Coagulation method for preparing single-walled carbon nanotube/poly(methyl methacrylate) composites and their modulus,electrical conductivity,and thermal stability

A coagulation method providing a better dispersion of single-walled carbon nanotubes (SWNTs) in a polymer matrix was used to produce SWNT/poly(methyl methacrylate) (PMMA) composites. Optical microscopy and scanning electron microscopy showed an improved dispersion of SWNTs in the PMMA matrix, a key factor in composite performance. Aligned and unaligned composites were made with purified SWNTs with different SWNT loadings (0.1–7 wt %). Comprehensive testing showed improved elastic modulus, electrical conductivity, and thermal stability with the addition of SWNTs. The electrical conductivity of a 2 wt % SWNT composite decreased significantly (>10⁵) when the SWNTs were aligned, and this result was examined in terms of percolation. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 3333–3338, 2003     

CVD法制备单壁碳纳米管的纯化与表征

针对CVD法合成的单壁碳纳米管的特点提出了较为有效的纯化方法，并对纯化后碳管的存在形式进行了表征.结果表明,CVD法制备的单壁碳纳米管中所含的载体和催化剂绝大部分可以通过盐酸除去.在表面活性剂溶液中超声分散碳纳米管,可以使管与无定形碳及石墨状碎片进行有效的剥离.空气加热氧化法和稀硝酸回流法可有效地去除碳杂质,稀硝酸回流可以在纯化的同时对管的末端及侧壁进行功能化.     

Reversible dispersion of single-walled carbon nanotubes based on a CO2-responsive dispersant

A CO(2)-responsive dispersant, N,N-dimethyl-N'-(pyren-1-ylmethyl) acetimidamidinium (PyAH(+)), which bears both a pyrene moiety and an amidinium cation, has been successfully synthesized. Through strong π-π interaction between the pyrene moiety and single-walled carbon nanotubes (SWNTs), we have demonstrated that PyAH(+) can be modified onto SWNT surfaces to promote the dispersion of SWNTs in water. Furthermore, taking advantage of gas triggered interconversions between the amidinium cation and amidine, reversible control on the solubility of SWNTs has been achieved simply through alternated bubbling of CO(2) and Ar. This work has demonstrated a new method for controlled dispersion and aggregation of SWNTs, and it may contribute to the development of gas responsive carbon materials.     

Synergistically Enhanced Dispersion of Native Protein–Carbon Nanotube Conjugates by Fluoroalcohols in Aqueous Solution

Carbon nanotubes (CNTs) are anticipated as an important new material for use in nanotechnology applications because of their excellent mechanical and electrical properties. For their development, a highly stable dispersion of debundled CNTs is indispensable. Herein we present a new method to enhance dispersibility of single‐walled carbon nanotubes (SWNTs) with proteins using alcohols as co‐solvents. Addition of fluoroalcohols in solution increased the SWNT dispersion by more than one order of magnitude without protein denaturation. Enhancement of SWNT dispersion through addition of alcohols was attributed to the decreased hydrophobic interaction among SWNTs. This novel approach enables us to produce biofunctional CNTs such as one‐dimensional nanobiosensors and drug carriers that can penetrate cells.     

Synthesis of block polyethers with various structures and their application in dispersing single-walled carbon nanotubes

The block polyethers with different structure and composition were synthesized by anionic polymerization and used to disperse single-walled carbon nanotubes (SWNTs). The block polyethers with the structure of branch or benzene ring had better dispersion ability than the commercial Pluronic block polyethers (L64 and F127). In order to compare the parameters, dispersion limit and efficiency of polyethers for SWNTs were defined. UV?Cvis?Cnear infrared absorbance spectra showed that eight-branch polyether AE82 had much larger dispersion limit and efficiency than five-branch AE52. BPE containing benzene rings in the molecule had a slightly lower dispersion limit but larger dispersion efficiency than AE82. The defect density of SWNTs dispersed in polyether aqueous solutions was investigated by Raman spectroscopy. The polyethers AE83 and BEP with the structure of poly(ethylene oxide)?Cpoly(propylene oxide) dispersed less defective SWNTs than AE82 and BPE, indicating that the variation of polyether structure and composition could influence the defect density of SWNTs besides dispersion limit and efficiency.     

