MESOMORPHIC PHASES .I. X-RAY STUDIES OF DIMETHYLDODECYLAMINE OXIDE-DEUTERIUM OXIDE SYSTEM

A detailed X-ray study has been made of the lyotropic mesomorphic phases found in the dimethyldodecylamine oxide-deuterium oxide system. Discontinuities are found in the X-ray long spacings at phase boundaries approached by changing either the concentration of surfactant or the temperature. The positions of the phase boundaries agree well with previously published phase diagrams of this system. The data indicate two-phase regions near the boundaries, proving that the phase transitions are first order. The data have been examined to test the various structures proposed for the mesophases. Although the data can be explained using a cylindrical model for the middle phase, the face-centered-cubic structure for the viscous isotropic phase, and a lamellar structure for the neat phase as has been proposed for other mesomorphic systems, in this system it appears, in addition, that the structural units are composed of surfactant and associated water.