Electrorheological properties of poly(acrylonitrile) microspheres coated with multiwall carbon nanotubes

Poly(acrylonitrile) (PAN) particles coated with functionalized multiwall carbon nanotubes (fMCNTs) were prepared and applied to electrorheological (ER) fluids. First, carboxylic acid groups were introduced on the multiwall carbon nanotubes by chemical oxidation method. Then, nitrile groups on the surface PAN particles were modified to amine groups by Co catalysis reaction. Finally, fMCNTs were anchored on the surface of polymer particles by covalent bonding between carboxylic acid groups on fMCNTs and amine groups on particles. fMCNTs attached polymeric microspheres were characterized by scanning electron microscopy and optical microscopy. The ER properties of fMCNTs modified microspheres were measured under controlled electric fields. Although the amount of fMCNTs anchored on the surfaces of microspheres was 1 wt.% of polymers, good ER properties were observed. This improvement may be caused by fMCNTs enhancing the electrical properties of polymer microspheres.     

Multi-walled carbon nanotubes fabricated by electrospinning of acrylonitrile/nylon solution and subsequent carbonization

The poly(acrylonitrile) (PAN) nanofiber web interpenetrated nylon-6 nanofiber supporters were prepared by electrospinning of an acrylonitrile (AN)/nylon-6 solution. It was realized that the average diameters of PAN and nylon-6 nanofiber were 20 and 100 nm, respectively, and that the PAN nanofibers constructed spider-mat networks which were supported by the robust nylon-6 nanofiber pillars. After stabilization and carbonization above 600 degrees C, both hollow-shaped and bamboo-shaped multi-walled carbon nanotubes (MWCNTs) were formed with the diameter range from 5 to 20 nm. The morphology and structure of MWCNTs had been further investigated by the combination techniques of transmission electron microscopy (TEM), electron diffraction (ED), X-ray diffraction (XRD) and elemental analyzer (EA).     

Preparation and characterization of electrospun core sheath nanofibers from multi-walled carbon nanotubes and poly(vinyl pyrrolidone)

Electrospinning is a versatile technique to prepare polymer fibers in nano to micrometer size ranges using very high electrostatic fields. Electrospun nanofibers with tunable porosity and high specific surface area have various applications, including chromatographic supports for protein separation, biomedical devices, tissue engineering and drug delivery matrices, and as key components in solar cells and supercapacitors. Unspinnable materials such as nanoparticles, nanorods, nanotubes or rigid conducting polymers can also be electrospun into fibers through co-axial electrospinning. In this study, we have prepared core-sheath nanofibers utilizing co-axial electrospinning. The core portion of these electrospun fibers consists of multi-walled carbon nanotubes and the sheath portion is poly(vinyl pyrrolidone) (PVP). Various morphologies were obtained by changing both core and sheath solution concentrations. The core-sheath nanofibers were characterized by scanning electron microscopy and transmission electron microscopy, to confirm core-sheath morphology, thermogravimetric analysis, and mechanical strength testing. The electrical conductivity of the surfaces of poly(vinyl pyrrolidone) fibers and poly(vinyl pyrrolidone)-multi-walled nanotube fibers were both 10(-15) S/m. The highest bulk conductivity observed for the poly(vinyl pyrrolidone)-multi-walled nanotube fibers was 1.2 x 10(-3) S/m.     

Surface characterization of poly(acrylonitrile) based intermediate modulus carbon fibres

The interface between the fibre and the matrix is a very important factor influencing the mechanical behaviour of composite materials. For superior composite performance, one must not only select optimal fibres and matrices, but also optimize the interface between them. However, the control of the interface properties is not an easy task. This work is an interdisciplinary and integrated approach to the problem. The effect of different degrees of a wet oxidative surface treatment on the surface of poly(acrylonitrile) based intermediate modulus carbon fibres (Courtaulds IM CG43–750) has been studied using classical thermodynamic as well as spectroscopic techniques, aimed at obtaining a complete physical and chemical characterization of the fibre surface. The results show that all aspects of the fibre surface are influenced by the surface treatments, which are specially designed to improve the adhesion between fibre and matrix. The study outlines the most important surface features improving this adhesion. The results concerning the characterization of the fibre surface contribute, when combined with micromechanical tests, to clarifying the adhesion mechanisms, revealing, at the same time, a mechanical interlocking and a chemical interaction.     

