We apply the self consistent field (SCF) theory for chain molecules in inhomogeneous systems, originated by Scheutjens and 1, l eer. t o study the interaction between Iwo water droplets in oil in the presence of surfactants . The modelling of interacting polymer-covered rigid interfaces is the classical application in the SCF approach . In this paper we study two surfactant-covered liquid-liquid interfaces near contact . This can he done by an osmotic pressure 'experiment'.
Our analysis indicates that for (surfactant-stabilised) water-in-oil emulsions two types of colloidal instability can be distinguished: (1) coalescence (flocculation in the primary minimum leading to a reduction of the number of droplets) and ( 2) aggregation (flocculation in secondary minimum . formation of clusters of droplets, i .e . a reduction of the number of kinetically active droplets but retaining their individuality) . The surfactant adsorbed at the water oil interface influences these two types of instabilities it) different ways . A high surfactant concentration effectively protects against coalescence, whereas, especially when the molecular weight of the oil molecules is larger than that of the surfactants. aggregation is promoted . Analysis of the interaction curves for lamellar interfaces enables the prediction of the macroscopic contact angle between two droplets . We show that this angle can vary strongly with the type of oil used . Protection against aggregation can be obtained by carefully choosing the surfactant in connection with the oil used .