Abstract:

One recently reported application of microemulsions is as a fire-resistant hydraulic fluid where efficacy and stability depend among other factors upon the water-solubilizing capacity of the microemulsion and on the relative concn. of the surfactant. A model for such a microemulsion system has been studied using cryo-transmission electron microscopy (cryo-TEM), 1H NMR self-diffusion, and small angle X-ray (SAXS) and neutron scattering (SANS). The phase behavior of the system contg. a 1p1:2 oil:alc.:surfactant wt. ratio is characterized by a single continuous microemulsion region starting from a soln. contg. no water and approaching the water corner. Along this diln. line, a structural transition sequence: oil drops → short range, noncontinuous lamellar microstructure → weakly hydrated aggregates is inferred as the water concn. is decreased. The local lamellar microstructure, i.e., stacks of surfactant sheets, oil, and water, randomly oriented in space without the long range correlations that characterize a lamellar liq. crystal is imaged for the first time. [on SciFinder(R)]