RELEASE OF MARKERS FROM THE INNER WATER PHASE OF W O/W EMULSIONS STABILIZED BY SILICONE-BASED POLYMERIC SURFACTANTS/

Silicone based surfactants were used as stabilizers for W/O/W double e mulsions with unusual mechanical stability. W/O/ W multiple emulsions containing several markers were prepared. The entrapped markers were: (1) halide salts, (2) a typical drug, ephedrine hydrochloride, and (3) KNO3 (water soluble fertilizer). Good solute trapping (95% yield of p reparation) with slow release rates through the liquid oil membrane (6 0% release after 30 days), were obtained. The halides, with the except ion of iodide, showed almost the same typical slow release rates to th e outer water phase. The release rates of the ephedrine hydrochloride and KNO3 were faster than that of the halides. The results suggested t hat multiple emulsions based on silicone surfactants can be used as sl ow release systems for agricultural applications. Up to 20 wt% of the total concentration of the hydrophobic silicone-based emulsifier (E(1) - the inner emulsifier) was replaced by Span 80. As a result, water w as entrapped in the oil phase, suggesting formation of reverse micelle s in the presence of Span 80, explaining, in part, the release kinetic s of the halides. The release seems to be composed of three separate s tages: lag time, fast release and ''no release''. The release mechanis m seems to comply, in part, with a transport mechanism involving ''rev erse micelles'' and is also dependent on the hydrophobicity of the mar ker. The more hydrophobic markers (the drug and iodide) seem to be rel eased also by ''direct diffusion of the molecule through the oil'' in addition to their release through the reverse micelles.