PET-SWNT nanocomposites through ultrasound assisted dissolution-evaporation

Poly(ethylene terephthalate) (PET) based nanocomposites have been prepared with single walled carbon nanotubes (SWNTs) through an ultrasound assisted dissolution-evaporation method. Differential scanning calorimetry studies showed that SWNTs nucleate crystallization in PET at weight fractions as low as 0.3%, as the nanocomposite melt crystallized during cooling at temperature 24 °C higher than neat PET of identical molecular weight. Isothermal crystallization studies also revealed that SWNTs significantly accelerate the crystallization process. Mechanical properties of the PET-SWNT nanocomposites improved as compared to neat PET indicating the effective reinforcement provided by nanotubes in the polymer matrix. Electrical conductivity measurements on the nanocomposite films showed that SWNTs at concentrations exceeding 1 wt% in the PET matrix result in electrical percolation. Comparison of crystallization, conductivity and transmission electron microscopy studies revealed that ultrasound assisted dissolution-evaporation method enables more effective dispersion of SWNTs in the PET matrix as compared to the melt compounding method.     

Improving the effectiveness of interfacial trapping in removing single-walled carbon nanotube bundles

Single-walled carbon nanotube (SWNT) bundles are selectively removed from an aqueous dispersion containing individually suspended carbon nanotubes coated with gum Arabic via interfacial trapping. The suspensions are characterized with absorbance, fluorescence, and Raman spectroscopy as well as atomic force microscopy (AFM) and rheology. The resulting aqueous suspensions have better dispersion quality after interfacial trapping and can be further improved by altering the processing conditions. A two-step extraction process offers a simple and fast approach to preparing high-quality dispersions of individual SWNTs comparable to ultracentrifugation. Partitioning of SWNTs to the liquid-liquid interface is described by free energy changes. SWNT bundles prefer to reside at the interface over individually suspended SWNTs because of greater free energy changes.     

Dispersing carbon nanotubes using surfactants

We review the recent advances in dispersing single-wall carbon nanotubes (SWNTs) using amphiphilic surfactants in aqueous solutions. Three aspects are discussed. (1) On the organization of surfactant molecules with SWNTs, new insights at the microscopic level arise from electron microscopy and detailed computer simulation studies. (2) Quantitative measurements, such as molecular interactions between functional groups and SWNTs, the coverage of surfactant on SWNTs in solution, the charge state of the SWNT/surfactant complex, and the degree of dispersion are critical for better understanding dispersion mechanisms and for the further development of dispersion strategies. (3) The thermodynamic driving forces and the role of metastability in the structure of surfactant dispersed SWNT suspensions are analyzed. An outlook on practical and fundamental issues is also presented.     

Evaluation of the addition of various surfactant-suspended carbon nanotubes in MEEKC with an in situ-synthesized surfactant system

Dispersions of single-walled carbon nanotubes (SWNTs) in various surfactant solutions have been systematically evaluated as additives in MEEKC. The compounds examined were catechins, phenolic acids, and flavonoids. Compared with zwitterionic and neutral surfactants, the addition of anionic dispersion seemed to be better at separating the three types of analytes in microemulsion system. In order to achieve low operating currents, an in situ-synthesized surfactant system based on the combination of a long-chain alkyl acid with an organic base was used in MEEKC. The optimized buffer contained 0.5% (57?mM) ethyl acetate, 0.6% (30?mM) lauric acid, 4.0% (666?mM) propanol, 50?mM Tris solution, and 4.5?mg/L the dispersion of SWNTs. Under optimized conditions, the established method was applicable to quantify complex compounds in tea samples.     

A biomimetic "polysoap" for single-walled carbon nanotube dispersion

As-synthesized single-walled carbon nanotubes (SWNTs) are bundled mixtures of different species. The current challenge in the field of carbon nanotube research lies in the processing and separation of SWNTs, which first require efficient dispersion of individual SWNTs in solvents. We report DNA-mimicking polysoap surfactants that disperse SWNTs in aqueous solutions more effectively than DNA. The polysoaps are synthesized by functionalizing the side chain of poly(styrene-alt-maleic acid) with aminopyrene. The synthetic nature of the polysoap opens a new approach to further optimization of not only SWNT dispersion efficiency but also multi-functional SWNT dispersing surfactant.     

