Micellar growth in hexagonal phases of lipid systems

Measurements are reported of the unit cell parameter a of the oleoyl-lyso-phosphatidyl-choline--water system in the hexagonal phase H as a function of the paraffinic volume concentration cv,par. A functional behavior a{∝}cv,par^-x, with x1/3, has been derived. It is shown that this behavior characterizes micellar growth along the hexagonal domain, with nearly spherical micelles at the isotropic I-H phase transition and practically infinite cylindrical micelles at the H-Q²³⁰ (cubic bicontinuous, space group Ia3d) phase transition. These results are compared with other systems for which x=1/3 or 1/2 and with recent statistical-mechanical calculations for systems with self-association.