STRUCTURAL-CHANGES IN THE ISOTROPIC-PHASE OF THE TERNARY SURFACTANT SYSTEM - TETRADECYLDIMETHYLAMINE OXIDE BENZYL ALCOHOL/WATER/

The surfactant system tetradecyldimethylamine oxide (TDMAO)/ benzyl al cohol/water has been studied. In the phase diagram of this ternary sys tem a large isotropic region is encountered that connects the water co rner to the benzyl alcohol corner. This isotropic phase has been inves tigated in some detail by means of electric conductivity, viscosity, e lectric birefringence, and small-angle neutron scattering (SANS) measu rements. From these experiments it can be concluded that for roughly e qual amounts of alcohol and water a bicontinuous structure is present, similar to that typically observed for bicontinuous microemulsions. T he structural units present become continuously smaller with increasin g alcohol content, and at very high alcohol content only small reverse aggregates are present. The formation of this bicontinuous phase can be understood by the fact that the presence of the benzyl alcohol redu ces the stiffness of the surfactant film, and therefore such a ''spong e''-type structure is favored. With increasing surfactant concentratio n the amphiphilic film becomes stiffer again, which leads to the forma tion of a lamellar phase. The corresponding phase boundary is exactly related to the amphiphilicity factor as it can be deduced from the sca ttering experiments. (C) 1998 Academic Press.