Inhomogeneous Distribution of Cationic Surfactants around Anionic Molecular Clusters.

An interesting phenomenon is reported when uranyl peroxide nanoclusters U (Li K (OH) [UO (O )(OH)] (H O) , m≈20 and n≈310) interact with a small number of cationic surfactant molecules. Cationic surfactant molecules do not distribute evenly around the U clusters during the interaction as expected. Instead, a small fraction of U clusters attract almost all the surfactant molecules, leading to the self-assembly into supramolecular structures by using surfactant-U complexes as building locks, and later further aggregate and precipitate based on hydrophobic interaction, whereas the rest of the clusters remained unbounded soluble macroions in bulk dispersion. This phenomenon nicely demonstrates a unique feature of macroion solutions. Considering that Debye-Hückel approximation is no longer valid in such solutions, the competition between the local electrostatic interaction and hydrophobic interaction becomes important to regulate the solution behaviors of macroions.