Influence of the functionalization of carbon nanotubes on calendering dispersion effectiveness in a low viscosity resin for VARIM processes

The use of a three roll machine to disperse nanoreinforcements in polymer matrix has been proved as an alternative to chemical routes of dispersion. Nevertheless, the degree of dispersion achieved depends on the nanoreinforcement type and the sequences used in the calendering process. This research work focuses in the evaluation of the differences in the dispersion effectiveness of functionalized and non-functionalized carbon nanotubes (CNTs) in an epoxy resin. This aspect has influence not only on the final properties of the nanocomposites but also on the infiltration process due to changes in the rheological behavior and possible filtering of bigger aggregates. Samples of both types of nanoreinforcements up to percentages of 0.5% in weight were characterized using several techniques before and after the curing stage to evaluate variations in the dispersion of the nanoreinforcement and in the final properties of the two types of nanocomposites. The possibility of using CNT/epoxy mixtures as matrix of multiscale composites has been also evaluated fabricating panels by vacuum assisted resin infusion molding (VARIM).     

Dispersion of carbon nanofibres in a low viscosity resin by calendering process to manufacture multiscale composites by VARIM

The use of mechanical processes, such as calendering, is an interesting method to disperse carbon nanofibres because this technique avoids the use of organic solvents needed in chemical methods. Variations of the process are used by researchers, and further study of the effect of the calendering parameters is still needed. For this reason, the effectiveness of the dispersion of several percentages of carbon nanofibres (0.5–3 wt.%) in epoxy resin using different parameters of the calendering process has been studied in this work. Carbon nanofibres/epoxy nanocomposites and non-cured nanoreinforced mixtures have been characterised. This study showed that the dispersion was enhanced with a Sequential method. Density and thermomechanical properties of nanocomposites manufactured by the selected calendering method were evaluated. The viscosity of the CNF/epoxy mixtures at different percentages of nanoreinforcement was adequate to use them as a matrix in multiscale reinforced composites.     

Dispersion of carbon nanofibres in a low viscosity resin by calendering process to manufacture multiscale composites by VARIM

The use of mechanical processes, such as calendering, is an interesting method to disperse carbon nanofibres because this technique avoids the use of organic solvents needed in chemical methods. Variations of the process are used by researchers, and further study of the effect of the calendering parameters is still needed. For this reason, the effectiveness of the dispersion of several percentages of carbon nanofibres (0.5–3 wt.%) in epoxy resin using different parameters of the calendering process has been studied in this work. Carbon nanofibres/epoxy nanocomposites and non-cured nanoreinforced mixtures have been characterised. This study showed that the dispersion was enhanced with a Sequential method. Density and thermomechanical properties of nanocomposites manufactured by the selected calendering method were evaluated. The viscosity of the CNF/epoxy mixtures at different percentages of nanoreinforcement was adequate to use them as a matrix in multiscale reinforced composites.     

多壁碳纳米管的表面功能化及分散性研究

多壁碳纳米管(MWCNTs)分别经混合、强酸氧化浸泡和酰氯化处理后,再与9,10-二氢-9-氧杂-10-磷杂菲-10-氧化物(DOPO)的衍生物(DHDOPO)进行接枝反应得到表面功能化的MWCNTs。利用傅里叶变换红外光谱仪(FT-IR)、透射电子显微镜(TEM)、扫描电子显微镜(SEM)、热重分析仪(TGA)、紫外-可见分光光度仪(UV-Vis)和沉降实验等分别表征改性前后MWCNTs的结构和表面形态,估算DHDOPO在MWCNTs表面的相对接枝率,研究改性前后MWCNTs在乙醇中的分散性。结果表明,MWCNTs经混合强酸氧化后表面出现羧基;DHDOPO在MWCNTs上的相对接枝率为51%;混合强酸氧化和表面接枝DHDOPO的MWCNTs在无水乙醇中具有良好的分散性。     

Monitoring dispersion of carbon nanotubes in a thermosetting polyester resin

The paper concerns the initial steps in the preparation of carbon nanotube containing nanocomposites of an isophthalic unsaturated polyester resin, prior to cure. Developments in the nature of the rheology of the liquid samples were monitored as a function of the level of energy introduced via ultrasonic horn mixing and related to microscopic observations. On-line sampling, coupled with off-line viscosity measurements, is compared with on-line measurements of electrical resistivity of the mixture, in terms of the relative suitability of these techniques for real-time monitoring of nanofiller dispersion in the liquid mixtures. The shear thinning parameter, N, derived from fitting Carreau model to the shear viscosity data, appears to provide a good qualitative indicator of the state of nanotube dispersion in the sample.     

