Aligned single‐wall carbon nanotube polymer composites using an electric field

While high shear alignment has been shown to improve the mechanical properties of single‐wall carbon nanotube (SWNT)‐polymer composites, this method does not allow for control over the electrical and dielectric properties of the composite and often results in degradation of these properties. Here, we report a novel method to actively align SWNTs in a polymer matrix, which permits control over the degree of alignment of the SWNTs without the side effects of shear alignment. In this process, SWNTs were aligned via AC field‐induced dipolar interactions among the nanotubes in a liquid matrix followed by immobilization by photopolymerization under continued application of the electric field. Alignment of SWNTs was controlled as a function of magnitude, frequency, and application time of the applied electric field. The degree of SWNT alignment was assessed using optical microscopy and polarized Raman spectroscopy, and the morphology of the aligned nanocomposites was investigated by high‐resolution scanning electron microscopy. The structure of the field induced aligned SWNTs was intrinsically different from that of shear aligned SWNTs. In the present work, SWNTs are not only aligned along the field, but also migrate laterally to form thick, aligned SWNT percolative columns between the electrodes. The actively aligned SWNTs amplify the electrical and dielectric properties of the composite. All of these properties of the aligned nanocomposites exhibited anisotropic characteristics, which were controllable by tuning the applied field parameters. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 1751–1762, 2006     

AC and DC percolative conductivity of single wall carbon nanotube polymer composites

The equations needed to correctly interpret both AC and DC conductivity results of single wall carbon nanotube (SWNT) polymer composites and the scaling of these results onto a single master curve are presented. Brief discussions on the factors that determine the critical volume fraction (?_c) and the percolation exponent (t) are also given. The results for a series of SWNT–polyimide composites are presented and the parameters obtained from fitting these results are discussed. The critical volume fraction for electrical percolation of the present composite was about 0.0005. Results obtained from previous work on SWNT (MWNT)–polymer composites and other percolation systems and the modeling (interpretation) of these results are also discussed and compared. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 3273–3287, 2005     

Piezoresistive characteristics of single wall carbon nanotube/polyimide nanocomposites

A systematic study of the effect of single wall carbon nanotubes (SWCNTs) on the enhanced piezoresistive sensitivity of polyimide nanocomposites from below to above percolation was accomplished. The maximum piezoresistive stress coefficient (Π) of 1.52 × 10^?3 MPa^?1 was noted at just above the percolation threshold concentration (Φ ～ 0.05 wt %) of SWCNT. This coefficient value exceeds those of metallic piezoresistive materials by two orders of magnitude (4.25 × 10^?5 MPa^?1 for aluminum). The high piezoresistive characteristics appear to originate from a change in the intrinsic resistivity of the composite caused by the variation of the tunneling distance between conducting inclusions (SWCNTs) under compression or tension. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 994–1003, 2009     

Dramatic enhancement of carbon nanotube dispersion in polyimide composites by a two‐step amino functionalization approach

Amino modified multiwall carbon nanotubes (MWNTs) are prepared, respectively, by two ways: the conventional one‐step method that directly treats acyl chloride functionalized MWNTs with 4, 4′‐diaminodiphenyl ether (ODA), giving the amino modified MWNT (Di‐MWNT), as well as an improved two‐step method in which acyl chloride functionalized MWNT react with mono‐Boc protected ODA first and then the Boc‐groups are deprotected to provide the amino modified MWNT (NH₂‐MWNT). Anhydride‐terminated polyimide (PI) composite films based on NH₂‐MWNT and Di‐MWNT are fabricated by solution blending and consequent planar casting. The exposed amino groups of NH₂‐MWNT create strong covalent bonds with the anhydride‐terminated polyamide acid in the course of N‐acylation and curing chemical reactions. Solubility examinations of nanotubes and morphologies of the composite films indicate that the dispersion of NH₂‐MWNT is significantly better than Di‐MWNT in PI matrix and NH₂‐MWNT can form connected network throughout the PI matrix which makes the NH₂‐MWNT/PI film presenting superior conductivity. Both morphologies and mechanical properties of the composites show that NH₂‐MWNT has stronger interfacial interaction with the PI matrix. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013 , 51, 3449–3457     

Sulfonated liquid crystalline polyesters as resin matrix for single wall carbon nanotube and nanodiamond composites

