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。     

聚乳酸/石墨/多壁碳纳米管复合材料的制备及性能

通过共溶剂法制备了由石墨(GN)和多壁碳纳米管(MWCNTs)掺杂的聚乳酸(PLA)纳米复合材料,借助扫描电镜等手段,研究了MWCNTs用量对复合材料微观结构、热稳定性、导热和导热性能及介电性能的影响。结果显示,MWC-NTs和GN在PLA基体中形成了稳定的导电和导热网络结构,从而导致复合材料具有较低的导电和导热逾渗阈值,其值约为MWCNTs/GN=0.5/1。MWCNTs和GN均匀分散和协同增强效应促使复合材料热稳定性、导热和导电性能明显提高。与纯PLA相比,填料在逾渗阈值附近的复合材料的初始分解温度提高了近16℃,导热系数提高了1倍,体积电阻降低了109数量级。     

酸化处理多壁碳纳米管/氰酸酯树脂复合材料性能

采用酸化处理的多壁碳纳米管（MWCNTs）增强双酚A型氰酸酯-酚醛型氰酸酯（BCE-NCE）树脂。通过SEM、TEM对MWCNTs/BCE-NCE树脂复合材料微观结构进行表征,利用DSC、DMA和TG/DTA对MWCNTs/BCE-NCE树脂复合材料热性能进行研究,采用电子拉力机对MWCNTs/BCE-NCE树脂复合材料力学性能进行测试,采用谐振腔法对MWCNTs/BCE-NCE树脂复合材料介电性能进行测试。结果表明,混酸处理过的MWCNTs在BCE-NCE树脂基体中的分散效果较好。MWCNTs对BCE-NCE树脂热力学性能影响不大,当MWCNTs添加量为0.8wt%时,BCE-NCE树脂玻璃化转变温度（T_g）从298℃下降到285℃,但仍维持较高水平。当MWCNTs添加量为0.6wt%时,MWCNTs/BCE-NCE树脂复合材料冲击强度为11.40 kJ/m²,提高了40.7%。MWCNTs的加入增加了BCE-NCE树脂介电常数和介电损耗,当MWCNTs添加量为0.8wt%、频率为1 GHz时,MWCNTs/BCE-NCE树脂复合材料介电常数为5.1,介电损耗为0.032。因此,MWCNTs/BCE-NCE树脂复合材料未来可在耐高温复合材料和电子等行业应用。     

原位聚合制备尼龙6/多壁碳纳米管复合材料及性能表征

用原位聚合法制备了尼龙6/多壁碳纳米管(MWCNTs)复合材料。先对多壁碳纳米管进行胺基功能化处理,再研究了多壁碳纳米管添加量对复合材料电性能和力学性能的影响,结果显示,复合材料体积电阻率和表面电阻率相对于不加碳纳米管制得的尼龙6基体降低了3个数量级,复合材料的介电常数显著增加,相对于不加碳纳米管的增加了71%;复合材料的弹性模量、弯曲模量、弯曲强度随碳纳米管加入量的增加大幅提高。     

Preparation and characterization of hydroxyl (–OH) functionalized multi-walled carbon nanotube (MWCNT)–Dowtherm A nanofluids

In the present work, the thermal conductivity and viscosity of hydroxyl (–OH) functionalized multi-walled carbon nanotubes (MWCNTs)–Dowtherm A (eutectic mixture of biphenyl (C₁₂H₁₀) and diphenyl oxide (C₁₂H₁₀O)) nanofluids are discussed. As-received hydroxyl (–OH) functionalized MWCNTs are characterized using x-ray diffraction (XRD), FT-Raman spectroscopy, Fourier transform infrared spectroscopy (FTIR), transmission electron microscopy (TEM), and thermogravimetry, differential thermogravimetry, and differential scanning calorimetry (TGA-DTG/DSC) analysis. Hydroxyl (–OH) functionalized MWCNT–Dowtherm A nanofluids are prepared in different concentrations (0.001–0.005?g) of MWCNT and characterized at various temperatures (303–323?K). The thermal conductivity of hydroxyl (–OH) functionalized MWCNT–Dowtherm A nanofluids increases with the concentration of carbon nanotubes as well as with temperature. The possible mechanism for the enhancement observed may be ascribed to the percolation of heat through the nanotubes to form a tri-dimensional network. Also, as the temperature increases, the viscosity of the nanofluid decreases, which results in an increase in Brownian motion of nanoparticles, this sets convection-like effects resulting in enhanced thermal conductivity.     

