A STUDY OF THE MICROSTRUCTURE OF A 4-COMPONENT NONIONIC MICROEMULSIONBY CRYO-TEM, NMR, SAXS, AND SANS

One recently reported application of microemulsions is as a fire-resis tant hydraulic fluid where efficacy and stability depend among other f actors upon the water-solubilizing capacity of the microemulsion and o n the relative concentration of the surfactant. A model for such a mic roemulsion system has been studied using cryo-transmission electron mi croscopy (cryo-TEM), H-1 NMR self-diffusion, and small angle X-ray (SA XS) and neutron scattering (SANS). The phase behavior of the system co ntaining a 1:1:2 oil:alcohol: surfactant weight ratio is characterized by a single continuous microemulsion region starting from a solution containing no water and approaching the water corner. Along this dilut ion line, a structural transition sequence: oil drops --> short range, noncontinuous lamellar microstructure --> weakly hydrated aggregates is inferred as the water concentration is decreased. The local lamella r microstructure, i.e., stacks of surfactant sheets, oil, and water, r andomly oriented in space without the long range correlations that cha racterize a lamellar liquid crystal is imaged for the first time.