Vesiculation of single-chain surfactant mixtures

Abstract

Mixtures of single-chain surfactants usually form micellar aggregates. However, catanionic mixtures exhibit spontaneous reorganization to vesicles under proper conditions. The strong electrostatic interactions of the head-groups cause the formation of a closed-shell bilayer structure. We have synthesized long-chain acylated amino acid salts to study the influences of charge, polarity, size, rigidity, and chirality of the anionic headgroups on the self-assembling processes when being mixed with N-dodecyl pyridinium chloride (DPC). — Vesicles are formed upon gently mixing of the parent micellar solutions. Investigating the whole range of catanionic compositions by light scattering, we could distinguish areas of mixed micellar and unilamellar vesicular aggregates, which were evidenced by various microscopic techniques. — By ¹H-NMR the electrostatic interactions between the cationic DPC and anionic SLS (Sodium N-lauroylsarcosinate) headgroups were found to cause small but significant changes in the chemical shift of the methylene protons adjacent to the carboxyl group. Spin-spin relaxation (T ₂, T ₂⋆) measurements reveal a strong immobilization of the anionic headgroups due to membrane formation. We also found significant changes in the configuration distributions of SLS accompanying the membrane formation in the vesicles. — These findings evidence the importance of configurational and conformational states of the amphiphiles for the micellar-vesicular transformations.