Water diffusion in polymer-like reverse micelles. 2. Composition dependence

A pulsed field gradient (FTH)-H-1 NMR study on the system soybean lecithin/ water/perdeuterated cyclohexane, covering a wide range of compositions, is presented. The water diffusion was found to be Gaussian with a well-defined , time-independent, single diffusion coefficient. After the contribution fr om the diffusion of water dissolved in the cyclohexane has been properly ta ken into account, all the data follow the same master curve as a function o f the water to lecithin molar ratio (W-0) The dominating mechanism for the water diffusion was found to be the motion inside giant wormlike reverse ag gregates mediated by an interaggregates exchange with a characteristic time on the order of microseconds. For all the lecithin concentrations investig ated, increasing the value of W-0 increases the water diffusion up to W-0 = 15, where a structural transition toward spherical aggregates causes a dec rease in the water diffusion.