A comparative study on the electrical,thermal and mechanical properties of ethylene–octene copolymer based composites with carbon fillers

Conducting polymer composites (CPC) were prepared with an ethylene–octene copolymer (EOC) matrix and with either carbon fibers (CFs) or multiwall carbon nanotubes (MWCNTs) as fillers. Their electrical and thermal conductivities, mechanical properties and thermal stabilities were evaluated and compared. CF/EOC composites showed percolation behavior at a lower filler level (5 wt.%) than the MWCNT/EOC composites (10 wt.%) did. Alternating current (AC) conductivity and real part of permittivity (dielectric constant) of these composites were found to be frequency-dependent. Dimensions and electrical conductivities of individual fillers have a great influence on the conductivities of the composites. CF/EOC composites possessed higher conductivity than the MWCNT-composites at all concentrations, due to the higher length and diameter of the CF filler. Both electrical and thermal conductivities were observed to increase with increasing filler level. Tensile moduli and thermal stabilities of both (CF/EOC and MWCNT/EOC) composites increase with rising filler content. Improvements in conductivities and mechanical properties were achieved without any significant increase in the hardness of the composites; therefore, they can be potentially used in pressure/strain sensors. Thermoelectric behavior of the composites was also studied. Accordingly, CF and MWCNT fillers are versatile and playing also other roles in their composites than just being conducting fillers.     

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.     

Large dielectric constant of the chemically purified carbon nanotube/polymer composites

The chemically purified multiwalled carbon nanotube/poly(vinylidene fluoride) (MWCNT/PVDF) composites were fabricated. Raman spectroscopy and transmission electron microscopy micrographs indicated that the catalysts metal particles and amorphous carbon had been removed from the purified MWCNTs. The percolation threshold of the composites is relatively large, about 3.8 vol.%. The most important result is that the dielectric constant of the composites is enhanced remarkably, and the dielectric constant of 3600 is obtained in the composite with 8 vol.% purified MWCNT at 1 kHz. The large dielectric constant can be attributed to the preparation procedure and the interface effect between the MWCNTs and the polymer.     

Dielectric and mechanical properties of three-component Al2O3/MWCNTs/polyarylene ether nitrile micro-nanocomposite

Polyarylene ether nitrile (PEN)/multi-walled carbon nanotubes (MWCNTs)/alumina (Al₂O₃) micro-nanocomposite material films were fabricated by uncomplicated and accessible method, overcoming the difficulty of bad interaction between MWCNTs and PEN matrix. Scanning electron microscope revealed that MWCNTs were isolated by Al₂O₃ and realized better dispersion in matrix. Al₂O₃ particles hindered conductive MWCNTs from bridging with each other, working as dielectric obstacle. In addition, the micro-nanocomposite has excellent thermal stability and possesses high performance in dielectric and mechanical. The investigation results showed that the dielectric constant increased to 100.8 (50 Hz), which is 20 times higher than that of pure PEN while the dielectric loss was only 0.1 with 7 wt% MWCNTs loading. Meanwhile, the mechanical property indicated that the composite with 7 wt% MWCNTs loading reached their highest values. In other words, the composite with 7 wt% MWCNTs loading possess excellent mechanical property simultaneously as it reached the percolation threshold.     

