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)-(2)H(2)O catanionic system forms a large isotropic (L(1)) phase at 25 degrees C. The evolution of microstructure along different dilution lines has been followed by means of rheology and NMR diffusometry. In general, the L(1) phase is characterised by a weak viscoelasticity and Newtonian response. In the STDC-rich regime (W(s)=[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 (C(s)) dependency of both zero-shear viscosity (eta(0) approximately C(s)(3.7)) and surfactant self-diffusion (D(s) approximately C(s)(-3.0)). As the surfactant molar ratio (W(s)1) increases, i.e., DDAB concentration increases, and at constant C(s), eta(0) decreases and D(s) increases, indicating the formation of a multiconnected micellar network.
Youssry
Mohamed
M
Department of Chemistry, University of Calabria, Arcavacata di Rende (CS)-87036, Italy. youssry@unical.it
Coppola
Luigi
L
Marques
Eduardo F
EF
Nicotera
Isabella
I
D001647:Bile Acids and Salts / Q000737:chemistry*; D004058:Diffusion; D009682:Magnetic Resonance Spectroscopy; D008823:Micelles; D000644:Quaternary Ammonium Compounds / Q000737:chemistry*; D012212:Rheology; D012996:Solutions; D013501:Surface-Active Agents; D014783:Viscosity
D001647:Bile Acids and Salts; D008823:Micelles; D000644:Quaternary Ammonium Compounds; D012996:Solutions; D013501:Surface-Active Agents; C046112:didodecyldimethylammonium