Importance of aromatic content for peptide/single-walled carbon nanotube interactions

We have previously demonstrated that a designed amphiphilic peptide helix, denoted nano-1, coats and debundles single-walled carbon nanotubes (SWNTs) and promotes the assembly of these coated SWNTs into novel hierarchical structures via peptide-peptide interactions. The purpose of this study is to better understand how aromatic content impacts interactions between peptides and SWNTs. We have designed a series of peptides, based on the nano-1 sequence, in which the aromatic content is systematically varied. Atomic force microscopy measurements and optical absorption spectroscopy reveal that the ability to disperse individual SWNTs increases with increasing aromatic residues in the peptide. Altogether, the results indicate that pi-stacking interactions play an important role in peptide dispersion of SWNTs.     

Preparation and characterization of a carbon nanotube-lyotropic liquid crystal composite

We present a detailed study on the integration of individual single-walled carbon nanotubes (SWNTs) within a lyotropic hexagonal liquid crystal (LC) for the first time. Two systems are studied in this work; in the first, the same surfactant is used for both the dispersion of the SWNTs and the formation of the LC. In the second system, we use different surfactants for the dispersion of SWNTs and LC formation. Light microscopy imaging combined with small-angle X-ray scattering (SAXS) indicates that the nanotubes (NTs) are well dispersed and aligned along the LC director. The macroscopic property, namely, the viscosity, is strongly enhanced by the presence of the NTs.     

Influence of Polymer Electronics on Selective Dispersion of Single‐Walled Carbon Nanotubes

The separation and isolation of semiconducting and metallic single‐walled carbon nanotubes (SWNTs) on a large scale remains a barrier to many commercial applications. Selective extraction of semiconducting SWNTs by wrapping and dispersion with conjugated polymers has been demonstrated to be effective, but the structural parameters of conjugated polymers that dictate selectivity are poorly understood. Here, we report nanotube dispersions with a poly(fluorene‐co‐pyridine) copolymer and its cationic methylated derivative, and show that electron‐deficient conjugated π‐systems bias the dispersion selectivity toward metallic SWNTs. Differentiation of semiconducting and metallic SWNT populations was carried out by a combination of UV/Vis‐NIR absorption spectroscopy, Raman spectroscopy, fluorescence spectroscopy, and electrical conductivity measurements. These results provide new insight into the rational design of conjugated polymers for the selective dispersion of metallic SWNTs.     

单壁碳纳米管与卤代烷的亲电加成反应

主要考察了以路易斯酸为催化剂,几种卤代烷烃为反应试剂的单壁碳纳米管侧壁的亲电加成反应,并通过傅立叶红外光谱、热失重分析和拉曼光谱验证了实验所得产物。此反应的目的是在单壁碳纳米管的侧壁连上烷基基团以提高其溶解性和分散性,并可使其更好地与聚烯烃相结合从而提高复合材料的性能,因而具有较高的研究和应用价值。     

Cellulose Nanocrystal-Assisted Dispersion of Luminescent Single-Walled Carbon Nanotubes for Layer-by-Layer Assembled Hybrid Thin Films

Highly stable single-walled carbon nanotube (SWNT) dispersions are obtained after ultrasonication in cellulose nanocrystal (CN) aqueous colloidal suspensions. Mild dispersion conditions were applied to preserve the SWNT length in order to facilitate the identification of hybrid objects. This led to a moderate dispersion of 24% of the SWNTs. Under these conditions, atomic force microscopy (AFM) and transmission electron microscopy (TEM) experiments succeeded in demonstrating the formation of hybrid particles in which CNs are aligned along the nanotube axis by a self-assembly process. These SWNT/CN dispersions are used to create multilayered thin films with the layer-by-layer method using polyallylamine hydrochloride as a polyelectrolyte. Homogeneous films from one to eight bilayers are obtained with an average bilayer thickness of 17 nm. The presence of SWNTs in each bilayer is attested to by characteristic Raman signals. It should be noted that these films exhibit a near-infrared luminescence signal due to isolated and well-separated nanotubes. Furthermore, scanning electron microscopy (SEM) suggests that the SWNT network is percolating through the film.     

