Carbon microfibers sheathed with aligned carbon nanotubes: towards multidimensional, multicomponent, and multifunctional nanomaterials

Multicomponent and multifunctional hybrid structures based on microsized carbon fibers sheathed with aligned carbon nanotubes and their derivatives have been successfully prepared, and have been demonstrated to be an effective means for connecting nanoscale entities to the outside world and to possess interesting electrochemical properties attractive for a wide range of potential applications, including in methanol direct fuel cells and highly sensitive biological and chemical sensors. Judicious modification of the carbon-fiber-supported aligned carbon nanotubes with various functional moieties could lead to a class of novel multidimensional, multicomponent, and multifunctional materials of practical significance.     

Spectroscopic evidence and molecular simulation investigation of the pi-pi interaction between pyrene molecules and carbon nanotubes

The pi-pi interaction between pyrene molecules and single-walled carbon nanotubes (SWNTs) or multi-walled carbon nanotubes (MWNTs) was studied by fluorescence, FTIR, Raman spectroscopy and molecular simulation. The carbon nanotubes were incubated in pyrene solution and dried for characterization. A broadband fluorescence emission at 463 nm of the incubated samples was observed, which is similar to that of pyrene excimers but shifts to shorter wavelength. The typical FTIR bands of pyrene shift to lower wavenumbers in the incubated samples. D- and G-bands in Raman spectra of SWNTs also shift to low frequencies. All these spectroscopic evidences reveal the stronger pi-pi stacking interaction between the nanotubes and pyrene molecules over the pyrene dimers, which leads to the formation of pyrene-carbon nanotube complexes. The systems of SWNTs and pyrene molecules were also studied with molecular simulation. It was found from the binding energy calculation that a stronger interaction presents between the pyrene molecule and the nanotube. In addition, the simulation gives some structural information about the pyrene-nanotube complex, such as the staggered conformation of pyrene on nanotube. The effect of defects in carbon nanotube sidewall was also discussed.     

嵌段共聚物修饰多壁碳纳米管

为了改善多壁碳纳米管的分散性,通过丙烯酸和羟基化多壁碳纳米管的酯化反应将双键引入到碳纳米管的表面,同时利用原子转移自由基聚合合成端基为卤素的苯乙烯-b-甲基丙烯酸羟乙酯嵌段共聚物,并通过对双键的加成反应,将嵌段共聚物引入到多壁碳纳米管的表面,实现了碳纳米管的化学修饰。通过FTIR、TGA和TEM技术对产物进行了表征,结果表明:嵌段共聚物通过共价键接枝到碳纳米管表面,其含量为42.9%,平均约277个碳原子接枝一条聚合物链;修饰后的MW CNTs在乙醇中分散良好。     

RAFT聚合方法在碳纳米管表面接枝嵌段共聚物

首先在碳纳米管表面接上可用做RAFT聚合的链转移剂——二硫代碳酸酯,然后用这些管壁接有二硫代碳酸酯的碳纳米管作为链转移剂引发甲基丙烯酸甲酯和苯乙烯单体进行可控的嵌段聚合反应,首次报道了采用二步加料方式在碳纳米管的管壁上接枝上嵌段共聚物链。对嵌段共聚物的结构进行了红外光谱(FT-IR)、热重分析(TGA)、透射电镜(TEM)表征。     

Functionalization of multi-walled carbon nanotubes with bis(2,2':6',2"-terpyridine) ruthenium(II)-connected diblock polymer

Multi-walled carbon nanotubes (MWCNTs) were functionalized with a bis(2,2':6',2"-terpyridine) ruthenium(ll)-connected diblock poly(N-isopropyacryamide) (RuTpyPNIPAM) by a simple methodology of covalent amidation. The composition and structure of the functionalized ruthenium multi-walled carbon nanotubes (RuMWCNTs) were characterized by thermogravimetric analysis, Fourier transform infrared spectroscopy (FTIR), Raman spectroscopy and scanning electron microscopy (SEM). These characterization methods confirm that after functionalization, ruthenium metallopolymer are interconnected or attached as aggregated structures on the surface of the carbon nanotubes.     

