Abstract:

Ordered bicontinuous microstructures formed in a fully water-dilutable, pseudoternary unique nonionic microemulsion were obtained and characterized. The conc. contained a mixt. of triacetin/D-$\alpha$-tocopherol acetate/ethanol/Tween 60. Upon diln., the conc. was transformed from a reversed micellar system to oil-in-water microemulsion droplets. The transformation occurred through an intermediate phase of ordered bicontinuous structures. The factors that governed the construction of this unique phase, and its phys. and structural properties, were characterized in detail. The techniques used included small angle X-ray scattering (SAXS), self-diffusion and quantum filtered NMR, differential scanning calorimetry, rheol. measurements, elec. cond., and dynamic light scattering. This mesophase displays microemulsion properties along with some characteristics of lyotropic liq. crystals (but is not a mixt. of the two). Similar to microemulsions, the structures were transparent and spontaneously formed and exhibited thermodn. stability. Yet, unlike microemulsions, they showed short-range order at room temp. Addnl., the microstructures exhibited non-Newtonian flow behavior, characteristic of lamellar structures. The bicontinuous ordered microemulsions were obtained upon heating (to 25 °C) from the lamellar phase existing at low temps. (5 °C). The main feature governing the bicontinuous mesophase formation was the amphiphilic nature of oil blends composed of D-$\alpha$-tocopherol acetate and triacetin. The oils functioned as cosurfactants, altering the packing parameter of the surfactant and leading to the construction of bicontinuous structures with short-range order. These unique structures might have drug or nutraceutical delivery advantages. [on SciFinder(R)]