In general, the phase separation of emulsions prepared with hexadecane was much faster than in the case of the emulsions prepared with soybean oil, mainly at 30:70 W:O ratio, in which the sedimentation index was higher than 40% in less than one day (Fig. 6b). The emulsions with hexadecane and lecithin were the most unstable, since practically instantaneous phase separation was observed. Besides, similarly to the soybean oil emulsion with the same emulsifier, there was aqueous phase separation in the emulsion at 60:40 W:O ratio. The PGPR emulsion with hexadecane at 60:40 W:O ratio showed better stability than the respective system at 30:70, but much worse than the soybean oil systems.
On the other hand, the emulsion prepared with water and hexadecane stabilized by Span 80 at 60:40 W:O ratio showed better kinetic stability than the respective system with soybean oil. After two days of storage, only 0.8% of the hexadecane separated from the emulsion, while in the water–soybean oil system, 8.0% of the oil had already come apart from the emulsion.
In order to understand the stabilization mechanism and the characteristics of each water–oil system formed using different oils and emulsifiers, the structure and viscosity of the emulsions was studied in microscopic and rheological approaches.