Evaluating the orientation and dispersion of carbon nanotubes inside nanocomposites by a focused-ion-beam technique

Poly ether ether ketone (PEEK)/multi-walled carbon nanotubes (MWNTs) nanocomposites were fabricated to characterize and understand the orientation and dispersion of carbon nanotubes (CNTs) in a polymer matrix. A focused-ion-beam (FIB) technique was used for milling the nanocomposite by a focused gallium ion beam, and the MWNTs were carefully observed. The PEEK preferentially disappeared when the Ga⁺ ion beam milled the composite, and MWNTs were exposed on the surface of composites. Using this method, it is very easy to estimate and directly evaluate the orientation of the MWNTs in the polymer matrix even though they are embedded in the polymer matrix. Transmission electron microscopy (TEM) was employed to characterize the detailed position of the nanotubes in the PEEK matrix.     

Preparation and properties of the polyimide/multi-walled carbon nanotubes (MWNTs) nanocomposites

The polyimide/multi-walled carbon nanotubes (MWNTs) nanocomposite films were prepared by mixing of poly(amic acid) (PAA) solution and MWNTs/DMAc suspension follow by mixture casting, evaporation and thermal imidization. To increase the chemical compatibility between polyimide matrix and MWNTs, MWNTs were modified with mixed strong acid. The results show that the dispersion of the MWNTs is improved greatly in the polyimide matrix after acid modification. The modified MWNTs are dispersed homogeneously in the polyimide matrix while the structure of the polyimide and MWNTs structures is stable in the preparation process. With the incorporation of MWNTs, the mechanical properties of the resultant nanocomposite films were greatly improved due to the strong interfacial interaction between the modified MWNTs and the polyimide matrix. The thermal stability of the nanocomposites was lower a little than pure polyimide because of the drop of thermostability of MWNTs through acid-treatment. The electrical conductivity and the dielectric constant of the nanocomposites were also having sharp increase, which is favorable for practical use in anti-static materials and embedded capacitors.     

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.     

Thermal conductivity of polymer composites with close-packed structure of nano and micro fillers

Thermal conductivity of polymer composites with nano and micro fillers has been investigated numerically and experimentally. The nano fillers used were multi-walled carbon nanotubes (MWNTs) and alumina nanoparticles, and the spherical alumina particles were selected as the micro fillers. A periodic unit cell with a random close-packed structure was created using a packing algorithm that treat the micro filler as spheres. Finite element analyses were also performed to predict the potential of nano fillers to enhance thermal conductivity of the composites and to analyze the effect of microstructure of micro fillers. Additionally, the polymer composites with nano and micro fillers were made and the thermal conductivity of the composites were measured. The results showed that the addition of MWNTs to the matrix lead to a large increase in thermal conductivity of the composites. The proposed thermal model predicted a thermal conductivity in good agreement with experiment.     

Synthesis and characteristics of multi-walled carbon nanotubes-polyimide nanocomposite films

The polyimide/multi-walled carbon nanotubes (PI/MWNTs) nanocomposite film has been successfully synthesized in this study. The source of MWNTs is prepared by chemical vapor deposition (CVD) method. Then the MWNTs are washed with acid for purification before being added into the polymer matrix. The acid-modified procedure aids in dispersing MWNTs in N,N-dimethylacetamide (DMAc) solvent. Based on the results of field emission scanning electron microscopy (FESEM) and transmission electron microscopy (TEM), the MWNTs are embedded in PI and well-dispersed within the PI matrix. The dynamic mechanical analysis (DMA) shows that the storage modulus of nanocomposite film is increased by 68% with the addition of 1 wt% MWNTs into PI. The nanocomposite films start to decompose at or above 400 degrees C and lose 5% of its weight at 545 degrees C according to thermogravimetric analysis (TGA). Meanwhile, the electrical conductivity of the nanocomposite film with 3 wt% MWNTs, is raised more than 10 orders of magnitude from 10(-15) to 10(-5) S/cm.     

Preparation and characterization of soluble and DBSA doped polyaniline grafted multi-walled carbon nanotubes nano-composite

