The lyotropic ribbon phase and its transformation to the lamellar phase in the potassium N-dodecanoyl-dl-alaninate/water/decanol system

Abstract

We have studied the variation in the aggregate size, shape and the unit cell of the rectangular ribbon (R₁) phase formed between the hexagonal (H₁) and the lamellar phase with water defects (L_α ^H phase) in the potassium N-dodecanoyl-dl-alaninate/water/1-decanol system. With an increase in surfactant concentration at roughly constant decanol concentration, the aspect ratio, ρ, of the aggregate increases, whereas the rectangular unit cell shrinks, suggesting a decreasing separation between the ribbonlike aggregates. Similarly increasing decanol concentration at fixed surfactant-to-water ratio increases the unit cell width and ρ. The small-angle X-ray scattering results establish an epitaxial relationship between the (11) plane of the R₁ phase and the (10) plane of the L_α ^H phase. This suggests that with successive addition of decanol, the ribbons of the (11) plane of the R₁ phase come closer and partially merge along their length, forming a surfactant bilayer pierced with water defects (L_α ^H phase).

Acknowledgement: We are thankful to A. M. Lopez-Quintela, Department of Physical Chemistry, University of Santiago Compostela, Santiago de Compostela, Spain, for his valuable comments and suggestions.