Effect of cutting and functionalization of single-walled carbon nanotubes on their dispersion behaviors

Cutting of single-walled carbon nanotubes (SWCNTs) and their modification with poly (ethylene glycol) and polystyrene were successfully performed through a treatment of the SWCNTs with piranha solutions and monoamine terminated polymers. The shortening and functionalization of SWCNTs were confirmed through size exclusion chromatography and Raman spectroscopy observations. The shortened SWCNTs exhibited more aggregated morphology than as-prepared SWCNTs in scanning electron microscope and atomic force microscope observations. Cutting and functionalization of SWCNTs with different polymer chains effectively tailored their dispersion behaviors in solvents. Polystyrene composite films exhibited improved transparency employing shortened SWCNTs, suggesting that the size of SWCNTs are critical factors in controlling the transparency of polymer composite films.     

单壁碳纳米管的光解法功能化及其对分散性能的影响(英文)

将单壁碳纳米管分散到溶有光引发剂2-羟基-2-甲基-1-苯基-1-丙醇的四氢呋喃溶液中,在紫外光辐照下,光引发剂裂解生成2-羟基异丙基自由基。通过自由基的偶合反应,2-羟基异丙基自由基偶合到碳纳米管表面。用UV-Vis光谱、FTIR、拉曼光谱、TGA-MS及HRTEM等表征方法,证实在单壁碳纳米管表面引入了羟基。UV-Vis光谱上范霍夫吸收峰的消失表明碳纳米管表面被功能化。羟基化的SWCNTs样品在FTIR光谱中出现的3420cm-1(O—H键)、2930和2859cm-1(烷基C—H键)峰进一步证实了碳纳米管的功能化。拉曼光谱显示,随着SWCNTs的功能化,其切向模式吸收带与杂碳原子吸收带的相对比值(IG/ID)下降。TGA-MS的m/z59峰(400℃)揭示了SWCNTs上存在着异丙醇基团。HRTEM和溶解数据表明,光解改性有助于碳纳米管管束间缠结的解开,进而提高了其在有机溶剂中的溶解性,并且在一定程度上保持了碳纳米管的结构。     

Efficient direct water dispersion of multi-walled carbon nanotubes by functionalization with lysine

A small molecule, lysine, has been attached onto the Multi-Walled carbon nanotubes (MWNTs) by producing acyl chloride on the carboxylic groups associated with the nanotubes. Subsequently, highly water-dispersed nanotubes were obtained. Stable concentration as high as 10 mg/ml was obtained in deionized water that was nearly 2 orders of magnitude higher than that obtained from the acidized MWNTs. The functionalized MWNTs can be dispersed in water under a wide range of pH values (5-14) and exhibit pH responsive. Combining the properties of carbon nanotubes and the versatility and biocompatibility of lysine, these lysine functionalized MWNTs could find potential applications in biological applications. And this method could also be used to functionalize other nanomaterials by lysine.     

碳纳米管共价修饰功能化研究进展

综述了近年来国内外碳纳米管共价修饰功能化的研究进展,功能化后的碳纳米管不仅保持了原有的特异性质,而且还表现出修饰基团参加反应的活性,为碳纳米管的分散、组装及表面反应提供可能。     

Influence of functionalization of multi-walled carbon nanotubes on the properties of ethylene vinyl acetate nanocomposites

Commercially available multiwalled carbon nanotubes (MWNT) were chemically modified by amine, acid and silane and their ethylene vinyl acetate (EVA) based nanocomposites were prepared. Unmodified and modified nanotubes were characterized by thermogravimetry, X-ray diffraction, Raman spectroscopy, X-ray photoelectron spectroscopy and transmission electron microscopy. Early degradation of modified nanotubes from the thermogravimetry study proved the presence of functional groups on nanotube surface. Increase in D-band to G-band ratio and a shift in radial breathing mode peaks from the Raman spectra indicated the generation of surface defects due to functionalization and variation in van der Waals force of attraction between nanotube aggregates on modification. The unmodified nanotubes improved the tensile strength by 30% with 4 weight% of filler. Amine modification imparted further increase in strength due to the presence of functional groups on the nanotube surface and the subsequent better dispersion of the nanotubes in the polymer matrix. The silane treatment imparted maximum improvement in various properties of the nanocomposites. The nanotubes provided better thermal degradation stability and also higher thermal conductivity to virgin EVA. The results were well supported by the morphological as well as swelling study of the various samples.     