The effects of the variations of carbon nanotubes on the micro-tribological behavior of carbon nanotubes/bismaleimide nanocomposite

Two kinds of original multiwalled carbon nanotubes (MWCNTs) with different diameters, and one carboxyliated MWCNTs were used to prepare three kinds of MWCNTs/bismaleimide (BMI) nanocomposites. The effects of the diameter, concentration and functional group of MWCNTs used in the composites on the micro-tribological behavior of the MWCNTs/BMI nanocomposites were investigated in this paper. The microhardness, the morphology of the worn surface, the glass transition temperature and dynamic mechanical properties of the MWCNTs/BMI nanocomposites were also measured to figure out the possible main wear mechanism of the composites. Results show that the addition of MWCNTs in BMI resin decreases the friction coefficient of the resin no matter what kind of MWCNTs is added. Moreover, the wear loss rate of all nanocomposites considerably decreases with the increasing of nanotube content until the content reaches 2.5 wt%. Functionalization of MWCNTs changes the main wear mechanism of the MWCNTs/BMI composite from adhesive wear (for pure BMI resin) to abrasive attrition by changing the self-lubricating property of the wore surface, the dispersion of MWCNTs in the BMI matrix, the interfacial strength between MWCNTs and the matrix as well as the internal strength of the materials.     

Enhanced dielectric and ferroelectric properties induced by TiO2@MWCNTs nanoparticles in flexible poly(vinylidene fluoride) composites

Flexible polymer based composites containing multi-walled carbon nanotubes (MWCNTs) have been reported to present high dielectric constant. However, the composites generally exhibit high dielectric loss and low dielectric breakdown strength, which prohibits their practical use in electronic and electric industry. MWCNTs were coated with a continuous layer of TiO₂ nanoparticles (TiO₂@MWCNTs) by a simple hydrothermal process and TiO₂@MWCNTs/poly(vinylidene fluoride) (PVDF) composites were prepared by a solution casting method. Compared to the pristine MWCNTs/PVDF composites, the TiO₂@MWCNTs/PVDF composites presented enhanced dielectric constant and lower dielectric loss. Additionally, the breakdown strength of the TiO₂@MWCNTs/PVDF composites was also improved, which is favorable for enhanced ferroelectric properties in the composites.     

Effect of solid lubricant silicone powder on the fluidity and properties of polyarylene ether nitrile nanocomposite

Improving the processing performance of polymers is an eternal topic in the polymer field. As a processing aid, solid lubricants improve the shortcomings of liquid lubricants that are easy to migrate. In this work, silicone powder was introduced into polyarylene ether nitrile (PEN)/multi-walled carbon nanotubes (MWCNTs) composites as a solid lubricant to improve the flowability and processability. Firstly, the effects of silicone powder and MWCNTs on the mechanical properties, thermal properties, dielectric properties and rheological properties of the composites were investigated. The experimental results show that the fluidity of the composites is improved obviously by adding silicone powder. In addition, a comparative experiment was carried out. Compared with PEN/MWCNTs composites, PEN/silicone powder/MWCNTs composites have better processing properties and dielectric properties. The complex viscosity is 308.1 at 10² Hz and the dielectric constant is 1?×?10⁵ at 10³ Hz. Therefore, silicone powder is of great research value as a solid lubricant in the field of polymer-based functional materials.

     

Influence of ultrasonic dual mixing on thermal and tensile properties of MWCNTs-epoxy composite

Multiwalled carbon nanotubes (MWCNTs) reinforced epoxy based composites were fabricated by using an innovative ultrasonic dual mixing (UDM) process consists of ultrasonic mixing with simultaneous magnetic stirring. The effect of addition of varying amount of MWCNTs on thermal stability and tensile properties of the epoxy based composite has been investigated. It is found that the thermal stability, tensile strength and toughness of the epoxy base improves with the increase of MWCNTs addition up to 1.5 wt.% and UDM processing at certain capacity of the system. Tensile tests and thermal gravimetric analysis (TGA) were performed on each group of composites containing different amount of MWCNTs to determine their mechanical and thermal properties respectively. The dispersion of 1.5 wt.% MWCNTs fillers in epoxy nanocomposites was studied by transmission electron microscopy (TEM) as well as by field emission scanning electron microscopy (FESEM) applied on their tensile fracture surface.     

