Alkyltrimethylammonium bromide-induced aggregate transition of carboxylate gemini surfactant with a p-dibenzenediol spacer from networks to thread-like micelles to vesicles

Abstract

The gemini surfactants, O,O’-bis(sodium 2-dodecyl-carboxylate)-p-dibenzenediol and O,O’-bis(sodium 2-decylcarboxylate)-p-dibenzenediol (denoted as C₁₂ϕ₂C₁₂ and C₁₀ϕ₂C₁₀, respectively), were previously found to form network-like aggregates in very dilute solution. In the present work, the effect of alkyltrimethylammonium bromides, C_nNBr, on the network-like aggregates formed by C₁₂ϕ₂C₁₂ and C₁₀ϕ₂C₁₀ was studied using dynamic light scattering, fluorescence probing, steady-state or frequency sweep rheology, and freeze-fractured TEM measurements. These network-like aggregates were easily transformed into core-shell micelles as C_nNBr was added, including spherical micelles and even thread-like micelles, upon increased concentration of C_nNBr. On further increasing C_nNBr concentration, vesicles were formed. The phase diagrams of aggregate transition were plotted. All of these were attributed to the improvement of added C_nNBr on the effective molecule geometry under the base of original columnar-like molecules of C₁₂ϕ₂C₁₂/C₁₀ϕ₂C₁₀.