Homogeneous dispersion of the surface modified MWNTs in the PU matrix and electrical conductivity of the MWNTs/PU composites

Dispersion characteristics of the surface modified MWNTs (Miltiwalled nanotubes) in the PU (polyurethane) matrix and electrical conductivity of the MWNTs/PU composites are investigated using SEM and DEA (Dielectric analyzer) with respect to the chemical treatment of MWNTs, the kind of surfactants and their content. Several chemical treatments of the MWNTs' surfaces were performed with the acids type, acidic concentration, treatment temperature, and oxidation time. All the surface of modified MWNTs are negatively charged and functionalized with carboxylic group; however, the external walls of some MWNTs were severely damaged so that they were frequently thinned and partially cracked. Compared to those of the composites without the addition of surfactant, the surfactant embedded into composites show much better dispersion of the MWNTs and higher electrical conductivity, these results are in good agreement with the two step adsorption model of cationic surfactants proposed by Y. Gao. Both the optimized MWNTs and cationic surfactant filled PU composites show very low percolation threshold, p_c = 0.0089± 0.007 vol. %, and relatively higher conductivity after percolation than other carbon nanotubes composite systems reported elsewhere.