Effect of trace impurities in triglyceride oils on phase inversion of Pickering emulsions stabilized by CaCO3 nanoparticles

It is known that with alkane or toluene as oil, Pickering emulsions stabilized by unmodified CaCO3 nanoparticles are of the oil-in-water (O/W) type. In contrast, when a triglyceride oil such as refined soybean oil or commercial olive oil is used, emulsions stabilized by the same particles are of the water-in-oil (W/O) type. However, if these natural oils are first columned through alumina, O/W emulsions are stabilized as they are with the pure triglyceride tricaprylin. Since we have shown that unmodified CaCO3 nanoparticles can be hydrophobized in situ by trace amounts of anionic surfactant such as sodium dodecyl sulfate or sodium carboxylates present in the aqueous phase, it is suggested that an impurity present in refined soybean oil and commercial olive oil has a similar effect. By using complementary experiments including analyzing the structure of the impurities adsorbed by alumina and adding trace amounts of these impurities into the columned oils, we demonstrate that fatty acid impurity present in the unpurified oils is responsible for the hydrophobization of CaCO3 nanoparticles and the O/W → W/O phase inversion of emulsions.