The focus of this study is on incorporating pendant sulfonate groups along the backbone of a liquid crystalline polyester (LCPE) with the aim to improve the dispersion of single wall carbon nanotubes (SWNTs) and nanodiamonds (NDs). Two LCPE matrices, one sulfonated (LCPE‐S) and one nonsulfonated reference polymer (LCPE‐R), were successfully synthesized via a melt condensation method using aromatic and aliphatic AB, AA, and BB‐type monomers. Upon the introduction of SWNT and ND particles, the glass transition temperature (T_g) of the sulfonated LCPE increased from 21.5 °C to 41.0 °C and 41.9 °C, for SWNTs and NDs, respectively. When sulfonate groups were absent, a decrease in T_g was observed. The storage modulus (E′) followed a similar trend, i.e., E′ increased from 1.3 GPa to 5.2 GPa and 3.4 GPa, upon the addition of NDs and SWNTs. The LCPE‐S showed a lower thermal stability due to the loss of sulfonate groups, i.e. the 5% weight loss temperature (T) is ～280 °C for LCPE‐S vs. 333 °C for LCPE‐R. The decomposition temperature increased somewhat upon addition of the nanoparticles. The ability of dispersing carbon‐based nanostructures combined with an accessible melt processing window makes sulfonated LCPs attractive matrices towards preparing nanocomposites with improved thermal and mechanical properties. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011.     

Pore characterization of assembly-structure controlled single wall carbon nanotube

Single wall carbon nanotube (SWCNT), which has bundle structure and entangled structure, was untangled and cut by sonication in hydrogen peroxide (H₂O₂) solution. The untangled state of SWCNT was examined by SEM, TEM, Raman spectroscopy and N₂ adsorption. It was confirmed that the surface area of sonicated nanotubes strongly depended on the sonication time. The BET specific surface area (SSA) of nanotubes sonicated for 3 h was maximum. The SSA decreased at 6 h or more of sonication time. These results indicated that the bundle structure was untangled and the cap of SWCNT was opened. Thus, N₂ molecules can access the most efficiently inside of the SWCNT sonicated for 3 h. On the contrary, the sonication treatment for 6 h or more decomposed the nanotubes to produce amorphous carbon, evidenced by TEM and SEM observation; the amorphous carbon blocked the open pore sites such as the internal pore spaces and interstitial pores.     

Vertically aligned carbon nanotube based electrodes: Fabrication, characterisation and prospects

We present a methodology to fabricate carbon nanotube based electrodes using plasma enhanced chemical vapour deposition. The metal catalyst nanoparticles used to promote nanotube growth are removed using a water plasma treatment in combination with an acid attack. The final integrated microelectrode-based devices present excellent electrocatalytic properties that make them suitable for electrochemical applications. The presented methodology enables the construction of highly regular and dense vertically aligned carbon nanotube (VACNT) forests that can be confined within the patterned bounds of a desired surface. These VACNT electrodes display very low capacitive currents and are amenable to further chemical modifications.     

The mechanical and electrical properties of carbon nanotube‐grafted polyimide nanocomposites

Polyimide (PI)‐based nanocomposites containing aminophenyl functionalized multiwalled carbon nanotubes (AP‐MWCNTs) obtained through a diazonium salt reaction was successfully prepared by in situ polymerization. PI composites with different loadings of AP‐MWCNTs were fabricated by the thermal conversion of poly(amic acid) (PAA)/AP‐MWCNTs. The mechanical and electrical properties of the AP‐MWCNTs/PI composites were improved compared with those of pure PI due to the homogeneous dispersion of AP‐MWCNTs and the strong interfacial covalent bonds between AP‐MWNTs and the PI matrix. The conductivity of AP‐MWNTs/PI composites (5:95 w/w) was 9.32 × 10^?1 S/cm which was about 10¹⁵ times higher than that of Pure PI. The tensile strength and tensile modules of the AP‐MWCNTs/PI composites with 0.5 wt % of AP‐MWCNTs were increased by about 77% (316.9 ± 10.5 MPa) and 25% (8.30 ± 1.10 GPa) compared to those of pure PI, respectively. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2014 , 52, 960–966     

Elastic modulus of single-walled carbon nanotube/poly(methyl methacrylate) nanocomposites

