Magnetic anisotropy in the films of oriented carbon nanotubes filled with iron nanoparticles

Films of carbon nanotubes oriented perpendicularly to the substrate surface and filled with iron nanoparticles have been synthesized and studied. Morphological features of these nanocomposite films lead to the appearance of an easy magnetization axis, which is perpendicular to the film plane. A method for enhancement of this effect is suggested and successfully tested.     

Minimizing purification-induced defects in single-walled carbon nanotubes gives films with improved conductivity

A method for the non-destructive purification of single-walled carbon nanotubes (SWNTs) using classical coordination chemistry to remove the metal catalyst has been developed. In preliminary tests, the conductivity of films based on the resulting SWNTs was markedly better than that of films prepared from SWNTs purified by treatment with oxidizing acid solutions. The transparent and conducting SWNT films have potential applications in optoelectronic devices.     

Fracture toughness and electrical conductivity of epoxy composites filled with carbon nanotubes and spherical particles

The attainment of both high toughness and superior electrical conductivity of epoxy composites is a crucial requirement in some engineering applications. Herein, we developed a strategy to improve these performances of epoxy by combining the multi-wall carbon nanotubes (MWCNTs) and spherical particles. Two different types of spherical particles i.e. soft submicron-rubber and rigid nano-silica particles were chosen to modify the epoxy/MWCNT composites. Compared with the binary composites with single-phase particles, the ternary composites with MWCNTs and spherical particles offer a good balance in glass transition temperature, electrical conductivity, stiffness and strength, as well as fracture toughness, exhibiting capacities in tailoring the electrical and mechanical properties of epoxy composites. Based on the fracture surface analysis, the complicated interactions between multiscale particles and the relative toughening mechanisms were evaluated to explain the enhancement in fracture toughness of the ternary composites.     

Molecular interaction and properties of poly(ether ether ketone)/liquid crystalline polymer blends incorporated with functionalized carbon nanotubes

Multi-walled carbon nanotubes (MWCNTs) were functionalized with a carboxyl group (-COOH) to achieve better interfacial adhesions with both phases of the poly(ether ether ketone) (PEEK) and liquid crystalline polymer (LCP) in their blend. These strong interfacial interactions among the functionalized MWCNTs, PEEK and LCP improved the mechanical properties of the polymer blend. Three different weight percentages (0.6%, 1.2% and 1.8%) of acid modified CNTs were used with PEEK-LCP blend, for the preparation of nanocomposites. In PEEK-LCP blend, the ratio of PEEK and LCP was maintained as 10:6 respectively. The tensile strength and modulus of the composites were improved by 51% and 73% respectively with the incorporation of only 1.2% of MWCNT-COOH as compared to the unfilled PEEK/LCP blend. Moreover, careful studies of the molecular interaction, morphological, dynamic mechanical and thermal properties confirmed that a better miscibility between PEEK and LCP had been constituted in the presence of MWCNT-COOH. Therefore, it was found that the functionalized MWCNTs not only played the traditional role as reinforcing filler, but also performed a novel role as a compatibilizer for the PEEK/LCP blends.     

Optical transmission of polymer dispersed liquid crystals doped with carbon nanotubes

The optical transmission of polymer-dispersed liquid crystals (PDLCs) doped with multiwall carbon nanotubes (MWNTs) has been studied in comparison to the analogous system without MWNTs. The transmission of MWNT-doped PDLC cells in crossed polarizers exhibits an anomalous dependence on the control voltage. The anomalous behavior is attributed to a preliminary partial orientation of molecules in the presence of carbon nanotubes in the dispersed liquid crystal droplets.     

Thermal conductivity of filled polymer compositions

An equation for calculating the thermal conductivity of filled polymer compositions is derived and confirmed experimentally.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 41, No. 3, pp. 483–490, September, 1981.     

