Highly oriented, large area continuous composite nanofiber sheets made from surface-oxidized multiwalled carbon nanotubes (MWNTs) and polyacrylonitrile (PAN) were successfully developed using electrospinning. The preferred orientation of surface-oxidized MWNTs along the fiber axis was determined with transmission electron microscopy and electron diffraction. The surface morphology and height profile of the composite nanofibers were also investigated using an atomic force microscope in tapping mode. For the first time, it was observed that the orientation of the carbon nanotubes within the nanofibers was much higher than that of the PAN polymer crystal matrix as detected by two-dimensional wide-angle X-ray diffraction experiments. This suggests that not only surface tension and jet elongation but also the slow relaxation of the carbon nanotubes in the nanofibers are determining factors in the orientation of carbon nanotubes. The extensive fine absorption structure detected via UV/vis spectroscopy indicated that charge-transfer complexes formed between the surface-oxidized nanotubes and negatively charged (-CN[triple bond]N:) functional groups in PAN during electrospinning, leading to a strong interfacial bonding between the nanotubes and surrounding polymer chains. As a result of the highly anisotropic orientation and the formation of complexes, the composite nanofiber sheets possessed enhanced electrical conductivity, mechanical properties, thermal deformation temperature, thermal stability, and dimensional stability. The electrical conductivity of the PAN/MWNT composite nanofibers containing 20 wt % nanotubes was enhanced to approximately 1 S/cm. The tensile modulus values of the compressed composite nanofiber sheets were improved significantly to 10.9 and 14.5 GPa along the fiber winding direction at the MWNT loading of 10 and 20 wt %, respectively. The thermal deformation temperature increased with increased MWNT loading. The thermal expansion coefficient of the composite nanofiber sheets was also reduced by more than an order of magnitude to 13 x 10(-6)/ degrees C along the axis of aligned nanofibers containing 20 wt % MWNTs.

Pyrene and 2,7-disubstituted pyrenes have been oxidized with ruthenium(III) chloride (RuCl3) and sodium periodate (NaIO4) under very mild conditions to 4,5-diones or 4,5,9,10-tetraones. Thus, the oxidation has been controlled by varying the amount of oxidant and reaction temperature to proceed exclusively at the pyrene 4- and 5-positions or at the 4-, 5-, 9-, and 10-positions.

We have investigated the self-assembly behavior of an amphiphilic diblock copolymer, polystyrene-block-poly(ethylene oxide) (PS-b-PEO), in N,N-dimethylformamide (DMF)/water and DMF/acetonitrile. In both cases water and acetonitrile are selective solvents for the PEO block. The degrees of polymerization of the PS and PEO blocks were 962 and 227 (PS962-b-PEO227), respectively. Micelle morphologies of the block copolymer in both systems could be controlled by varying copolymer and selective solvent concentrations. With increasing the water concentration in the DMF/water or the acetonitrile concentration in the DMF/acetonitrile system, the micelle morphology observed in transmission electron microscopy changed from spheres to wormlike cylinders and then to vesicles. The morphological diagrams were constructed from the study of the micelle morphology changes in different copolymer concentrations and the critical micellization concentrations for both systems at different copolymer concentrations as determined by static light scattering experiments. In between the concentration regions of two neighboring pure micelle morphologies, mixed morphologies such as spheres with short cylinders or wormlike cylinders with vesicles could be found. Although the trend in morphological changes was identical in these two systems, there were remarkable differences in the morphological diagrams of PS962-b-PEO227 with respect to the percentage of selective solvent added. This is due to the large difference between the polymer-selective solvent interaction parameters. On the basis of the observations of morphological reversibility and annealing experiments, these two morphological diagrams were proven to be in thermodynamic equilibrium. The driving force for these morphological changes was understood to approach micelle free energy minimization. Approximate micelle free energy calculations confirmed that the free energy decreases as the morphology changes from spheres to wormlike cylinders and then to vesicles with an increase in the selective solvent concentrations. Possible change mechanisms are also discussed.