Internally gelled w/o and w/o/w double emulsions
Résumé
Water-in-oil emulsions having their aqueous internal phase gelled with starch were prepared and investigated. They were the primary emulsions required
for the preparation of double w/o/w emulsions that could encapsulate hydrophilic materials inside the internal aqueous gel. The emulsification could be achieved at high temperature in spite of the high viscosity of the aqueous phase; the internal phase gelled upon cooling to room temperature. The high viscosity of the aqueous phase limited the possible concentration range of starch in the aqueous phase. The presence of starch made the surfactant demand larger for both the emulsification and the stabilization of the w/o emulsions. The larger the starch content, the larger the amount of required surfactant. One reason for the high surfactant demand was the high viscosity of the aqueous phase containing starch. Another cause of high surfactant demand was disclosed and it appeared that predominantly the
interactions of the nonionic surfactants with starch retained the former inside the
aqueous phase. The immobilized amount of surfactant had to be compensated by a supplementary concentration. Experimental evidence of the interactions between starch and the nonionic surfactants was given by interfacial tension measurements.
Lastly, w/o/w double emulsions were prepared using the gelled w/o emulsions and a model hydrophilic molecule (caffeine) was encapsulated inside the internal gelled
aqueous phase. The release rate of caffeine from the internally gelled double emulsions was slower than for the non-gelled emulsions, demonstrating the
efficiency of the encapsulation and the possible control of the delivery.