Surface Properties and Aggregates in the Mixed Systems of Bolaamphiphiles and Their Oppositely Charged Conventional Surfactants

Abstract

Two transition points were observed in the surface tension curves of the mixed systems of cationic bolaamphiphile BPHTAB (biphenyl-4,4‘-bis(oxyhexamethylenetrimethylammonium bromide)) and its oppositely charged conventional surfactants. Transmission electron microscopy, dynamic light scattering, and isothermal titration microcalorimetric experiments demonstrated that spherical vesicles or elongated aggregates formed at the lower surfactant concentration than the corresponding critical micelle concentration (cmc), which led to the existence of two transition points in surface tension curves. Addition of 10% formamide into the mixed system broke the vesicles and elongated aggregates and made the first breaking point disappear. The biphenyl group in the BPHTAB molecule and the appropriate attractive interaction between the cationic and anionic headgroups of the surfactants had a great influence on the ability of vesicle formation and determined whether the two transition points would exist in the surface tension curve.