Small Angle Neutron Scattering Study of Microstructural Transitions in a Surfactant-Based Gel Mesophase

A surfactant-based rigid gel mesophase containing bis(2-ethylhexyl) sodium sulfosuccinate (AOT), phosphatidylcholine (lecithin), 2,2,4-trimethylpentane (isooctane), and D 2 O has been characterized using small angle neutron scattering (SANS). The addition of water to a solution of AOT and lecithin in isooctane leads to a dramatic increase in viscosity and the formation of a rigid gel as the water content is increased above a specific threshold. SANS profiles indicate that these gels have a crystalline microstructure with characteristic dimensions that are clearly correlated to the system's water content and temperature. The scattering patterns are consistent with models that describe the microstructure as columnar hexagonal at lower water contents and temperatures and lamellar at higher water contents and temperatures. SANS is also able to examine characteristics of the intermediate region where the two phases coexist and to calculate the characteristic dimensions of these microstructures. The rigidity of the gel indicates that the system may be useful in templated materials synthesis.