纳米碳管内包覆外来物质的研究进展

纳米碳管具有纳米尺度的准一维中空结构,这使得在其中空管腔内填充外来物质成为可能。填充纳米碳管的理化性能与填充物的种类、结构、组分密切相关,因而人们可以根据需要自主设计和组装各种类型的填充纳米碳管。通过综述目前在纳米碳管内填充外来物质领域的研究动态,介绍填充预先制备的纳米碳管和在制备纳米碳管的过程中同时包覆外来物质的各种物理和化学制备方法及其可能的微观机制,阐述了这类被填充的纳米碳管在电子工业、信息技术、生物化学以及医学等领域的应用前景,并对今后尚待开展的纳米碳管与填充物质的相互作用规律、这种量子线的物理性能及其阵列的制备技术等研究工作进行了探讨和展望。     

Realization of porous poly(methyl methacrylate) films filled with electrodeposited carbon nanotubes

A deposition process on a conducting surface, in which water acted as the dispersed phase and a mixture of poly(methyl methacrylate) and chloroform as the continuous phase, was applied to prepare poly(methyl methacrylate) films. The influence of relative humidity during the film preparation on the surface morphology was investigated by field emission scanning microscopy. High-humidity preparation conditions lead to porous poly(methyl methacrylate) films. These films were then used as templates to perform the selective deposition into the pores of single-walled carbon nanotubes by an electrophoretic method. The attractive properties of carbon nanotubes combined with the versatile properties of poly(methyl methacrylate) open up new opportunities for these nanocomposites to achieve novel architectures in nanodevices and?microdevices.     

Electrical conductivity and Raman imaging of double wall carbon nanotubes in a polymer matrix

Raman spectroscopy is used to access the dispersion state of DWNTs in a PEEK polymer matrix. The interaction of the outer tube with the matrix can be determined from the line shape of the Raman G band. This allows us to distinguish regions where the nanotubes are well dispersed and regions where the nanotubes are agglomerated. The percolation threshold of the electrical conductivity of the double wall carbon nanotubes (DWNTs)/PEEK nanocomposites is found to be at 0.2-0.3 wt%. We find a maximum electrical conductivity of 3 × 10⁻² S cm⁻¹ at 2 wt% loading. We detect nanotube weight concentrations as low as 0.16 wt% by Raman spectroscopy using a yellow excitation wavelength. We compare the Raman images with transmission electron microscopy images and electrical conductivity measurements. A statistical method is used to find a quantitative measure of the DWNTs dispersion in the polymer matrix from the Raman images.     

Magnetic orientation of single-walled carbon nanotubes or their composites using polymer wrapping

Abstract

The magnetic orientation of single-walled carbon nanotubes (SWNTs) or the SWNT composites wrapped with polymer using poly[2-methoxy-5-(2′-ethylhexyloxy)-1,4-phenylene vinylene] (MEHPPV) as the conducting polymer were examined. The formation of SWNT/MEHPPV composites was confirmed by examining absorption and fluorescence spectra. The N,N-dimethylformamide solution of SWNT/MEHPPV composites or the aqueous solution of the shortened SWNTs was introduced dropwise onto a mica or glass plate. The magnetic processing of the composites or the SWNTs was carried out using a superconducting magnet with a horizontal direction (8 T). The AFM images indicated that the SWNT/MEHPPV composites or the SWNTs were oriented randomly without magnetic processing, while with magnetic processing (8 T), they were oriented with the tube axis of the composites or the SWNTs parallel to the magnetic field. In polarized absorption spectra of SWNT/MEHPPV composites on glass plates without magnetic processing, the absorbance due to semiconducting SWNT in the near-IR region in horizontal polarized light was almost the same as that in vertical polarized light. In contrast, with magnetic processing (8 T), the absorbance due to semiconducting SWNT in the horizontal polarization direction against the direction of magnetic field was stronger than that in the vertical polarization direction. Similar results were obtained from the polarized absorption spectra for the shortened SWNTs. These results of polarized absorption spectra also support the magnetic orientation of the SWNT/MEHPPV composites or the SWNTs. On the basis of a comparison of the composites and the SWNTs alone, the magnetic orientation of SWNT/MEHPPV composites is most likely ascribable to the anisotropy in susceptibilities of SWNTs.     