Nitrogen plasma functionalization of carbon nanotubes for supercapacitor applications

Surface modification of carbon nanotubes with a simple and fast plasma treatment allows for the design of new nanomaterials with enhanced electrochemical properties. Both structural disorder and nitrogen concentration of the nanotubes increase after a nitrogen plasma treatment. The effect of plasma power and nitrogen pressure on the charge storage capability of the nanotubes has been investigated in detail. Depending on the plasma conditions, nitrogen functionalities such as quaternary nitrogen in the basal planes, and pyrrolic groups at the edges are introduced in the nanotubes structure. The potential difference between anodic and cathodic peaks of the Fe³⁺/Fe²⁺ redox couple decreases from 102 mV down to 75.7 mV after the nitrogen plasma treatment, which accounts for an increased reversibility of the electron transfer process between nanotubes and electrolyte. Moreover, the treated nanotubes show a significant increase in their specific capacitance from 22 up to 55 F g^?1 at a scan rate of 10 mV s^?1 in a 0.1 M Na₂SO₄ solution. Pyridinic and pyrrolic functionalities are found to play an important role in enhancing the reversibility and specific capacitance of the obtained electrodes.     

Influence of dispersion of multi-walled carbon nanotubes on the electrochemical performance of PEDOT-PSS films

In this work, multi-walled carbon nanotubes (MWCNTs) were chemically treated using ethylene glycol (EG) to improve their dispersion in poly(3,4-ethylene dioxythiophene)-poly(4-styrenesulfonate) (PEDOT-PSS). The surface resistance, transmittance, and electrochemical properties of the chemically treated MWCNTs (EG-MWCNT)/PEDOT-PSS films prepared by spray-coating were investigated. The effect of polar solvents on the electrochemical properties of the films was also determined. It was found that the EG-MWCNTs, well dispersed in the PEDOT-PSS, formed a conductive network after spray-coating. The surface resistance and transmittance of the films decreased as the number of coatings increased. The surface resistance of the films was further decreased with the addition of polar solvents. In addition, the current density of the EG-MWCNT/PEDOT-PSS was enhanced remarkably by polar solvent doping. It was noted that polar solvents having a high dielectric constant led to stabilization and high dispersity of the negative charged EG-MWCNTs and provided a screening effect between PEDOT and PSS, resulting in an increase of the electric and electrochemical properties.     

Graphene oxides for homogeneous dispersion of carbon nanotubes

Graphene oxides (GOs) in terms of both structure and property are essentially polyelectrolytes in a two-dimensional sheet configuration. As is well-established in the literature, polyelectrolytes are, in general, good dispersion agents for single-walled carbon nanotubes (SWNTs), which are otherwise in bundles because of strong van der Waals interactions. We report here a study in which GOs were used to disperse SWNTs, both as-purified and separated semiconducting SWNTs, for solution-like homogeneous suspensions. As a demonstration for their potentials, the optically transparent dispersions were used in a more accurate determination of the absorptivities for the band-gap transitions in semiconducting SWNTs. Results on exploration of the use of the GO-dispersed SWNTs in the development of unique carbon nanocomposite materials are also presented and discussed.     

Thermoplastic elastomers with multi-walled carbon nanotubes: Influence of dispersion methods on morphology

PBT-block-PTMO thermoplastic elastomers derived from dimethyl terephthalate (DMT), 1,4-butanediol(BD) and poly(tetramethylene glycol) (PTMG) were synthesized in the presence of oxidized multi-walled carbon nanotubes (MWCNTs) by a two-stage process involving transesterification and in situ polycondensation. Two procedures were applied to nanotubes in the polymer matrices were used. In procedure 1, nanotubes were dispersed in DMT + BD before the transesterification, while in procedure 2 nanotubes were dispersed in PTMG after transesterification. The mole ratio of the starting components was selected to produce copolymers with a constant hard to soft segment weight ratio of 45:55. Characterization of the new nanocomposites was performed by transmission electron microscopy (TEM), scanning electron microscopy (SEM), small- and wide-angle X-ray scattering (SAXS/WAXS). A better nanotube dispersion can be achieved when oxidized MWCNTs are added to the DMT + BD monomers before transesterification (procedure 1). Oxidized MWCNTs exhibit strong interfacial adhesion to the polymer matrix for both procedures.     

