ELECTROPHORETIC STUDIES OF CALCIUM-CARBONATE PARTICLES DISPERSED IN VARIOUS HYDROCARBON LIQUIDS

The electrophoretic mobilities for an overbased calcium additive dispersed in a variety of non-polar hydrocarbon media have been determined using phase-analysis light scattering. It is evident that a significant charge exists at the particle/liquid interface, probably as a result of the alkyl benzene sulphonate surfactant being incorporated into the additive. It is apparent that the magnitude of the estimated surface potential when the additive is redispersed into different organic media is initially the same for a given additive. In the case of aliphatic hydrocarbons (cyclohexane and dodecane), the surface potential remains constant with time. However, when aromatic hydrocarbon media are employed, the surface potential decreases with time at a rate that correlates with the molecular size of the hydrocarbon. The effect of the presence of water has been studied and it is found that the mobility of particles dispersed into aromatic media is strongly influenced by the amount of water present. The converse is found for aliphatic media. An additive with shorter surfactant chains is found to exhibit more negative surface potentials in all media compared to an additive with longer surfactant chains. The results are explained in terms of the equilibrium between surfactant at the solid/liquid interface and in free solution.