Droplet orientation and optical properties of polymer dispersed liquid crystal composite films

The electro-optic and thermo-optic properties of polymer dispersed liquid crystal (PDLC) films have been investigated. The effects of applied voltage and temperature on liquid crystal droplet morphology and its transmission characteristics were studied. Threshold voltage (V_th) and optical transmission increases with increasing temperature. It may be due to the reduction in effective voltage drop across the liquid crystal droplets in the composite matrix. The liquid crystal droplet size was found to vary in the range of 5–28 μm.     

Flexible and high thermal conductivity thin films based on polymer: Aminated multi-walled carbon nanotubes/micro-aluminum nitride hybrid composites

Multi-walled carbon nanotubes functionalized with amino groups (MWCNT-NH₂) were prepared via the chemical modification of the carboxyl groups introduced on the surface of MWCNT. The synthesized materials and untreated micro-aluminum nitride (micro-AlN) particles were embedded in a polymer resin, viz. epoxy-terminated dimethyl siloxane. The thermal diffusivity and conductivity of all of the composites continuously improved with increasing the content of fillers. A thermal conductivity of 3.81 W/mK was achieved at an MWCNT-NH₂ loading of 3 wt% and micro-AlN loading of 70 wt% while their flexibility was maintained. This result is due to the high aspect ratio of the MWCNT-NH₂ which allows a heat conductive percolation network to be established between the micro-AlN particles. Also, all of the composites fabricated by the optimized process endured about 200,000 bending cycles without rupturing or losing their thermal conductivity.     

Magnetic properties of carbon nanotubes filled with ferromagnetic metals

Carbon nanotubes (CNTs) encapsulating Fe nanowires were prepared by the chemical vapor deposition (CVD) method using ferrocene as a precursor. The influence of the addition of Pt to an Fe catalyst, which is required for growing CNTs by CVD, on the magnetic properties of the resulting CNTs was examined from the viewpoint of enhancing coercivity. Our results showed that the addition of a Pt layer on the Fe catalyst deposited on a substrate increased the coercivity of the Fe-filled CNT. This increase is due to changes in the easy magnetization axis of the Fe nanowires in the CNTs. This result indicates that the magnetic properties of the Fe-filled CNTs can be tuned by the controlling the growth conditions, which is suitable for applications in areas such as magnetic recording media and medicine.     

Thermal conductivity of polymer composites based on the length of multi-walled carbon nanotubes

The anisotropic development of thermal conductivity in polymer composites was evaluated by measuring the isotropic, in-plane and through-plane thermal conductivities of composites containing length-adjusted short and long multi-walled CNTs (MWCNTs). The thermal conductivities of the composites were relatively low irrespective of the MWCNT length due to their high contact resistance and high interfacial resistance to polymer resins, considering the high thermal conductivity of MWCNTs. The isotropic and in-plane thermal conductivities of long-MWCNT-based composites were higher than those of short-MWCNT-based ones and the trend can accurately be calculated using the modified Mori-Tanaka theory. The in-plane thermal conductivity of composites with 2 wt% long MWCNTs was increased to 1.27 W/m·K. The length of MWCNTs in polymer composites is an important physical factor in determining the anisotropic thermal conductivity and must be considered for theoretical simulations. The thermal conductivity of MWCNT polymer composites can be effectively controlled in the processing direction by adjusting the length of the MWCNT filler.     

