GRAFT-COPOLYMERS AS STABILIZERS FOR OIL-IN-WATER EMULSIONS .2. PREPARATION OF THE EMULSIONS AND THE FACTORS AFFECTING THEIR STABILITY

Oil-in-water emulsions were prepared using a series of synthetic graft copolymers with a backbone of poly(methyl methacrylate) and a number of side-chains of poly(ethylene glycol). The properties of such preparations are reported in a separate paper (Part 1 of this communication; A.E. Cardenas-Valera, A.I. Bailey and A. Doroszkowski, Colloids Surfaces A: Physicochem. Eng. Aspects 96(1995)53-57.) The organic phase was toluene, n-heptane or a mixture of the two materials. The emulsions were characterized far mean droplet diameter by means of a laser scattering technique. The stability of the emulsions was monitored as a function of time by the observation of changes in the mean droplet size distribution. Drainage tests were also carried out. The results were correlated with the structure of the molecules, their conformation at the interface, and formulation variables such as the water/oil ratio and surfactant concentration. The results show that stability is enhanced by increasing the thickness and density of the sheath formed around the oil droplet. For copolymers containing a large proportion of the stabilizing moiety (> 40%), the addition of heptane to the organic phase leads to a more stable emulsion. This is due to the reduction of the solvency of the backbone in the oil phase which pushes it towards the plane of the interface, thus achieving better interfacial coverage.