Spectroscopic probing of organic molecules encapsulated in functionalized carbon nanotubes in solution

Pyrene was introduced into cavities in functionalized single-walled and multiple-walled carbon nanotubes to be used as a molecular probe in the study of encapsulation. The solubility of these materials in common organic solvents allowed solution-phase absorption and emission spectroscopic measurements. The results, which are consistent with the formation of pyrene excimer, are explained in terms of high local pyrene concentrations and perhaps pyrene microcrystals inside the carbon nanotube cavities. The fluorescence decay results show that there is significant quenching of pyrene excited states by the hosting carbon nanotubes.     

Dispersion of single-walled carbon nanotubes in water by the use of novel fluorinated dendrimer-type copolymers

New fluorinated dendrimer-type block copolymers were applied to the dispersion of single-walled carbon nanotubes (SW-CNTs) and single-walled carbon nanotubes containing carboxy groups [(SW-CNT)-COOH] in water. Fluorinated block copolymer could disperse SW-CNTs more effectively in water, compared to that of the corresponding ABA triblock-type fluoroalkyl end-capped dimethylacrylamide oligomer [R_F-(DMAA)_n-R_F]. Dynamic light-scattering (DLS) measurements and transmission electron microscopy (TEM) images show that SW-CNTs could be smoothly encapsulated into fluorinated copolymeric aggregates cores. Interestingly, it was demonstrated that SW-CNTs could be in part released from the fluorinated copolymeric aggregates/SW-CNTs composites or encapsulated into these composites with increasing the dispersion times. On the other hand, fluorinated block copolymer and R_F-(DMAA)_n-R_F oligomer were not able to disperse well (SW-CNT)-COOH in water; however, ABA triblock-type fluoroalkyl end-capped acrylic acid oligomer was able to disperse quite effectively (SW-CNT)-COOH in water.     

Noncovalent functionalization of multi-walled carbon nanotubes with amphiphilic polymers containing pyrene pendants

A novel noncovalent approach was developed for the functionalization of multiwalled carbon nanotubes (MWNTs) using an amphiphilic copolymer of PVP-co-PAH containing pyrene pendants. A homogeneous polymer layer was formed on the surface of MWNTs, and the wrapped copolymer layer with a thickness of about 17.7 nm was found. The noncovalent modified MWNTs were dispersed very well in solvent of dimethylformamide (DMF), water and chloroform (CHCl₃), and the high stability of dispersed suspensions could be maintained for more than 2 months without observed MWNT precipitation. In addition, the dispersing behavior of the noncovalent functionalized MWNTs by PVP-co-PAH in a solvent mixture of water/CHCl₃ was also investigated, and it was found that a carbon nanotube layer was formed at the water/CHCl₃ interface.     

新型Ru(Ⅱ)配合物的合成及其自组装膜的光电性能

合成了含芘基的新型钌(Ⅱ)配合物Ru-1,用1H-NMR和MS表征了这种配合物的分子结构。TG-DSC测试结果表明,Ru-1在一个较宽的温度范围内具有良好的热稳定性。在HOPG、石墨烯基电极表面组装了钌配合物分子膜,并对其进行了AFM、电化学及紫外可见吸收光谱等光电化学分析。结果表明,自组装膜的生长是均匀的,膜材料具有可逆的氧化还原过程,在0.47 V出现可逆的氧化还原峰。紫外可见吸收光谱表明,这种膜材料在较宽的紫外可见区表现出强且宽的吸收峰。钌配合物对石墨烯、HOPG炭素电极的修饰,使这类炭素电极具有良好的光电性能和稳定性。     

嵌段共聚物及其在有序介孔材料制备中的研究进展

介绍了近年来嵌段共聚物及其在制备有序孔材料中的应用与发展。综述了嵌段共聚物的结构特点、制备方法、自组装机理及利用嵌段共聚物自组装和利用嵌段共聚物作为模板剂制备有序介孔材料,指出了嵌段共聚物在制备有序介孔材料应用中的优点、社会价值和需要解决的问题。     

Templated growth of carbon nanotubes with controlled diameters using organic-organometallic block copolymers with tailored block lengths

