Microcalorimetric studies of the interaction between DDAB and SDS and the phase behavior of the mixture

The interaction enthalpies between didodecyldimethylammonium bromide (DDAB) and sodium dodecyl sulfate (SDS) have been measured at 298.15 K using an isothermal titration microcalorimeter. From the variation of enthalpy with SDS concentration, the enthalpy of interaction between DDAB micelles and SDS, the enthalpy of formation of the DDA(+)SD(-)(cryst), the enthalpy of vesicle formation of DDAB -SDS, and the enthalpy of transition from-vesicles to SDS-rich micelles have been determined to be -29.53, -125.8, 41.23, and 32.10 kJ/mol, respectively. The phase behavior of the DDAB-SDS aqueous mixture has also been investigated by turbidity measurements and transmission electron microscopy.