Evidence for spontaneous formation of three-dimensionally periodic cellular structures in a water/oil/surfactant/alcohol system

Upon increasing the temperature, a lyotropic mixture consisting of sodium d odecyl sulfate (SDS), butanol, toluene, and brine solution, with oil and wa ter in equal volumes (midrange mixture), has been shown to order spontaneou sly into two kinds of cubic crystalline arrays exhibiting Fd3m and Pm3n sym metries. Cubic structures, as determined from Rietveld refinements of X-ray powder diffraction profiles, freeze-fracture transmission electron microsc opy observations, and NMR self-diffusion measurements, are consistent with structures in which an aqueous film compartmentalizes the oil nanophase int o polyhedral cells. These cellular networks can be described by space-filli ng combinations of pentagonal dodecahedra with tetrakaidecahedra in one cas e (Pm3n network) and with hexakaidecahedra in the other case (Fd3m network) . There is a close analogy between both oil-in-water cellular structures an d tetrahedrally close-packed (tcp) networks previously proposed as model fo am packings. This midrange system provides a striking example of cellular f luid organizing spontaneously into three-dimensionally ordered polyhedral-f oam-like structures.