Aggregate size and surfactant/hydrocarbon diffusion in the cubic phase of the sodium octanoate/hydrocarbon/water system

The cubic liquid crystalline (I-1) phase formed by sodium octanoate, n-octane, and water (40.0:4.0:56.0% by weight) was studied by means of a fluorescence quenching (FQ) technique. Time resolved fluorescence was measured for small amounts of solubilized pyrene (P), both with and without a solubilized quencher (Q), dimethylbensophenone. The FQ data show that the Q and P molecules are captured in closed amphiphilic aggregates consisting of ca. 75 sodium octanoate molecules at 298 K. From these results together with already published X-ray data the number of micelles per unit cell was estimated to be eight. NMR self-diffusion studies of the surfactant and the hydrocarbon were carried out on the above mentioned cubic phase as well as on the corresponding phases formed with p-xylene and cyclohexane. These experiments convey information on the lifetime of the surfactant and the hydrocarbon in the aggregates and also on the structure of the cubic phase. (C) 1996 Academic Press, Inc.