Chemical functionalization of carbon nanotubes for the mechanical reinforcement of polystyrene composites

An organometallic approach was used to functionalize multiwalled carbon nanotubes with n-butyllithium. This procedure was repeated two more times to achieve a higher degree of multiwalled carbon nanotube functionalization. The functionalized nanotubes have been characterized by Fourier transform infrared and Raman spectroscopy, thermogravimetrical analysis, scanning electron microscopy and sedimentation studies. It was possible to form stable suspensions of the functionalized nanotubes in tetrahydrofuran and they were used to make nanotube polymer composites. The mechanical properties of these new nanotube polymer composites were tested and they were found to show an increase of up to 25% in their Young's moduli and up to 50% in their tensile strength over pure polystyrene.     

Characterization of carbon nanotube 3D-structures infused with low viscosity epoxy resin system

This work presents the use of carbon nanotube (CNT) skeletons and the resin infusion process as a path towards the production of polymer composites with high and well dispersed nanotube content. A general purpose low viscosity epoxy resin was used as matrix in the reported process assessment. Thin CNT papers, called skeletons, were initially produced to obtain CNT networks. The impregnation was made by infiltrating the non-diluted resin through the carbon nanotube structure. The results show the proposed processing approach as one capable of producing well dispersed nanocomposites with high CNT loading (more than 15 wt% CNT by composite weight), which are important for developing high performance structures based on carbon nanotubes with good thermal and electrical conductivity. The absolute mechanical performance was lower than expected, and discussed in light of manufacturing problems detected by microscopy observations under scanning electron microscopy (SEM).     

Effects of covalent functionalization on the biocompatibility characteristics of multi-walled carbon nanotubes

We report the effect of chemical modification of multi-walled carbon nanotubes (MWNTs) on their activation of the human serum complement system, as well as the adsorption of human plasma proteins on MWNTs. Four different types of chemically-modified MWNTs were tested for complement activation via the classical and alternative pathways using haemolytic assays. Human plasma protein binding was also tested using an affinity chromatography technique based on carbon nanotube-Sepharose matrix. Covalent functionalization of MWNTs greatly altered the level of activation of the complement system via the classical pathway. For example, MWNTs functionalised with epsilon-caprolactam or L-alanine showed respectively >90% and >75% reduction in classical pathway activation compared with unmodified MWNTs. These results demonstrate for the first time that these types of chemical modification are able to alter considerably the levels of specific complement proteins bound by pristine MWNTs (used as a control experiment). The reduced levels of complement activation via the classical pathway, that are likely to increase biocompatibility, were directly correlated with the amount of C1q protein bound to chemically modified carbon nanotubes. An inverse correlation was also observed between the amount of complement factor H bound to chemically modified MWNTs and the level of complement consumption via the alternative pathway. Binding of human plasma and serum proteins to pristine and modified MWNTs was highly selective. The chemical modifications studied generally increased nanotube dispersibility in aqueous media, but diminished protein adsorption.     

Brightening of the lowest exciton in carbon nanotubes via chemical functionalization

Using time-dependent density functional theory, we found that chemical functionalization at low concentrations of single-walled carbon nanotubes (SWNTs) locally alters the π-conjugated network of the nanotube surface and leads to a spatial confinement of the electronically excited wave functions. Depending on the adsorbant positions, the chemisorption significantly modifies the optical selection rules. Our modeling suggests that photoluminescent efficiency of semiconducting SWNT materials can be controlled by selective chemical functionalization.     

A novel high yield method for dry functionalization of carbon nanotubes

A novel and high yield (> 80%) dry method to functionalize (dry functionalization) carbon nanotubes (CNTs) using hydrothermal method, is reported here. The hydrothermal solution was prepared with HNO3, H2SO4 and H2O2 (1:3:2 vol. ratios) and reaction was carried out from 120 to 200 degrees C for 24 h. CNTs (multi wall) were kept in a way to avoid the direct contact with the solution. Treatment above 180 degrees C resulted in better functionalization of nanotubes as observed from Fourier transform infrared absorption spectroscopic (FTIR) measurements. Field emission scanning electron microscopic (FESEM) images showed that after functionalization, the nanotubes are seen with open ends, granular surface, twisted and are joined together. These clearly indicate the destruction of the graphite structure on the surface. This indicates that after treatment, CNTs reactivity has increased at the ends as well as at the side walls. X-ray Photoelectron Spectroscopic (XPS) studies show a shift in the C 1s peak position, increase in O 1s peak intensity and appearance of an N 1s peak.