Soluble and highly doped polyaniline (PANI) grafted multi-walled carbon nanotubes (MWNTs) nano-composite was synthesized by in situ oxidation polymerization, de-doping with ammonium hydroxide and doping the PANI-Emeraldine base (PANI-EB) grafted MWNTs nano-composite in N-methyl-2-pyrrolidinone (NMP) with Dodecyl benzene sulfonic acid (DBSA). Transmission electron microscope (TEM), Raman spectra, Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS) and standard four-probe methods were employed to characterize morphology, chemical structure and electronic conductivity of the nano-composite. The results show that oxidized phenylamine groups of phenylamine groups contained MWNTs (p-MWNTs) initiate PANI polymerization on the surface of p-MWNTs. PANI coatings graft on the surface of p-MWNTs via amide bond forming homogeneous core (p-MWNTs)–shell (PANI) nano-structures. After doping PANI-EB grafted MWNTs nano-composite with DBSA, the attachment of soluble DBSA doped PANI chains on the surface of p-MWNTs via covalent bonding renders p-MWNTs compatible with polymer matrix and lead to DBSA doped PANI grafted MWNTs nano-composite soluble and stable in NMP. Owing to incorporation of p-MWNTs and chemical bridges between p-MWNTs and PANI chains, conductivity of DBSA doped PANI grafted MWNTs nano-composite at room temperature is increased by about two orders of magnitude over neat DBSA doped PANI.     

Mechanical strength improvement of polypropylene threads modified by PVA/CNT composite coatings

Poly (vinyl alcohol)/carbon nanotube (PVA/CNT) composite was coated on the surface of polypropylene thread for toughness enhancement. Multiwall carbon nanotubes (MWNTs) were treated in acid and alkali to get water-soluble nanotubes, and then embedded into poly (vinyl alcohol) (PVA) matrix, resulting in polymer-carbon composite with homogeneous nanotube dispersion. The stress-strain measurements show that the tensile strength and toughness of the PVA/CNT coated thread increased by 117% and 560%, respectively. These results are supportive of good interfacial bonding between the carbon nanotubes (CNTs) and polymer matrix.     

Effect of Multi-Wall Carbon Nanotubes on the Mechanical Properties of Natural Rubber

Multi-walled carbon nanotubes (MWNTs) were used to prepare natural rubber (NR) nanocomposites. Our first efforts to achieve nanostructures in MWNTs/NR nanocomposites were formed by incorporating carbon nanotubes in a polymer solution and subsequently evaporating the solvent. Using this technique, nanotubes can be dispersed homogeneously in the NR matrix in an attempt to increase the mechanical properties of these nanocomposites. The properties of the nanocomposites such as tensile strength, tensile modulus, elongation at break and hardness were studied. Mechanical test results show an increase in the initial modulus for up to 12 times in relation to pure NR. In addition to mechanical testing, the dispersion state of the MWNTs into NR studied by Transmission Electron Microscopy (TEM) in order to understand the morphology of the resulting system     

多壁碳纳米管表面等离子体有机聚合改性

采用等离子体聚合技术在多壁碳纳米管(MWNTs) 表面聚合苯乙烯( Styrene) 、吡咯( Pyrrole) 有机膜。高分辨电镜( HRTEM) 分析显示MWNTs 内外表面均生成纳米级厚度的有机膜, 其中外壁表面厚约7 nm , 内壁表面厚约1～3 nm。将经过表面有机膜处理的MWNTs 添加到聚苯乙烯中, 制备出多壁碳纳米管/ 聚苯乙烯(MWNTs/ PS) 复合材料。扫描电镜(SEM) 对MWNTs/ PS 复合材料分析表明, 覆膜的MWNT 在复合材料中的分散得到改善。通过力学拉伸试验测试了MWNTs/ PS 复合材料断裂强度和弹性模量与MWNTs 含量的关系, 证明了经有机覆膜处理的MWNTs 与PS 形成的复合材料的整体强度得到显著提高。      

Study on dispersion and electrical property of multi-walled carbon nanotubes/low-density polyethylene nanocomposites

Sonication is one of the promising approaches to disperse nanoparticles into the base material thoroughly. Furthermore, coupling treatments for MWNTs and polymer matrix also contribute to homogenous dispersion of MWNTs among polymer matrix. In this paper, MWNTs and KH-550 were dispersed with acetone via sonication method, then, the MWNTs/low density polyethylene (LDPE) composites was prepared by using melt blending process. Effects of MWNTs and LDPE coupling treatment on dispersion and electrical property of the MWNTs/LDPE nanocomposites were investigated. SEM observation on fracture surfaces of the nanocomposites explained the functions of sonication and coupling treatment on the dispersion, and electrical conductivity of the nanocomposites was measured by four-contact scheme. The results displayed that the optimum sonication temperature was 70 °C and the optimum sonication amount of MWNTs particles in 200 ml KH-550 acetone solution was 20 g. Moreover, dispersion of the nanocomposites was improved with increasing sonication power amplitude. Furthermore, dispersion and electrical conductivity of the nanocomposites with coupling treatment LDPE were better than those of the nanocomposites with uncoupling treatment LDPE. The good dispersion and electrical conductivity enhancement are based on the strong bonding and coupling reaction of MWNTs and LDPE matrix, which associated greatly with sonication and coupling treatment.     

