Water-in-oil gel emulsions from a cholesterol derivative: structure and unusual properties.

As the first example of cholesterol derivatives, butane-1,4-dicarboxamide of di-cholesteryl L-alaninate has been shown to form water-in-oil type gel emulsions. The oils can be n-alkanes (7 < or = n < or = 10) and commercial fuels. Importantly, the preparation of the gel emulsions is a simple agitation process at room temperature, heating, cooling, addition of a co-solvent, or other additional procedures is not necessary. SEM, optical and con-focal laser scanning fluorescence microscopy measurements revealed the foam-like structures of the gel emulsions. Rheological studies demonstrated that these gel emulsions are mechanically stable, and exhibit typical viscoelastic properties. Surprisingly, the storage modulus, G' and the yield stress of the gel emulsions decrease along with increasing the volume ratio of the dispersed phase, water, a property different from the gel emulsions reported in the literatures. From the view point of application, the present gel emulsions are superior to others because of the simplicity in preparation and the non-ionic nature of the emulsifier, which will definitely benefit the practical applications.