The self-assembly of C22-tailed surfactants in ethanol (a common solvent favoured for both the alkyl tail and the head-group) induced by the addition of water (a non-solvent for the tail) has been studied using light-scattering measurements. These surfactants self-associated into core-shell micelles in ethanol upon the addition of water. However, the coronas of the micelles cannot envelop the cores particularly well since the cores were swollen by the solvent: these micelles were thereby further associated into secondary aggregates with an average radius of greater than 100 nm. Upon an increase in water content, the core contracted and the exposure of the alkyl tails was lessened: this reduced the extent of secondary aggregation. The surfactant with a more hydrophilic head-group promised the addition of more water. If the water content was relatively high, secondary aggregation may be avoided and complete core-shell micelles could be obtained upon the addition of some additives that filled the gaps in the corona. The results represented the development of a new self-assembly approach to traditional surfactants, by which the solubility thereof was enhanced owing to the use of a common solvent. Therefore, the self-assembly of those surfactants insoluble in water could be examined by this method.
Zhao, Jianxi, Xinzhi Xu, Wenjing Dong, Hongbin Yu
Colloids and Surfaces A: Physicochemical and Engineering Aspects