Dynamic mechanical analysis, nuclear magnetic resonance, and thermogravimetric analysis experiments were performed on pure poly(methyl methacrylate) and on in situ polymerized single-walled carbon nanotube (SWNT)/PMMA nanocomposites. The addition of less than 0.1 wt % SWNT to PMMA led to an increase in the low-temperature elastic modulus of approximately 10% beyond that of pure PMMA. The glass-transition temperature and the elastic modulus at higher temperatures of the nanocomposites remained unchanged from those of pure PMMA. These changes were associated with excessive cohesive interactions between the large-surface area nanotubes and PMMA and were not due to changes in the microstructural features of the polymer during synthesis. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 2286–2293, 2004     

去甲肾上腺素在多壁碳纳米管修饰玻碳电极上的电化学行为

动物体内的去甲肾上腺素(NE)含量变化反映了肢体神经系统植物交感神经的活动状况,在临床和基础研究中非常重要[1-3]。用化学修饰电极研究儿茶酚胺类神经递质的电化学行为以及对其进行测定是目前分析化学比较活跃的研究领域[4-6]。利用羧基化后的多壁碳纳米管(MWC-NT)对电极表面     

Shear piezoelectricity in single‐wall carbon nanotube/poly(γ‐benzyl‐L‐glutamate) composites

Single‐wall carbon nanotubes (SWCNTs) have been added to high molecular weight poly(γ‐benzyl‐L ‐glutamate), or PBLG, to evaluate their effects on the polymer's shear piezoelectricity. While the addition of SWCNTs increased various PBLG physical properties such as electrical conductivity, dielectric constant, several mechanical properties, and electrostriction coefficient, the shear piezoelectricity remained constant up to a 0.3 wt % SWCNT concentration. The composite crystallinity, orientation, and SWCNT alignment (measured by X‐ray diffraction, birefringence, and polarized Raman spectroscopy, respectively) were found to be constant up to this same concentration, corroborating the shear piezoelectric findings. PBLG composites made with acid‐treated (and therefore less electrically conductive) SWCNTs exhibited similar shear piezoelectric behavior, indicating that neither the SWCNT type, concentration (up to the percolation threshold), nor electrical conductivity influences PBLG shear piezoelectricity. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2010     

Facile approach to obtain individual‐nanotube dispersion at high loading in carbon nanotubes/polyimide composites

A big challenge in making a composite lies in achieving individual‐nanotube dispersion of carbon nanotubes (CNTs) in a polymer matrix, without aggregation and entanglement and excellent interfacial adhesion between the CNTs and the polymers matrix. In this communication, using polyethylene glycol‐200, we successfully prepared CNT‐reinforced polyimide composites that exhibit individual‐nanotube dispertion in the matrix at high‐loading CNT's. The content of CNTs in a composite can reach 43 wt%. Copyright © 2007 John Wiley & Sons, Ltd.     

Manufacture and evaluation of carbon nanotube modified screen-printed electrodes as electrochemical tools

Carboxylated multiwalled carbon nanotubes (MWCNT-COOH) dissolved in a mixture of DMF:water were used to modify the surfaces of commercially available screen-printed electrodes (SPEs). The morphology of the MWCNT-COOH and the modified SPEs was characterized by transmission electron microscopy (TEM) and scanning electron microscopy (SEM), respectively. SEM analysis showed a porous structure formed by a film of disordered nanotubes on the surface of the working electrode.The modification procedure with MWCNT-COOH was optimised and it was applied to unify the electrochemical behaviour of different gold and carbon SPEs by using p-aminophenol as the benchmark redox system. The analytical advantages of the MWCNT-COOH-modified SPEs as voltammetric and amperometric detectors as well as their catalytic properties were discussed through the analysis, for instance, of dopamine and hydrogen peroxide. Experimental results show that the electrochemical active area of the nanotube-modified electrode increased around 50%. The repeatability of the modification methodology is around 6% (R.S.D.) and the stability of MWCNT-COOH-modified SPEs is ensured for, at least, 2 months.     

The behavior of benzene confined in a single wall carbon nanotube

We present the molecular dynamics study of benzene molecules confined into the single wall carbon nanotube. The local structure and orientational ordering of benzene molecules are investigated. It is found that the molecules mostly group in the middle distance from the axis of the tube to the wall. The molecules located in the vicinity of the wall demonstrate some deviation from planar shape. There is a tilted orientational ordering of the molecules which depends on the location of the molecule. It is shown that the diffusion coefficient of the benzene molecules is very small at the conditions we report here. © 2015 Wiley Periodicals, Inc.     

