Unravelling micellar structure and dynamics in an unusually extensive DDAB/bile salt catanionic solution by rheology and NMR-diffusometry

The mixed didodecyldimethylammonium bromide (DDAB)–sodium taurodeoxycholate (STDC)–2H2O catanionic system forms a large isotropic (L1) phase at 25 °C. The evolution of microstructure along different dilution lines has been followed by means of rheology and NMR diffusometry. In general, the L1 phase is characterised by a weak viscoelasticity and Newtonian response. In the STDC-rich regime (Ws=[DDAB]/[STDC]=0.2Ws=[DDAB]/[STDC]=0.2), 5 wt% is an overlapping concentration at which the discrete-to-rodlike micellar transition occurs as indicated from the total surfactant concentration (CsCs) dependency of both zero-shear viscosity (η0∼Cs3.7) and surfactant self-diffusion (Ds∼Cs−3.0). As the surfactant molar ratio (Ws⩾1Ws⩾1) increases, i.e., DDAB concentration increases, and at constant CsCs, η0η0 decreases and DsDs increases, indicating the formation of a multiconnected micellar network.

Graphical abstractDiminishing of the viscosity (η0η0) and increasing of the surfactant self-diffusion coefficient (DsDs) are ascribed to the formation of multiconnected micellar induced by DDAB addition.Figure optionsDownload full-size imageDownload as PowerPoint slide