The differences in surfactant adsorption on carbon nanotubes and their bundles.
ABSTRACT Dissipative particle dynamics simulations of a mesoscale model are performed to investigate the concentration dependence of surfactant adsorption on small-diameter carbon nanotubes and their bundles. Adsorption is found to follow fundamentally different mechanisms in the two cases because of the heterogeneity of the bundle surface and the difference in diameter of bundles compared to that of individual tubes. Whereas aggregation dominates adsorption on individual tubes, on bundles it is largely a Langmuir-type process. High adsorption energy sites on the outer surface of bundles, where surfactant molecules can interact with two tubes simultaneously, dominate at low coverage. They also cause adsorption on bundles to become significant well before adsorption on individual tubes starts. The difference in the adsorption mechanisms leads to a crossover point at higher concentrations, where the adsorbed amount per surface area on individual tubes becomes larger than that for the bundles.
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ABSTRACT: Several series of nanocomposites were prepared using a latex-based process, the main step of which consisted of mixing an aqueous suspension of exfoliated carbon nanotubes (CNTs) and a polymer latex. In the present work, a systematic study on the electrical properties of fully amorphous (polystyrene – PS) as well as semi-crystalline (isotactic polypropylene – iPP) nanocomposites containing either single-wall (SWCNTs) or multi-wall carbon nanotubes (MWCNTs) has been conducted. Percolation thresholds as low as 0.05 wt.% or 0.1 wt.% were observed for SWCNT/iPP and MWCNT/iPP nanocomposites, respectively. The formation of a conductive percolating network at such a low CNT concentration is favored by the high intrinsic conductivity and the low viscosity of the polymer matrix. The electrical percolation threshold of the iPP-based system was found to be lower than its rheological percolation threshold. Beyond the percolation threshold, MWCNT-based nanocomposites generally exhibited higher conductivity levels than those based on SWCNTs, most probably due to the higher intrinsic conductivity of the MWCNTs as compared to that of the SWCNTs. These excellent electrical properties, associated with the strong nucleating effect of the CNTs reported earlier [1,2], render this type of nanocomposites extremely attractive from a technological point of view.European Polymer Journal - EUR POLYM J. 01/2010; 46(9):1833-1843.