MWNTs/PU复合超细纤维的热性能及导电性能

采用静电纺丝技术制备了多壁碳纳米管/聚氨酯(MWNTs/ PU)复合超细纤维,并收集成无纺布薄膜,采用热失重分析仪(TGA)和动态力学分析仪(DMA)分析了纤维的热稳定性。利用数字高阻计(PC68)和LorestaGP电阻计测量了纤维薄膜的直流电导率随MWNTs含量的变化关系。为了研究该多孔薄膜的动态电学性能,同时采用Agilent 4294A阻抗分析仪测试了纤维薄膜的电导率在40 Hz～110 MHz频率范围内的变化关系,并与浇注试样的结果进行比较。结果表明,随MWNTs 在 PU 纤维中含量的增加,复合纤维的热稳定性提高。当10MWNTs质量分数达40 %时,PU的电导率提高近10 倍。     

Investigation of the electrical conductivity of HDPE composites filled with bundle-like MWNTs

Bundle-like multi-walled carbon nanotubes (MWNTs) were melting-mixed with high-density polyethylene (HDPE). MWNTs are distributed in the matrix mostly isolated. Agglomerates are observed at higher concentrations. The electric conductivity of the composites follows the theory of a percolation system, and the charge transport shows different models. The temperature dependence of the electrical conductivity for the composites shows that both positive (PTC) and negative (NTC) temperature coefficients appear near the melting temperature of matrix. The NTC behaviors within the temperature range below the melting point depend on the MWNTs concentration and the NTC intensity increases with the increasing MWNTs concentration.     

Thermo-physical properties of epoxy nanocomposites reinforced with amino-functionalized multi-walled carbon nanotubes

The modification of multi-walled carbon nanotubes (MWNTs) with amine groups was investigated by FTIR, Raman spectroscopy and XPS after such steps as carboxylation, acylation and amidation. Nanotube-reinforced epoxy polymer composites were prepared by mixing amino-functionalized MWNTs with epoxy resin and curing agent. DSC, TGA, SEM and flexural test were used to investigate the thermal and mechanical properties of the composites. The results showed that amino-functionalized MWNTs could enhance the interfacial adhesion between the nanotubes and the matrix, thus greatly improve the thermal and mechanical properties of the resin epoxy bulk material.     

Effect of multi-wall carbon nanotubes on the mechanical properties of natural rubber

Multi-walled carbon nanotubes (MWNTs) were used to prepare natural rubber (NR) nanocomposites. Our first effort to achieve nanostructures in MWNTs/NR nanocomposites were formed by incorporating carbonnanotubes in a polymer solution and subsequently evaporating the solvent. Using this technique, nanotubess can be dispersed homogeneously in the NR matrix in an attempt to increase the mechanical properties of these nanocomposites. The properties of the nanocomposites such as tensile strength, tensile modulus, tear strength, elongation at break and hardness were studied. Mechanical test results show an increase in the initial modulus for up to 12 times in relation to pure NR. In addition to mechanical testing, the dispersion state of the MWNTs into NR was studied by transmission electron microscopy (TEM) in order to understand the morphology of the resulting system. According to the present study, application of the physical and mechanical properties of carbon nanotubes to NR can result in rubber products which have improved mechanical, physical and chemical properties, compared with existing rubber products reinforced with carbon black or silicone.     

Preparation, morphology and properties of acylchloride-grafted multiwall carbon nanotubes/fluorinated polyimide composites

A fluorinated polyimide (PI) was synthesized by a two-step reaction from 4,4′-(hexafluoroisopropylidene) diphthalic anhydride and 2,2′-bis(trifluoromethyl)-4,4′diaminobiphenyl. A series of PI composites with various mass fractions of multi-walled carbon nanotubes (MWNTs) were prepared by either an in situ polymerization or blending process. To increase the chemical compatibility of carbon nanotubes with the PI matrix, MWNTs were treated with an acid mixture and sulfoxide chloride by turns. Results show that the dispersion of the MWNTs is highly improved in the PI by modification. The modified MWNTs are dispersed homogeneously in the matrix, while the structures of the PI and MWNTs are stable in the preparation process. The thermal stability of the nanocomposites is slightly lower than that of the pure PI. With incorporating MWNTs, the storage modulus and glass transition temperature of the composite films enhanced comparing to that of PI matrix. The dielectric constants of the composites increase sharply, which is favorable to their practical use in anti-static materials and embedded capacitors.     