Light-controlled single-walled carbon nanotube dispersions in aqueous solution

We have succeeded in dispersing single-walled carbon nanotubes (SWNTs) into an aqueous solution of poly(ethylene glycol)-terminated malachite green derivative (PEG-MG) through simple sonication. It was found that UV exposure caused reaggregation of these predispersed SWNTs in the same aqueous medium, as adsorbed PEG-MG photochromic chains could be effectively photocleavaged from the nanotube surface. The observed light-controlled dispersion and reaggragation of SWNTs in the aqueous solution should facilitate the development of SWNT dispersions with a controllable dispersity for potential applications.     

RBM band shift-evidenced dispersion mechanism of single-wall carbon nanotube bundles with NaDDBS

The dispersion process of single-wall carbon nanotube (SWNT) by using sodium dodecylbenzene sulfonate (NaDDBS) was studied by means of surface tension measurements, ultraviolet-visible (UV-Vis) spectroscopy, scanning electron microscopy (SEM), and transmission electron spectroscopy (TEM). The critical micelle concentration (CMC) and the concentration where the surface tension begins to drop increase by the presence of SWNT. The isotherm of NaDDBS amount adsorbed on SWNT shows the plateau region at 0.2-6 mM and the saturated region above 40 mM. The external surface of SWNT bundle is fully covered with adsorbed NaDDBS at the plateau region, showing that SWNTs can be dispersed with the bundle form. On the other hand, SWNTs are dispersed in individual tubes at the saturated region, where the adsorption amount corresponds to coating of individual tube surfaces with NaDDBS. This dispersion state was confirmed by SEM and TEM observations. The effect of the dispersion state of SWNTs on radial breathing mode in Raman spectrum gave inherent peak shifts, being the in situ evidences on the step-wise dispersion mechanism of the SWNT bundle to the individual tubes.     

Continuous spinning of a single-walled carbon nanotube-nylon composite fiber

We report a chemical processing technology that allows the continuous spinning of single-walled carbon nanotubes (SWNTs)-nylon 6 (PA6) fibers by the in-situ polymerization of caprolactam in the presence of SWNTs, which simultaneously optimizes the morphology of the composite. We show that caprolactam is an excellent solvent for carboxylic-acid-functionalized SWNTs (SWNT-COOH) and that this allows the efficient dispersal of the SWNTs and subsequent grafting of PA6 chains to the SWNTs through condensation reactions between the carboxylic-acid group on SWNT-COOH and the terminal amine group of PA6. The existence of a graft copolymer between the PA6 chains and the SWNTs is demonstrated by IR, TGA, and AFM studies, and we show that the solubility of the polymerized material in formic acid is controlled by the degree of graft copolymerization. The amount of grafted PA6 chains that are attached to the SWNTs can be adjusted by controlling the concentration of the initiator (6-aminocaproic acid). The process leads to a uniform dispersion of the SWNTs, and the presence of the graft copolymer increases the polymer/SWNT compatibility while strengthening the interfacial interaction between the nanotube and matrix. The Young's modulus, tensile strength, and thermal stability of the SWNT-reinforced composite fibers produced by this process are significantly improved.     

A triptycene-based approach to solubilising carbon nanotubes and C60

We describe herein the synthesis of a triptycene-based surfactant designed with the ability to solubilise single-walled carbon nanotubes (SWNTs) and C(60) in water through non-covalent interactions. Furthermore, an amphiphilic naphthalene-based surfactant with the same ability to solubilise SWNTs and C(60) has also been prepared. The compounds synthesised were designed with either two ionic or non-ionic tails to ensure a large number of supramolecular interactions with the solvent, thereby promoting strong solubilisation. The surfactants produced stable suspensions in which the SWNTs are dispersed and the surfactant/SWNT complexes formed are stable for more than one year. UV/Vis/NIR absorption spectroscopy, TEM and AFM were employed to probe the solubilisation properties of the dispersion of surfactants and SWNTs in water.     

Phonon vibrational frequencies of all single-wall carbon nanotubes at the lambda point: reduced matrix calculations

With a simple method-the reduced matrix method, we simplified the calculation of the phonon vibrational frequencies according to SWNTs structure and their phonon symmetric property and got the dispersion properties of all SWNTs at Gamma point in Brillouin zone, whose diameters lie between 0.6 and 2.5 nm. The calculating time is shrunk about 2-4 orders. A series of the dependent relationships between the diameters of SWNTs and the frequencies of Raman and IR active modes are given. Several fine structures including "glazed tile" structures in omega approximately d figures are found, which might predict a certain macro-quantum phenomenon of the phonons in SWNTs.