Study on morphology and characterization of poly(mphenylene isophtalamide)/multi-walled carbon nanotubes composite nanofibers by electrospinning

Electrospinning technique is the main method of preparing polymer nanofiber simply, directly and continuously at present. In this work, electrospinning blend solution was prepared by in-situ polymerization using acid-modified multi-walled carbon nanotubes (MWNTs), m-phenylenediamine (MPD) and isophthaloyl chloride (IPC). And then composite nanofibers were prepared by electrospinning. MWNTs played an important role in nanofiber's properties. The effects of MWNTs on the morphology and characterization of the MWNTs/PMIA composite nanofibers were investigated. Scanning electron microscopy (SEM), thermal gravimetric analyzer (TGA), and X-ray diffraction (XRD) were utilized to characterize the MWNTs/PMIA nanofibers morphology and properties. The experimental results indicated that the nanofibers diameter decreased and solution dynamic viscosity increased with increasing MWNTs contents. XRD data demonstrated that PMIA composite nanofibers had the same crystal type as the pure PMIA nanofiber, and crystallinity was improved with increasing MWNTs loading. Transmission electron microscopy (TEM) was used to confirm MWNTs aligned along the axis of composite nanofibers.     

Synthesis and characterization of poly(butylene oxide) grafted carbon nanofibers

The grafting of polybutylene oxide onto purified and functionalized carbon nanofibers is reported. Grafting was possible after the insertion of 2-(formyloxy)ethyl 2-bromo-2-methylpropanoate onto the carbon nanofibers. The polymerization of tetrahydrofuran was mediated by copper(I) bromide and 1,1,4,7-pentamethyl diethylenetriamine. The polymer-grafted carbon nanofibers were characterized by Raman spectrsocopy, Transmission Electron Microscopy, and Thermogravimetric Analysis. TEM images of CNF-COOH (A), CNF-PBO (B), completely open tip of CNF-COOH, and coated tip of CNF-PBO (D) are shown in the left panel. The right panel depicts the distribution of bromine (blue), and carbon (red) atoms inside and in the vicinity of CNF-Br (as obtained by Electron Energy Loss Spectroscopy). The bottom shows the actual doped CNF. Preliminary data showed that these modified fibers have potential applications as smart (electrorheological) fluids.     

Effect of carbonization temperature on properties of aligned electrospun polyacrylonitrile carbon nanofibers

Aligned electrospun nanofibrous bundle was used as the raw material for pretreatment, preoxidation and carbonization processes to prepare carbon nanofibers in a procedure temperature-controlled sintering furnace. Effect of carbonization temperature on the morphology and structural performance of nanofibers was investigated in present study. Results showed that R_I (the relative intensity radio between Disordered peak and Graphite peak) of nanofibers carbonized at 1000 °C is 0.90, carbon content is up to 85.67%, conductivity is 105.44 S·cm^− 1, Young's modulus is 68.8 ± 0.42 GPa, and fiber strength is 306.0 ± 9.0 MPa, all of which endow the fibers with a superior comprehensive property.     

Conducting nanocomposites of poly(N-vinylcarbazole) with single-walled carbon nanotubes

The in situ solid-state polymerization of N-vinylcarbazole (NVC) at an elevated temperature in the presence of single-walled carbon nanotubes (SWCNTs) leads to the formation of new types of composite materials, the morphology and properties of which were characterized by field-emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), Fourier transform infrared (FTIR) spectroscopy, X-ray photoelectron spectroscopy (XPS), thermogravimetric analysis (TGA), and electrical property measurements. FTIR spectroscopy and XPS studies confirmed the ability of SWCNTs to initiate the in situ polymerization of NVC monomers. FE-SEM and TEM results showed the coating of the outer surfaces of SWCNTs by the PNVC hompolymer with separation of individual SWCNTs from the bundles. Thermogravimetric analysis revealed a moderate improvement in the thermal stability of the nanocomposites at a higher temperature region relative to the base polymer. The electrical conductivity of neat polymer dramatically improved in the presence of SWCNTs. For example, dc electrical conductivity increased from 10(-16)-10(-12) S x cm(-1) for neat PNVC to approximately 10(-6) S x cm(-1) for nanocomposite containing 9 wt% SWCNTs.     

