LOCAL PROPERTIES OF AN AOT MONOLAYER AT THE OIL-WATER INTERFACES - NMR MEASUREMENTS

The penetration of alkanes of different chain lengths in bilayers of AOT in the system AOT/brine/n-alkane is investigated by NMR measurements. For short chains (carbon number N < 11), the phase is lamellar. For longer chains, the phase is bicontinuous or lamellar depending on the salinity. It appears that, for N < 11, the alkane molecules penetrate easily in the AOT monolayers. For N > 11, when the phase is a bicontinuous one, the answer is not so straightforward because the phase is isotropic. For the anisotropic phases which contain small amounts of a long-chain alkane the solubilization of the alkane in the AOT monolayers is very weak. Short alkanes (N < 11) behave like a ''good'' solvent for the paraffinic chains of the AOT molecules and long alkanes (N > 11) like a ''poor'' solvent.