Study of sodium dodecyl sulfate - Poly(propylene oxide) methacrylate mixed micelles
Résumé
Sodium dodecyl sulfate (SDS) - poly(propylene oxide) methacrylate (PPOMA) (of molecular weight Mw = 434 g·mol-1) mixtures have been studied using conductimetry, static light scattering, fluorescence spectroscopy, and 1H NMR. It has been shown that SDS and PPOMA form mixed micelles, and SDS and PPOMA aggregation numbers, Nag SDS and Nag PPOMA, have been determined. Total aggregation numbers of the micelles (Nag SDS + Nag PPOMA) and those of SDS decrease upon increasing the weight ratio R = PPOMA/SDS. Localization of PPOMA inside the mixed micelles is considered (i) using 1H NMR to localize the methacrylate function at the hydrophobic core - water interface and (ii) by studying the SDS - PPO micellar system (whose Mw = 400 g·mol-1). Both methods have indicated that the PPO chain of the macromonomer is localized at the SDS micelle surface. Models based on the theorical prediction of the critical micellar concentration of mixed micelles and structural model of swollen micelles are used to confirm the particular structure proposed for the SDS - PPOMA system, i.e., the micelle hydrophobic core is primarily composed of the C12 chains of the sodium dodecyl sulfate, the hydrophobic core - water interface is made up of the SDS polar heads as well as methacrylate functions of the PPOMA, the PPO chains of the macromonomer are adsorbed preferentially on the surface, i.e., on the polar heads of the SDS.