently from MWNT concentration in the range used here (0.5-3.0 wt.%). The stabilisation is due to formation of a thin protective film of MWNT/carbon char composite generated on the surface of the nanocomposites is shown by SEM and ATR FTIR of degradation residues. The film formation mechanism is discussed.     

Electroactive Shape‐Memory Polyurethane Composites Incorporating Carbon Nanotubes

Summary: Electro‐active shape‐memory composites were synthesized using conducting polyurethane (PU) composites and multi‐walled carbon nanotubes (MWNTs). Surface modification of the MWNTs (by acid treatment) improved the mechanical properties of the composites. The modulus and stress at 100% elongation increased with increasing surface‐modified MWNT content, while elongation at break decreased. MWNT surface modification also resulted in a decrease in the electrical conductivity of the composites, however, as the surface modified MWNT content increased the conductivity increased (an order of 10⁻³ S · cm⁻¹ was obtained in samples with 5 wt.‐% modified‐MWNT content). Electro‐active shape recovery was observed for the surface‐modified MWNT composites with an energy conversion efficiency of 10.4%. Hence, PU‐MWNT composites may prove promising candidates for use as smart actuators.

The electro‐active shape‐recovery behavior of PU‐MWNT composites. The pictured transition occurs within 10 s when a constant voltage of 40 V is applied.     

形状记忆聚偏氟乙烯/丙烯酸酯/碳纳米管纳米复合材料的导电及导热性能

利用聚偏氟乙烯（PVDF）微小结晶的物理交联点作用,制备了形状记忆性能优异的聚偏氟乙烯/丙烯酸酯聚合物（PVDF/ACM）共混材料,为提高其导电及导热性能,于其中引入了碳纳米管（CNT）,系统研究了PVDF/ACM/CNT三元体系纳米复合材料的导热及导电性能。 结果表明,碳纳米管在PVDF/ACM体系中分散均匀;在基本保持其形状记忆性能的前提下,碳纳米管的加入使材料导热性能及导电性能有较大程度的提高：质量分数为4%的CNT使材料25 ℃的电阻值降低至5000 Ω/square,导热系数提高至0.157 W/(m·K)。