Rates of solubilization of triolein/fatty acid mixtures by nonionic surfactant solutions

Spontaneously-generated convection and rapid initial solubilization were observed when drops containing mixtures of triolein and oleic acid were injected into aqueous solutions of nonionic surfactants. For drops having oleic acid contents between 15% and 25% by weight, solubilization rates were at least an order of magnitude greater than those found for pure triolein, and drop volumes decreased by amounts ranging from 45% to 70% in less than 5 min with no external stirring. With the assumption that the end of the rapid solubilization period occurred because most of the oleic acid had been solubilized, it could be shown that about two thirds by volume of the material solubilized was triolein. At later times the solubilization rate was about the same as that for pure triolein with the same surfactant solutions. A similar effect was observed during the first minute or two after contact for a hydrocarbon/oleic acid mixture. Spontaneously-generated convection and rapid initial solubilization of triolein occurred for only a few seconds when the experiment was conducted at pH 9 or 10. When oleic acid was replaced by lauric acid at neutral pH, there was no convection and no significant enhancement of the rate of triolein solubilization. In this case an intermediate phase containing relatively little triolein developed between the oil and aqueous phases.