Vesicle aggregation based on hydrophobic interactions

Abstract

Vesicles were formed in aqueous mixtures of gemini anionic surfactant, O,O′-bis(sodium 2-alkylcarboxylate)-p-dibenzenediol (referred to as Cmϕ2Cm, m = 10, 12), and single-chain cationic surfactant, alkyltrimethylammonium bromides CnNBr (n = 8, 10, 12). This was confirmed by measurements of solution turbidity, dynamic light scattering (DLS) and freeze-fractured TEM. The improvement of the Cmϕ2Cm molecular geometry by CnNBr was considered to have been due to vesicle formation. As the temperature was raised, these vesicles were found to associate together and DLS measurements showed a rapid increase of the aggregate size at the critical temperature Tc. The mechanism of vesicle aggregation was assumed to be due to the temperature-induced configuration transition of a few Cmϕ2Cm molecules in the vesicles from cis- into trans-form. Thus, a few tails of Cmϕ2Cm stretched toward the solution. When the vesicles approached, these projecting tails interacted hydrophobically, thereby non-covalently attaching one vesicle to another. This should benefit from the special molecular structure of Cmϕ2Cm with a long, rigid spacer.