Block copolymer thin films fabricated from polystyrene-polyferrocenylsilane (PS-b-PFS) block copolymers on silicon substrates were used as precursors of well-ordered, nanosized growth catalysts for carbon nanotubes (CNTs). The size of the catalytic domains was tuned by changing the molecular weight of the block copolymer, enabling control of the diameter of the CNTs grown from these substrates. CNT growth on catalytic substrates with larger organometallic domain sizes, using acetylene as a carbon source, resulted in enhanced amounts of CNT deposition compared to smaller PFS domains, which exhibited low catalytic activity. The inner and outer diameters of the multi-walled CNTs obtained were typically 8 and 16 nm, respectively, and were not influenced by the catalytic domain sizes. Various annealing strategies in inert or in hydrogen atmosphere were investigated. The use acetylene with an additional hydrogen flow as gas feed resulted in a significant increase in deposition on all PS-b-PFS decorated substrates. Under these conditions, the CNT diameters could be controlled by the catalyst domain sizes, resulting in decreasing diameters with decreasing domain sizes. Multiwalled CNTs with inner and outer diameters of 4 and 7 nm, respectively, and a narrow diameter distribution were obtained.     

Chemically Tailored Multifunctional Asymmetric Isoporous Triblock Terpolymer Membranes for Selective Transport

Membrane-based separation of organic molecules with 1–2 nm lateral dimensions is a demanding but rather underdeveloped technology. The major challenge is to fabricate membranes having distinct nanochannels with desired functionality. Here, a bottom-up strategy to produce such a membrane using a tailor-made triblock terpolymer featuring miscible end blocks with two different functional groups is demonstrated. A scalable multifunctional integral asymmetric isoporous membrane is fabricated by the solvent evaporation-induced self-assembly of the block copolymer combined with nonsolvent-induced phase separation. The membrane nanopores are readily functionalized using positively and negatively charged moieties by two straightforward gas–solid reactions. The pores of the post-functionalized membranes act as target-specific functional soft nanochannels due to swelling of the polyelectrolyte blocks in a hydrated state. The membranes show unprecedented separation selectivity of small molecules based on size and/or charge which demonstrates the potential of the proposed strategy to prepare next-generation nanofiltration membranes.     

Compressive properties of nanoparticle modified epoxy resin at different strain rates

Epoxy resins often exhibit high strength yet are often brittle, especially at high strain rates. Block copolymer modified epoxy resins have generated significant interest since it was demonstrated that the combination could lead to nanostructured thermosets through the self-assembly of the block copolymer. Such nanostructured epoxies exhibit increased ductility without the significant loss in yield strength exhibited by traditional rubber-modified epoxies. In this study, the effect of different nanoscale additives on the compressive yield strength of a model epoxy resin has been studied. In the first case, a block copolymer styrene-b-butadiene-b-polymethylmethacrylate (SBM) was added to the model epoxy resin. In the second case, carbon nanotubes (CNTs) were added. In the final case, both additives were mixed simultaneously with the epoxy resin. The compressive mechanical behavior of these materials has been investigated over a wide range of strain rates (0.001–3500 s⁻¹). The yield behavior was found to fit the cooperative yield model proposed by Fotheringham and Cherry.     

Electronic properties of ruthenium sulfide–carbon cluster composite material obtained by calcination of an alternating ruthenium–S–phenylene hybrid copolymer

Calcination of an alternating ruthenium–S–phenylene hybrid copolymer under an argon atmosphere was found to give nano-sized ruthenium sulfide/carbon cluster composite material. ESR spectral examinations of the material revealed that an electron transfer from ruthenium sulfide particles to carbon clusters took place to raise a visible-light responsive oxidation–reduction function with an oxidation site at ruthenium sulfide particles and a reduction site at carbon clusters. The surface of the calcined material was modified with Pt particles, and the reduction ability of the resulting modified material was examined.     

含多芳香环嵌段聚合物PS-b-PAH对碳纳米管的修饰

以芘丁酸为原料通过酯化反应制备了含芘丁单元的苯乙烯基单体,再利用原子转移自由基聚合法（ATRP）合成了分子量可控的嵌段聚合物PS-b-PAH,采用凝胶渗透色谱（GPC）、核磁共振（1H-NMR）等测试手段对产物进行了表征。采用聚合物对碳纳米管表面修饰,比较了聚苯乙烯PS和嵌段聚合物PS-b-PAH修饰碳纳米管后在THF...     

