Ae. Cardenasvalera et Ai. Bailey, GRAFT-COPOLYMERS AS STABILIZERS FOR OIL-IN-WATER EMULSIONS .2. PREPARATION OF THE EMULSIONS AND THE FACTORS AFFECTING THEIR STABILITY, Colloids and surfaces. A, Physicochemical and engineering aspects, 97(1), 1995, pp. 1-12
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 prepar
ations are reported in a separate paper (Part 1 of this communication;
A.E. Cardenas-Valera, A.I. Bailey and A. Doroszkowski, Colloids Surfa
ces A: Physicochem. Eng. Aspects 96(1995)53-57.) The organic phase was
toluene, n-heptane or a mixture of the two materials. The emulsions w
ere characterized far mean droplet diameter by means of a laser scatte
ring technique. The stability of the emulsions was monitored as a func
tion of time by the observation of changes in the mean droplet size di
stribution. Drainage tests were also carried out. The results were cor
related 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 th
e oil droplet. For copolymers containing a large proportion of the sta
bilizing moiety (> 40%), the addition of heptane to the organic phase
leads to a more stable emulsion. This is due to the reduction of the s
olvency of the backbone in the oil phase which pushes it towards the p
lane of the interface, thus achieving better interfacial coverage.