Endohedral and exohedral complexes of 1-benzene with carbon nanotubes and high-density assembly of multiple benzenes inside of a carbon nanotube

The 1-benzene was put on the inside and surface of various armchair (n, n) (n = 6-12, 14) and zigzag (n, 0) (n = 10-17, 20) nanotubes of different diameters. The binding structure, binding energy, and effects on binding energy were analyzed. All interaction structures and the properties of the assembled complexes were investigated via density functional tight-binding method. Furthermore, we put multiple benzene molecules (2-18 benzenes) inside the armchair (10, 10), (9, 9), and (8, 8) carbon nanotubes (CNTs) and found that two types of structures were formed for the endohedral complexes of multiple benzenes-spiral symmetrical polygon and criss-crossed types, respectively. The detail of the binding energies and structure properties for (10, 10)/kBen (k = 1-6, 18), (9, 9)/kBen (k = 4, 5, 15), and (8, 8)/kBen (k = 1-8) were discussed. Furthermore, the HOMOs and LUMOs of the representative complexes were also studied to illustrate the interactions. This article offers a new assembly method to prepare a high density of benzenes inside of CNTs and offers a method for benzene adsorption by CNT.     

Magnetorheology of soft magnetic carbonyl iron suspension with single-walled carbon nanotube additive and its yield stress scaling function

The serious dispersion problem of carbonyl iron (CI) based magnetorheological (MR) fluid, due to the large density mismatch between CI particles and continuous medium, has hampered its MR applications. To resolve this undesirable sedimentation, we introduced fibrous single-walled carbon nanotube (SWNT) into CI suspension as additives. The dynamic yield stress change measured as a function of magnetic field strength was examined by adopting a universal equation which was originally applied for electrorheological (ER) fluids. In addition, the viscoelastic performances of CI/SWNT suspension were compared to investigate the influence of additives on the pristine CI suspension. The sedimentation ratio was also examined to confirm the role of submicron SWNT bundles.     

Fabrication and electroactive responsive behavior of shape–memory nanocomposite incorporated with self‐assembled multiwalled carbon nanotube nanopaper

A novel shape–memory nanocomposite that exhibits electrical actuation capabilities was fabricated by incorporating a conductive multiwalled carbon nanotube (MWCNT) nanopaper into shape–memory polymer matrix. The self‐assembled MWCNT nanopaper was made on hydrophilic polycarbonate membrane. This process was based on well‐defined dispersion of the nanosized individual MWCNT and controlled traditional pressure vacuum deposition procedure. The self‐assembled MWCNTs in the nanopaper provided a percolating conductive network with a large interfacial area. It not only offered a high electrical conductivity but also simultaneously enhanced recovery speed by electrically resistive heating, with increasing the content of MWCNT nanopaper in nanocomposite. Copyright © 2011 John Wiley & Sons, Ltd.     

Multifunctional poly(2,5‐benzimidazole)/carbon nanotube composite films

The AB‐monomer, 3,4‐diaminobenzoic acid dihydrochloride, was recrystallized from an aqueous hydrochloric acid solution and used to synthesize high‐molecular‐weight poly(2,5‐benzimidazole) (ABPBI). ABPBI/carbon nanotube (CNT) composites were prepared via in situ polymerization of the AB‐monomer in the presence of single‐walled carbon nanotube (SWCNT) or multiwalled carbon nanotube (MWCNT) in a mildly acidic polyphosphoric acid. The ABPBI/SWCNT and ABPBI/MWCNT composites displayed good solubility in methanesulfonic acid and thus, uniform films could be cast. The morphology of these composite films was studied by X‐ray diffraction, scanning electron microscopy, transmission electron microscopy, and atomic force microscopy. The results showed that both types of CNTs were uniformly dispersed into the ABPBI matrix. Tensile properties of the composite films were significantly improved when compared with ABPBI, and their toughness (～200 MPa) was close to the nature's toughest spider silk (～215 MPa). The electrical conductivities of ABPBI/SWCNT and ABPBI/MWCNT composite films were 9.10 × 10^?5 and 2.53 × 10^?1 S/cm, respectively, whereas that of ABPBI film was 4.81 × 10^?6 S/cm. These values are ～19 and 52,700 times enhanced by the presence of SWCNT and MWCNT, respectively. Finally, without acid impregnation, the ABPBI film was nonconducting while the SWCNT‐ and MWCNT‐based composites were proton conducting with maximum conductivities of 0.018 and 0.017 S/cm, respectively. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 1067–1078, 2010