Effect of polyphosphazene and modified carbon nanotubes on the morphological and thermo-mechanical properties of polyphenylene sulfide and liquid crystalline polymer blend system

Ternary blends of polyphenylene sulfide (PPS) and liquid crystalline polymer (LCP) with either polyphosphazene, unmodified multiwall carbon nanotubes (MWCNTs) or SiC-coated MWCNTs, were prepared by melt blending. While polyphosphazene improved the compatibility between the PPS and LCP, unmodified MWCNTs promoted LCP domain deformation, from spherical to ellipsoidal. Long LCP fibers were formed in presence of SiC-coated MWCNTs due to the bridging effect of modified MWCNTs at the interface of PPS and LCP. This bridging effect was confirmed by field emission scanning electron microscopy (FESEM). The better dispersion of SiC-coated MWCNTs was confirmed by both FESEM and transmission electron microscopy analysis. The superior mechanical properties of SiC-coated MWCNTs added blend system can be attributed to the fibrillation of LCP and better dispersion of SiC-coated MWCNTs. Polyphosphazene containing blend system showed lowest thermal stability while blend with SiC-coated MWCNTs was found to be highest, among all the blend systems.     

Enhancing thermal conductivity of glass fiber/polymer composites through carbon nanotubes incorporation

Carbon nanotubes were effectively incorporated into low-viscosity polyester/vinyl ester resins and then used for infusion of glass fiber textiles by high-pressure injection, resulting in carbon nanotubes/glass fiber/polymer multiscale composites. The nanotubes distribution in the composites was examined by measuring the local density of as-produced composites. The uniformity of local density and scanning electron microscope characterization verified the homogeneous morphology of as-produced composites. Both theoretical calculation and experimental characterization indicated thermal conductivity was significantly improved. Incorporation of 3 wt% carbon nanotubes has resulted in 1.5-folds enhancement of thermal conductivity. These results will further increase industrial application of the fiber composites.     

Thermal conductivity of liquid hydrogen filled foam

The effective thermal conductivities of silica aerogel foam [0.1(10)⁻³ kg m⁻³ nominal density] filled with liquid n-H₂, liquid n-D₂ and an equimolar mixture of liquid H₂D₂ were measured near 19.6 K. Our measured value of 97 mW m⁻¹ K⁻¹ for hydrogen filled foam is essentially the same as for the liquid alone. This result agrees with predictions for the thermal conductivity of porous systems which give a 2% enhancement in the effective thermal conductivity for this system relative to the liquid alone.     

Charge transfer in single-walled carbon nanotubes filled with cadmium halogenides

In this work the internal channels of the single-walled carbon nanotubes (SWCNTs) were filled with cadmium chloride, cadmium bromide, and cadmium iodide by a capillary method using melts of these salts. The influence of incorporated chemical compounds on the electronic properties of the carbon nanotubes was investigated by optical absorption spectroscopy, Raman spectroscopy, near edge X-ray absorption fine structure spectroscopy, and X-ray photoelectron spectroscopy. It was found that there is the chemical bonding between carbon atoms of nanotube walls and metal atoms of encapsulated CdX₂ nanocrystals. The obtained data testify acceptor doping effect of cadmium halogenides incorporated into the SWCNT channels, which is accompanied by the charge transfer from nanotube walls to introduced substances.     

Reinforcing polymer composites with epoxide-grafted carbon nanotubes

An in situ functionalization method was used to graft epoxide onto single-walled carbon nanotubes (SWNTs) and improve the integration of SWNTs into epoxy polymer. The characterization results of Raman, FT-IR and transmission electron microscopy (TEM) validated the successful functionalization with epoxide. These functionalized SWNTs were used to fabricate nanocomposites, resulting in uniform dispersion and strong interfacial bonding. The mechanical test demonstrated that, with only 1?wt% loading of functionalized SWNTs, the tensile strength of nanocomposites was improved by 40%, and Young's modulus by 60%.These results suggested that efficient load transfer has been achieved through epoxide-grafting. This investigation provided an efficient way to improve the interfacial bonding of multifunctional high-performance nanocomposites for lightweight structure material applications.