Solubilisation of Oils of Different Polarity in Aqueous Solutions of Pluronic Triblock Copolymers

Abstract

Abstract The micellisation behaviour of Pluronic F108 was studied as a function of the addition of various more or less polar additives, such as hexanol, geraniol, toluene, methyl heptanoate, polyproylene oxide (PPO), and nitropropane. It is observed that the critical micellisation temperature (CMT) is substantially reduced upon the solubilisation of most of the additives (but not for methyl heptanoate and PPO) and at the same time the concomitant enthalpy of micellisation becomes larger. Both changes in CMT and enthalpy of micellisation are linear with respect to the concentration of additive. The pronouncedness of this effect is related to the polarity of the additive (as characterised for instance by its water solubility) and for instance similar effects are achieved for much smaller amounts of geraniol compared to hexanol. The structural evolution of the Pluronic solutions upon addition of the additives was also followed by SANS experiments and show that relatively small amounts of added solubilisate can have a very pronounced effect on the extent of the micellisation and size of the aggregates formed, i.e., effectively lowering the CMT by rendering the amphiphilic system more hydrophobic and especially the medium chain alcohols show pronounced synergism.