Selection of carbon nanotubes with specific chiralities using helical assemblies of flavin mononucleotide

The chirality of single-walled carbon nanotubes affects many of their physical and electronic properties. Current production methods result in nanotubes of mixed chiralities, so facile extraction of specific chiralities of single-walled carbon nanotubes is an important step in their effective utilization. Here we show that the flavin mononucleotide, a common redox cofactor, wraps around single-walled carbon nanotubes in a helical pattern that imparts efficient individualization and chirality selection. The cooperative hydrogen bonding between adjacent flavin moieties results in the formation of a helical ribbon, which organizes around single-walled carbon nanotubes through concentric pi-pi interactions between the flavin mononucleotide and the underlying graphene wall. The strength of the helical flavin mononucleotide assembly is strongly dependent on nanotube chirality. In the presence of a surfactant, the flavin mononucleotide assembly is disrupted and replaced without precipitation by a surfactant micelle. The significantly higher affinity of the flavin mononucleotide assembly for (8,6)-single-walled carbon nanotubes results in an 85% chirality enrichment from a nanotube sample with broad diameter distribution.     

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.     

pH effects on BSA-dispersed carbon nanotubes studied by spectroscopy-enhanced composition evaluation techniques

Dispersion and exfoliation of carbon nanotubes (CNT) by water soluble dispersants such as surfactant, polymer or protein is a key step toward the application of carbon nanotubes in composite materials, biochemical and biomedical applications. Upon dispersion, the solution phase separates into dispersed nanotubes in the supernatant and a precipitate phase including carbonaceous impurities but also nanotubes and dispersants. Yet, simple but accurate tools for measuring the concentrations of the constituents are not available. In most studies a comparison between CNT suspensions is based on ocular observation or on UV-visible measurement of a featureless spectrum at single wavelength. Such measurements are complex since both nanotubes and most dispersants absorb along the whole UV-visible spectrum and an overlap of their signals occurs. In this paper we employ chemometric techniques to evaluate the pH effect on the concentration of both dispersant (protein-bovine serum albumin, BSA) and single-wall nanotube (SWNT) from a full UV-visible spectrum of aqueous solutions. We find strong correlation between the conformation of the protein and its dispersion efficiency.     

碳纳米管／聚氨酯纳米复合材料的制备及性能

采用可逆加成-断裂链转移(RAFT)聚合方法在碳纳米管表面接枝聚甲基丙烯酸甲酯和聚苯乙烯嵌段共聚物MWNT-P(MMA-b-St),对碳纳米管进行改性。采用直接共混法制备碳纳米管/水性聚氨酯纳米复合材料。通过红外光谱(FT-IR)和透射电镜(TEM)对嵌段共聚物的结构进行了表征。碳纳米管加入对乳液成膜性影响不大。热失重分析(TGA)和力学性能测试结果表明,当改性后的碳纳米管含量为聚氨酯固体份的0.75%时,复合材料的热稳定性、拉伸强度和断裂伸长率均较聚氨酯有所提高。     

Mechanical, electrical and electro-mechanical properties of thermoplastic elastomer styrene–butadiene–styrene/multiwall carbon nanotubes composites

Composites of styrene–butadiene–styrene (SBS) block copolymer with multiwall carbon nanotubes were processed by solution casting to investigate the influence of filler content, the different ratios of styrene/butadiene in the copolymer and the architecture of the SBS matrix on the electrical, mechanical and electro-mechanical properties of the composites. It was found that filler content and elastomer matrix architecture influence the percolation threshold and consequently the overall composite electrical conductivity. The mechanical properties are mainly affected by the styrene and filler content. Hopping between nearest fillers is proposed as the main mechanism for the composite conduction. The variation of the electrical resistivity is linear with the deformation. This fact, together with the gauge factor values in the range of 2–18, results in appropriate composites to be used as (large) deformation sensors.