Fabrication and properties of composites of

Carbon nanotubes (CNTs) [1, 2] have dimensions similar to those of typical polymeric chains, with 1-50nm in diameter and 1-10µm in length. Experimental results on individual carbon nanotubes and nanotube bundles show that they have exceptional electrical and mechanical properties with an elastic modulus of ~1TPa and fracture strain of 5-10%. [3] The thermal conductivity of the nanotubes is expected to be higher than that of the carbon fibers because of their structural perfection. As a result there are considerable interests in utilization of CNTs as fillers for thermal management and structural reinforcement. Although there have been several published studies on polymer-CNT composites [4-9], realization of the expected enhancement in properties, especially mechanical properties, has by and large not been demonstrated. This is in part because of the difficulties in materials processing arising from insolubility of the pristine CNTs. Recent studies have shown that CNTs can be chemically functionalized such that they are soluble in selected solvents. [10, 11] Mickelson et al. reported that fluorinated SWNTs (F-SWNTs) were dissolved in 2-propanol at a concentration of 1 mg/mL at room temperature. [12] The nanotubes appear to be intact and are electrically insulating after fluorination. The enhanced solubility and potential of tailoring the interfacial bonding between the nanotubes and the matrix by modifying the side-groups make functionalized CNTs attractive fillers for composites. Here we report results from initial studies of composites of F-SWNTs and a semi-crystalline thermoplastic polymer, poly-(ethylene oxide) (PEO). Electron microscopy and thermal analysis showed that they have improved uniformity and nanotube dispersion compared with those by pristine SWNTs. Significant enhancement of the mechanical properties was obtained. The storage modulus (E') and yield strength increased monotonically with increasing F-SWNT loading. At 4wt% loading, the room temperature E' is 400% of that of the control sample. Further analysis indicates strong interfacial bonding between the F-SWNTs and the PEO matrix. 2 Single-walled nanotube bundles (SWNTs) [13] were synthesized by the laser ablation method under conditions described elsewhere. [14] The raw materials were purified to remove the impurity phases such as amorphous carbon and graphitic nanoparticles by reflux in H 2 O 2 followed by filtration. [15] Transmission electron microscopy (TEM) and x-ray diffraction studies show that the samples contain over 90% SWNT bundles with the average bundle diameter of 30-50nm, tube diameter of 1.4nm and bundle length of 5-10µm. For the fluorination reaction, 10-15mg purified SWNTs were dispersed in dimethylformamide (DMF) by …