Thermal conductivities of alumina-based multiwall carbon nanotube ceramic composites

Composites incorporating various vol.% (0.0, 1.1, 6.4, and 10.4) of multiwall carbon nanotubes (MWCNTs) in alumina were consolidated by the spark plasma sintering. Their thermal transport properties were investigated over the temperature range 300–800 K as a function of nanotube contents. It was observed that the temperature-dependent effective thermal conductivity decreases with the addition of MWCNTs in alumina. This behavior was analyzed in terms of phonon mean free path, elastic modulus, average sound speed, and interface thermal resistance. Compared with 1/T behavior for pristine alumina, a subtle decrease in temperature dependence of the thermal conductivity of the composites with the addition of MWCNTs is observed, indicating the presence of extra phonon scattering mechanism beyond the intrinsic phonon–phonon scattering. Simulation of experimental results with theoretical model shows that the large interfacial thermal barrier between MWCNTs and alumina plays a dominant role in controlling thermal transport properties of the composites. In addition to dominant interface thermal resistance other secondary factors such as nanotube agglomeration, processing defects, porosity also contribute for low thermal conductivity at the higher volume fraction of MWCNTs in the composite.     

MWCNTs改善WS2/三元乙丙橡胶复合材料的非线性电导特性与热导性能

通过在一定量的纳米WS₂中添加极少量的多壁碳纳米管（MWCNTs）,形成MWCNTs-WS₂复配填料,采用双辊开炼机将三元乙丙橡胶（EPDM）与不同配比的复配填料混合制备了不同MWCNTs含量的MWCNTs-WS₂/EPDM复合材料。并研究了极少量的MWCNTs添加对MWCNTs-WS₂/EPDM复合材料非线性电导性能、直流击穿性能和导热性能的影响。结果表明,极少量的MWCNTs对MWCNTs-WS₂/EPDM复合材料在25℃时的非线性电导特性起到明显的增强作用,且随着MWCNTs含量的增加,复合材料非线性电导特征有明显的规律性变化;由于MWCNTs自身的高电导率和电导正温度系数效应,MWCNTs-WS₂/EPDM复合材料电导率随电场强度的变化趋势在80℃时不再表现非线性特征。另外,极少量的MWCNTs对MWCNTs-WS₂/EPDM复合材料的热导率有明显地改善。      

Preparation of high k expanded graphite/CaCuTi4O12/cyanate ester composites with low dielectric loss through controlling the interfacial action between conductors and ceramics

New composites with high dielectric constant and low dielectric loss, based on expanded graphite (EG), CaCuTi₄O₁₂ (sCCTO) and cyanate ester (CE) resin, were developed by controlling the interaction between EG and sCCTO. Difference from EG, surface modified EG (mEG) has an additional strong chemical interaction with sCCTO, this not only improves the dispersion of fillers, but also enhances the filler-matrix interfacial adhesion, leading to different micro-structures and dielectric properties. Specifically, the percolation thresholds of mEG/sCCTO/CE and EG/sCCTO/CE composites are 3.45 vol% and 2.86 vol%, respectively. When the loading of conductors approaches the percolation threshold, mEG/sCCTO/CE composite has much higher dielectric constant and lower dielectric loss than EG/sCCTO/CE composite. The nature behind these attractive data was revealed by building an equivalent circuit.     

