Effect of Water on Flocculation of Carbon Black in Nonaqueous Surfactant Solutions

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Abstract
The effect of solubilized water on stability or flocculation of four kinds of carbon blacks dispersed in cyclohexane solutions of anionic (AOT) or nonionic (NP-8) surfactants was studied. The stable region (A) appeared at the lower concentration range of water. The stability decreased with increasing concentration of water. An additional increase of water concentration caused marked flocculation (region B) followed by the apparent stable dispersion (region C). The stability of the region A and the transient region to B was elucidated by the interaction of the electric double layers for AOT systems. The flocculation at B may be due to increase of interfacial tension because of the water layer formed on carbon-black particles. The apparent stability of the region C is considered to result from the network structure formed among carbon particles and water-in-oil micro-emulsion particles for AOT systems. This was suggested from shear rate-stress curves. The appearance of the region C for NP-8 systems is considered to be caused by the viscosity (lamellar structure) of the solution.