We propose an approach to disperse long single-wall carbon nanotubes (SWCNTs) in a manner that is most suitable for the fabrication of high-performance composites. We compare three general classes of dispersion mechanisms, which encompass 11 different dispersion methods, and we have dispersed long SWCNTs, short multi-wall carbon nanotubes, and short SWCNTs in order to understand the most appropriate dispersion methods for the different types of CNTs. From this study, we have found that the turbulent flow methods, as represented by the Nanomizer and high-pressure jet mill methods, produced unique and superior dispersibility of long SWCNTs, which was advantageous for the fabrication of highly conductive composites. The results were interpreted to imply that the biaxial shearing force caused an exfoliation effect to disperse the long SWCNTs homogeneously while suppressing damage. A conceptual model was developed to explain this dispersion mechanism, which is important for future work on advanced CNT composites.
ABSTRACT:The morphology, lateral growth rate and long spacings of isotactic poly(butene-1) (it-PB1) have been investigated for crystallization from the melt over a wide range of crystallization temperature from 50 to 111.9 C. The morphology of it-PB1 crystals is rounded shape at crystallization temperatures lower than 85 C, while lamellar single crystals possess faceted morphology at higher crystallization temperatures; the kinetic roughening transition occurs around 85 C. The nucleation and growth mechanism for crystallization does not work below 85 C, since the growth face is rough. However, the growth rate and the long spacings show the supercooling dependence derived from the nucleation and growth mechanism; the nucleation theory seems still to work even for rough surface growth. Crystallization of polymers has been investigated through morphology, growth rate and lamellar thickness. The growth rate observed at a crystallization temperature, T, is known to be well described by the following equationwhere G 0 and K are constants, U is the 'activation' energy for polymer diffusion, R ¼ kN A , (k is the Boltzmann constant and N A is Avogadro's number)m is the equilibrium melting temperature). The first exponential factor is the VogelFulcher factor for viscosity and the second exponential factor is the surface kinetic factor.According to the nucleation theory 1 by Hoffman et al., the secondary two-dimensional nucleation rate i is given by the following equation:
The morphology, crystalline structure and crystal growth kinetics of melt-crystallized thin isotactic polybutene-1 films have been studied with transmission electron microscopy, electron diffraction and optical microscopy. It is demonstrated that a bypass of tetragonal phase crystallization and direct melt crystal growth of the trigonal phase can be achieved via self-seeding at atmospheric pressure using solution-grown trigonal crystals as nuclei. Electron microscopy and optical microscopy observations show that melt-crystallized isotactic polybutene-1 single crystals of the trigonal phase have rounded or hexagonal morphologies around 75°C. The growth rate of trigonal crystals in the melt has been obtained by in-situ optical microscopy. The growth rate of trigonal crystals in the melt is 1/100 and 1/1000 that of tetragonal crystals in the melt around 70 and 90°C, respectively.
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