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 emulsions 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 preparation) with slow release rates through the liquid oil membrane (60% release after 30 days), were obtained. The halides, with the exception of iodide, showed almost the same typical slow release rates to the outer water phase. The release rates of the ephedrine hydrochloride and KNO₃ were faster than that of the halides. The results suggested that multiple emulsions based on silicone surfactants can be used as slow release systems for agricultural applications. Up to 20 wt% of the total concentration of the hydrophobic silicone-based emulsifier (E₁- the inner emulsifier) was replaced by Span 80. As a result, water was entrapped in the oil phase, suggesting formation of reverse micelles in the presence of Span 80, explaining, in part, the release kinetics of the halides. The release seems to be composed of three separate stages: lag time, fast release and "no release". The release mechanism seems to comply, in part, with a transport mechanism involving "reverse micelles" and is also dependent on the hydrophobicity of the marker. The more hydrophobic markers (the drug and iodide) seem to be released also by "direct diffusion of the molecule through the oil" in addition to their release through the reverse micelles.