CNTs/ UHMWPE composites with a two-dimensional conductive network

A low percolation threshold can be achieved for the conductive polymer composites(CPC) materials having a segregated structure in which the conductive particles like carbon black (CB), carbon nanotubes (CNTs), etc. are only located on the interface of the polymer matrix particles instead of being randomly distributed in the whole system. Multiwalled carbon nanotubes (MWNTs) were experienced alcohol-assisted dispersion under ultrasonication and intense mechanical mixing, and only located on the interfaces of the ultrahigh molecular weight polyethylene (UHMWPE) matrix particles to form a segregated structure. The morphological observation and the critical exponent t value obtained from the classical threshold mechanism indicate that the MWNTs/UHMWPE composites form a 2-dimension conductive network, which leads to a very low percolation of 0.072vol%.     

酸处理碳纳米管/PBO复合材料的制备与表征

用原位聚合法成功地制备了碳纳米管/聚对苯撑苯并双口恶唑(PBO)复合材料。用FT-IR、XPS、SEM和AFM对碳纳米管和所制备的复合材料进行了表征,结果表明,碳纳米管的酸处理效果好,表面含有C-O、COOH等极性官能团;复合材料中碳纳米管在聚合物基体中分散均匀,两相界面间存在较强的作用力。     

Effect of dispersion condition of multi-walled carbon nanotube (MWNT) on bonding properties of solderable isotropic conductive adhesives (ICAs)

Carbon nanotubes have been considered as reinforcements in composite materials because of their exceptional mechanical, electrical, and thermal properties. In this paper, the effect of dispersion conditions of multi-walled carbon nanotubes (MWNTs) on bonding properties of solderable isotropic conductive adhesives (ICA) was investigated. Two types of ICAs, untreated pristine MWNT-filled ICAs and acid-treated MWNT (a-MWNT)-filled ICAs were formulated with 1 wt% MWNTs and 83 wt% low-melting-point alloy (LMPA) fillers. X-ray photoelectron spectroscopy analysis was conducted to characterize the surface chemical states of pristine and a-MWNTs and verify the effectiveness of a-MWNTs. The fracture surface of the polymer matrix and solderable ICAs with a-MWNTs showed good dispersion conditions through field-emission scanning electron microscope. After the interconnection process, the a-MWNT-filled solderable ICA showed uniform dispersion of MWNTs in the polymer matrix and formed a stable metallurgical conduction path because of the good rheology-coalescence-wetting behavior of LMPA. Alternatively, pristine MWNT-filled ICA showed poor dispersion and an unstable conduction path formed by aggregated MWNTs.     

Synthesis and characterization of processable multi-walled carbon nanotubes-sulfonated polydiphenylamine graft copolymers

Water soluble and processable nanocomposites composed of multi-walled carbon nanotubes (MWNTs) and poly(diphenylamine sulfonic acid) (PDPASA) are synthesized and characterized. Two types of methodologies are adopted. MWNTs are covalently functionalized with 2,5-diaminobenzene sulfonic acid (DABSA) and further in situ polymerized with diphenylamine-4-sulfonic acid (DPASA). This results in the formation of nanocomposites, MWNT(DABSA)-g-PDPASA, in which PDPASA is presented as the graft chains onto MWNTs. In another approach, DPASA is in situ polymerized in presence of unfunctionalized MWNTs, results in a nanocomposite in which MWNTs are present as entrapped mass in PDPASA matrix. Both nanocomposites are found to be water soluble and can form free standing films. The conductivity of MWNT(DABSA)-g-PDPASA and MWNT/PDPASA is found to be 1.25 mS x cm(-1) and 0.65 mS x cm(-1), respectively, which is higher than that of pristine PDPASA (0.25 x 10(-5) S x cm(-1)). The nanocomposites are characterized for their structure, morphology, optical and thermal properties.     

Effect of pyrene-modified multiwalled carbon nanotubes on the properties of epoxy composites

The block polymer of poly(styrene-b-pyrene) (PS-b-PAH) containing pyrene units was successfully applied on the surface of multiwalled carbon nanotubes (MWNTs) and the properties of nanocomposites were enhanced. The morphology of the modified MWNTs was characterized by transmission electron microscopy (TEM), and the results showed that PS-b-PAH helped effectively the MWNTs to disperse well in epoxy matrices, and these dispersed MWNTs were stabilized by the pyrene modifier. The mechanical properties of the composites, such as impact toughness and flexural strength, and the electrical conductivity of the nanocomposites, are improved significantly after the treatment of the MWNTs using PS-b-PAH. The results show that the mechanical and electrical properties of the modified MWNTs/epoxy composites with PS-b-PAH are obviously superior to those of pristine MWNTs/epoxy composites. The enhanced interfacial interactions lead to good dispersion of MWNTs in epoxy matrices, thus enhancing the mechanical and electrical properties of the nanocomposites.