Assembly of fullerenol particles on carbon nanotubes through poly (acryloyl chloride)

Multiwalled carbon nanotubes (MWCNTs)/fullerenol composites were prepared through a facile method. Poly (acryloyl chloride) (PACl) was first grafted onto oxidized MWCNTs through the reaction between the acyl chloride groups of PACl with the hydroxyl groups on the surface of MWCNTs. The PACl with multiple acyl chloride groups provided more active points for further reactions. Subsequently, the remaining acyl chloride groups of PACl were allowed to react with the hydroxyl groups of fullerenols leading to the covalent attachment of the latter onto the grafted PACl chain. The MWCNTs/fullerenol composites thus obtained were characterized using Fourier transform infrared spectrometer (FTIR), transmission electron microscopy (TEM), and thermal gravimetric analysis (TGA).     

The poly(urethane-ionic liquid)/multi-walled carbon nanotubes composites

In the paper, a novel kind of imidazolium based poly(urethane-ionic liquid)/multi-walled carbon nanotubes (PUIL/MWCNT) composites was facilely prepared by uncovalent ways. The imidazolium based ionic liquid (IL) greatly improved the dispersion of pristine MWCNTs in PUIL by the π-cation interaction formed between the imidazolium cation and the π-electron of MWCNTs. The PUIL/MWCNT composites showed obviously increased modulus, glass transition temperature and tensile strength in comparison with PU/MWCNT composites. The thermal and mechanical properties of the PUIL/MWCNT composites presented significant increase with low load of the MWCNTs. It indicated the interactions between PUIL and MWCNTs played an important role to enhance the performances of the composites.     

Growth of multi-amine terminated poly(amidoamine) dendrimers on the surface of carbon nanotubes

An in situ repetitive divergent polymerization strategy was employed to grow multi-amine poly(amidoamine) dendritic macromolecules on the surfaces of multiwalled carbon nanotubes (MWNTs), affording novel three-dimensional (3D) molecular nanocomposites. The crude MWNTs were oxidized using H(2)SO(4)/HNO(3) = 3:1?(v/v) and then reacted with thionyl chloride, resulting in MWNTs functionalized with chlorocarbonyl groups (MWNT-COCl). MWNT-COCl, when reacted with an excess of ethylenediamine, produced amine-functionalized MWNT supported initiators (MWNT-NH(2)). Using the MWNT-NH(2) as the growth supporter and methylacrylate/ethylenediamine as building blocks, multi-amine dendritic poly(amidoamine) macromolecules were covalently grafted onto the sidewalls and ends of MWNTs via Michael addition reaction and amidation. Thermal gravimetric analysis (TGA) measurements showed that the weight ratio of the as-grown dendritic polymers on the MWNT surfaces lay in the 10%-50% range. The products were also characterized by Fourier transform infrared (FTIR), Raman, nuclear magnetic resonance (NMR), and transmission electron microscopy (TEM) analysis. The results indicate that the dendrimers are grafted onto the surface of MWNTs. The as-prepared nanocomposites exhibit excellent dispersibility in water.     

Vibration and buckling analysis of nanotubes (nanofibers) embedded in an elastic medium using Doublet Mechanics

In the present study, vibration and buckling of nanotubes (nanofibers) embedded in an elastic medium are studied. A length scale-dependent theory called Doublet Mechanics (DM) is used in the formulation. In this theory, discrete microstructure of solids is considered in the formulation and using a bottom-up approach macro level strains and stresses are obtained from microlevel strains and stresses. Taylor series expansion of the microlevel displacement is used in the definition of the micro strains. The number of terms in the Taylor series describes the microstructure of the considered solids. In this study, nanotube fibers are assumed as an Euler–Bernoulli beam embedded in an elastic medium. Simply supported and clamped boundary conditions are considered at the edges of the beams. Free vibration frequencies and critical buckling loads are obtained and compared with the classical elasticity results. It is shown that scale-dependent DM can be used at the nanolength scale.     

