Effect of pH on adsorption and desorption of clay particles at oil-water interface

Kaolinite clay particles treated with asphaltenes were used to study the effect of pH of the aqueous phase on the clay partitioning between an oil-in-water emulsion and an aqueous phase, Contact angle measurements showed that when the clays were first immersed into oil, the contact angle of the clays was higher than that when the clays were first contacted with water, It was found that both ?he contact angle versus pH curves and the clay coverage at the oil droplet surface versus pH curves exhibited a maximum at pH approximate to 6. Under similar emulsification conditions, higher pH of the aqueous phase resulted in larger diameter of the oil droplets, When the creamed emulsions prepared at pH 7 were redispersed into an aqueous phase having a different pH, the clays desorbed from the oil droplet surface at pH values higher than 6, but further adsorbed onto the oil droplet surface at pH values lower than 6. (C) 1996 Academic Press, Inc.