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Carbon nanotubes have long been of interest as additives for increasing the mechanical and electronic properties of polymers, and considerable progress has been made.[1±6] However, melt-phase and solution viscosities ordinarily become too high for conventional processing when the nanotube component exceeds about 10 wt.-%, which limits the nanotube contribution to composite properties. In a groundbreaking development, Vigolo et al. have shown that composite fibers comprising largely nanotubes can be obtained by a process called polyvinyl alcohol (PVA) coagulation spinning. [7±9] In this process, a dilute surfactant-assisted single-walled carbon nanotube (SWNT) dispersion is coagulated into a gel state by spinning it into an aqueous PVA solution; this is followed by conversion into a solid fiber by a slow draw process, during which the water in the gel evaporates. [7±9] We recently reported improvements in this fiber-spinning technique that dramatically increased fiber strength and fiber-spinning rate.[10±12]These improved fibers (comprised of about 60 % SWNTs in a PVA matrix) have a capacity to absorb energy (a specific toughness of about 600 J g ±1 ) that is much higher than any other natural or synthetic organic fiber. Additionally, these SWNT fibers have been successfully utilized in the fabrication of electrochemical devices, such as electromechanical actuators [1,12] and supercapacitors. [10,11] However, unless the polymer is removed by pyrolysis (which degrades the mechanical properties of the fiber), performance of these electrochemical devices is limited by the low electrical conductivity of the nanotube/polymer composite fibers and degradation of mechanical stability when the PVA in these fibers is converted into an ionic conductor. [11] We show here that fibers with useful mechanical properties can be spun if we replace the PVA coagulant with a polyethyleneimine (PEI) coagulant. Although the PEI used is ordinarily a liquid at room temperature, it interacts with the nanotubes to serve as an intertube binding agent. The resulting strain-to-failure and toughness of the PEI-containing fibers are far greater than those of the thermally annealed, binder-free SWNT fibers (which have the advantage of a somewhat higher tensile strength and electrical conductivity) that were spun using the pioneering superacid method developed by the Rice group. [13,14] While the fiber strength and toughness achieved here are far less than those of fibers obtained from the continuous spinning process of Dalton et al. for producing SWNT/PVA composite fibers, [10,11] the prospects of improving the mechanical properties of the SWNT/PEI fibers appear good. Moreover, the electrical conductivity of the SWNT/PEI composite fibers is over a hundred times that of the supertough SWNT/PVA composite fibers. PEI and, in general, amines, are known to effectively interact with carbon nanotubes via physisorption on the nanotubes' sidewalls.[15±21] Thus, a method for separating metallic and semiconducting SWNTs has been developed that uses the hi...

The influence of a compatibilizer on the thermal and dynamic mechanical properties of PEEK/carbon nanotube composites Díez-Pascual, A. M.; Naffakh, M.; Gómez, M. A.; Marco, C.; Ellis, G.; González-Domínguez, J. M.; Ansón, A; Martínez, M. T.; Martínez-Rubi, Y.; Simard, B.; Ashrafi, B. AbstractThe effect of polyetherimide (PEI) as a compatibilizing agent on the morphology, thermal, electrical and dynamic mechanical properties of poly(ether ether ketone) (PEEK)/single-walled carbon nanotube (SWCNT) nanocomposites, has been investigated for different CNT loadings. After a pre-processing step based on ball milling and pre-mixing under mechanical treatment in ethanol, the samples were prepared by melt extrusion. A more homogeneous distribution of the CNTs throughout the matrix is found for composites containing PEI, as revealed by scanning electron microscopy. Thermogravimetric analysis demonstrates an increase in the matrix degradation temperatures under dry air and nitrogen atmospheres with the addition of SWCNTs; the level of thermal stability of these nanocomposites is maintained when PEI is incorporated. Both differential scanning calorimetry and synchrotron x-ray scattering studies indicate a slight decrease in the crystallization temperatures of the compatibilized samples, and suggest the existence of reorganization phenomena during the heating, which are favoured in the composites incorporating the compatibilizer, due to their smaller crystal size. Dynamic mechanical studies show an increase in the glass transition temperature of the nanocomposites upon the addition of PEI. Furthermore, the presence of PEI causes an enhancement in the storage modulus, and hence in the rigidity of these systems, attributed to an improved interfacial adhesion between the reinforcement and the matrix. The electrical and thermal conductivities of these composites decrease with the incorporation of PEI. Overall, the compatibilized samples exhibit improved properties and are promising for their use in industrial applications.

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