碳源对碳纳米管形态的影响

以苯和甲苯为碳源,二茂铁为催化剂,含硫化合物为助催化剂,采用浮游催化裂解法制备了碳纳米管,并采用TEM对不同条件下所得碳纳米管进行了形态分析。结果发现,碳源中苯和甲苯的配比对碳纳米管的形态有着重要的影响。以纯苯为碳源时,产物主要为直线型碳纳米管,并存在极少量短的弯曲型碳纳米管。随着碳源中甲苯比例的增加,产物中折线型碳纳米管增加。以纯甲苯为碳源,产物中仍有少量直线型碳纳米管,而不完全是折线型碳纳米管;此外,产物中还发现了极少量分支型碳纳米管。根据所得结果讨论分析了甲苯的加入对碳纳米管形态的影响以及各种碳纳米管的形成机理,认为可能是由于甲苯在催化热解过程中产生的碳种不同于苯催化热解所产生的碳种,造成碳在催化剂颗粒各处浓度不同,从而在碳纳米管的不同部位引入五元环和七元环而形成各种形态的碳纳米管。     

Estimation,using infrared spectroscopy,of the cyclization of poly(acrylonitrile) during the stabilization stage of carbon fibre production

This paper describes an FTIR method for quantifying the extent of conversion from PAN to oxidized (stabilized) PAN fibre in a series of partially-treated commercial samples. The conversion is quantified in terms of a conversion index. The results are considered in comparison with estimates obtained using WAXD and DSC measurements, and also with respect to changes in tensile strength of the samples. It is concluded that WAXD underestimates the degree of conversion in the initial stages of oxidation, and that DSC overestimates it near the end of the process. In contrast, the FTIR method is capable of giving a good indication of the conversion throughout the entire treatment period. The strength decreases monotonically through the series of samples, and correlates well with values of the conversion index as determined from FTIR.     

Controlled lowering of graphitization temperature of electrospun poly(acrylonitrile) based carbon fiber by carbon nanotube embedment

Structural evolution of electrospun poly(acrylonitrile) based carbon fibers embedded with multi-wall carbon nanotube (MWCNT) by heat treatment between 1000 and 3000 °C is reported. The graphitization of the fibers is seen to be enhanced in the presence of MWCNT. Graphite fibers with high crystallinity and with a lattice constant nearly equal to that of highly oriented pyrolytic graphite can be prepared at a temperature of 2000 °C, with a small percentage (∼ 5 wt.%) of MWCNT embedded into it. This is a reduction of the graphitization temperature by ∼ 1000 °C from the conventional graphitization temperature of ∼ 3000 °C without the addition of any metallic catalyst.     

SDBS修饰碳纳米管及其增强聚乳酸复合材料的制备与表征

采用十二烷基苯磺酸钠(SDBS)对碳纳米管进行表面修饰,并以其为增强体,利用溶剂蒸发法制备了碳纳米管/聚乳酸复合材料.采用红外吸收光谱、偏光显微镜、扫描电镜及拉伸实验研究了SDBS修饰的碳纳米管表面形貌和结构以及碳纳米管/聚乳酸复合材料的链结构、聚集态结构和力学性能.SDBS修饰可使碳纳米管均匀分散于有机溶剂中,并改善...     

De novo growth of poly(amidoamine) dendrimers on the surface of multi-walled carbon nanotubes

Carbon nanotubes (CNTs) are often used after modification. Poly(amidoamine) (PAMAM) dendrimers modified CNTs have attracted attentions due to their rich terminal amino groups. However, direct grafting of PAMAM dendrimers on CNTs’ surface is limited by the steric hindrance and its supply. De novo growth of PAMAM on multi-walled carbon nanotubes (MWCNTs), i.e., PAMAM@CNTs, is expected to eliminate the limits since the adopted reagents are readily available small molecular chemicals. It was realized using a divergent method and a “grafting from” technique by alternate amidization of terminal ester groups with ethylenediamine and Michael addition of methyl acrylate to the yielding amino groups. Spectral analysis, including Fourier transform infrared, Raman, hydrogen nuclear magnetic resonance, and X-ray photo-electron spectroscopy, verified that the functional groups were covalently grafted on the surface of MWCNTs, while thermogravimetric and elemental analysis showed that these groups were exponentially grown on MWCNTs, suggesting the formation of a dendritic PAMAM. Besides, high resolution transmission electron microscopy also confirmed that the spherical PAMAM was formed on the CNTs’ surface and an average particle size of 15–20 nm for G8.0-dendrimers was obtained.