Abstract:

The Winsor IV microemulsion system composed of octaethylene glycol monododecyl ether [C12(EO)8]/dodecane + pentanol (1:1 by wt.)/water has been investigated at const. temp. using small-angle x-ray scattering and elec. cond. measurements. The results are interpreted in terms of structural evolution of the mol. aggregates as a function of the stepwise addn. of water or (oil + alc.). The size and shape of a variety of microstructures are described: small, spherical micelles near the water corner, and hexagonal and lamellar mesophases, which are oil- and alc.-poor. Simple multishell models provide some insight into how diln. with water or swelling with (oil + alc.) influences the overall symmetry of the aggregates, pentanol and dodecane partitioning, surfactant headgroup conformation, and the contribution of pentanol to oil solubilization. The previously identified "local" lamellar structure, which is a surfactant-rich and (oil + alc.)-rich intermediate state between the W/O and O/W regions, is characterized here as a type of ordered, but highly obstructed, bicontinuous microemulsion. [on SciFinder(R)]