Abstract
The effect of anionic and cationic surfactants on the separation of a dispersion of a model oil in water is experimentally investigated. As expected, the presence of an anionic or cationic surfactant alone always increases the separation time. However, mixing a dispersion containing an anionic surfactant with a dispersion containing a cationic surfactant significantly reduces the separation time. In both cases the hydrocarbon chain is present in the oil phase with the charged hydrophilic head at the interface in the water phase. The attractive force between the oil drops containing the negatively charged anionic surfactant and the oil drops containing the positively charged cationic surfactant leads to rapid coalescence and separation of the oil in water dispersion. The concentration of the anionic and cationic surfactants are chosen to give the same separation time with identical sedimentation and coalescence profiles. A separation time of 350 s is obtained for a model oil dispersed in water. This time is significantly increased when the dispersion contained an anionic surfactant alone or a cationic surfactant alone. However, mixing these two dispersions reduced the separation time to less than half that for the pure system.
Published Version
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