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

A pulsed field gradient FT1HNMR 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 from the diffusion of water dissolved in the cyclohexane has been properly taken into account, all the data follow the same master curve as a function of the water to lecithin molar ratio (W0). The dominating mechanism for the water diffusion was found to be the motion inside giant wormlike reverse aggregates mediated by an interaggregates exchange with a characteristic time on the order of microseconds. For all the lecithin concentrations investigated, increasing the value of W0 increases the water diffusion up to W0 = 15, where a structural transition toward spherical aggregates causes a decrease in the water diffusion. © 1999 American Chemical Society.