Stability of inverse bicontinuous cubic phases in lipid-water mixtures

We investigate the stability of seven inverse bicontinuous cubic phases [G, D, P, C(P), S, I-WP, F-RD] in lipid-water mixtures based on a curvature mo del of membranes. Lipid monolayers are described by parallel surfaces to tr iply periodic minimal surfaces. The phase behavior is determined by the dis tribution of the Gaussian curvature on the minimal surface and the porosity of each structure. Only G, D, and P are found to be stable, and to coexist along a triple line. The calculated phase diagram agrees very well with ex perimental results for 2:1 lauric acid/DLPC.