Free-volume correlation with mechanical and dielectric properties of natural rubber/multi walled carbon nanotubes composites

The microstructure, mechanical strength, dielectric properties, Doppler broadening measurements and positron life time studies of the composites containing multi walled carbon nanotubes (MWCNTs) and natural rubber (NR) are investigated. The uniform distribution of MWCNTs in the elastomer medium is studied by Raman spectroscopy and the electron microscopy images show the composite’s internal microstructure. Free volume sizes and interstitial mesopore sizes of the nanocomposites are determined by positron annihilation lifetime spectroscopy (PALS). PALS investigates the influence of the nanotubes in regulating the interphase nanoscale character. Strong interfacial interaction causes an apparent reduction of the free-volume fraction of NR probably by depressing the formation of free-volume holes in the interfacial region. The mechanical percolation and percolation observed from the dielectric measurements are correlated with the life time values. It is established that the sub-nano level free volumes and nano level structure of the composites have significant roles in regulating the mechanical properties.     

Structure–property relationships in isotactic polypropylene/multi-walled carbon nanotubes nanocomposites

In this work, the influence of multi-walled carbon nanotubes (MWCNT) on electrical, thermal and mechanical properties of CNT reinforced isotactic polypropylene (iPP) nanocomposites is studied. The composites were obtained by diluting a masterbatch of 20 wt.% MWCNT with a low viscous iPP, using melt mixing. The morphology of the prepared samples was examined through SEM, Raman and XRD measurements. The effect of MWCNT addition on the thermal transitions of the iPP was investigated by differential scanning calorimetry (DSC) measurements. Significant changes are reported in the crystallization behavior of the matrix on addition of carbon nanotubes: increase of the degree of crystallinity, as well as appearance of a new crystallization peak (owing to trans-crystallinity). Dynamic mechanical analysis (DMA) studies revealed an enhancement of the storage modulus, in the glassy state, up to 86%. Furthermore, broadband dielectric relaxation spectroscopy (DRS) was employed to study the electrical and dielectric properties of the nanocomposites. The electrical percolation threshold was calculated 0.6–0.7 vol.% MWCNT from both dc conductivity and dielectric constant values. This value is lower than previous mentioned ones in literature in similar systems. In conclusion, this works provides a simple and quick way for the preparation of PP/MWCNT nanocomposites with low electrical percolation threshold and significantly enhanced mechanical properties.     

Preparation,characterization and properties of polycaprolactone diol-functionalized multi-walled carbon nanotube/thermoplastic polyurethane composite

Multi-walled carbon nanotubes (MWCNTs) were chemically functionalized to prepare thermoplastic polyurethane (PU) composites with enhanced properties. In order to achieve a high compatibility of functionalized MWCNTs with the PU matrix, polycaprolactone diol (PCL), as one of PU’s monomers, was selectively grafted on the surface of MWCNTs (MWCNT–PCL), while carboxylic acid groups functionalized MWCNTs (MWCNT–COOH) and raw MWCNTs served as control. Both MWCNT–COOH and MWCNT–PCL improved the dispersion of MWCNTs in the PU matrix and interfacial bonding between them at 1 wt% loading fraction. The MWCNT–PCL/PU composite showed the greatest extent of improvement, where the tensile strength and modulus were 51.2% and 33.5% higher than those of pure PU respectively, without sacrificing the elongation at break. The considerable improvement in both mechanical properties and thermal stability of MWCNT–PCL/PU composite should result from the homogeneous dispersion of MWCNT–PCL in the PU matrix and strong interfacial bonding between them.     

聚丙烯腈基碳纳米管复合材料的制备及其表征

碳纳米管添加到聚合物中对其结构和性能都有深远的影响,本文通过浓硝酸对碳纳米管改性后,采用水相沉淀聚合的方法制备了聚丙烯腈/碳纳米管复合材料,同时研究了碳纳米管经过浓硝酸处理后其化学结构的变化;探讨了碳纳米管对聚丙烯腈复合材料热学和结晶性的影响。研究表明,浓硝酸常温处理不仅能除去杂质,还可以在碳纳米管表面引入羧基等含氧基团;加入碳纳米管后,聚丙烯腈的预氧化温度有一定程度的提前,放热量明显降低,同时对聚合物的结晶度也有一定程度的影响。