Structures and dynamics of carbon-black in suspension probed by static and dynamic ultrasound scattering techniques

Carbon black (CB) suspension exhibits various structures depending on the properties of solvent and dispersant as well as the preparation process of suspension. In most cases, CB particles do not exist as independent nanoparticles but as aggregates or agglomerates. In order to evaluate the size distribution at different level of hierarchal structure, we carried out static/dynamic ultrasound scattering analysis for the CB suspensions in alcohol and/or water with or without Nafion, a perfluorinated polymer. The potential of the dynamic ultrasound scattering technique was demonstrated by discriminating diffusing nanoparticles and micron-sized aggregates/agglomerates without dilution of the sample. Particularly, suppression of large agglomerates by addition of Nafion was clearly observed. Phosphotungstic acid (PWA), a family of polyoxometalate, was also employed to obtain smaller unit structures of the CB particles without formation of aggregation after decomposition of CB. The possible structures of the CB/PWA suspensions with and without Nafion were also discussed.