Non-equilibrium formation of the cubic Pn3m phase in a monoolein/water system

Time-resolved small-angle X-ray diffraction experiments have been carried out to investigate the transformation from the cubic gyroid $Ia3d$ to the cubic diamond $Pn3m$ phase. The transition was induced by rapid addition of water to a monoolein/water system changing the initial water concentration of 26% w/w to excess of water conditions. The transformation proceeds in two steps: at the beginning, the two cubic mesophases have a strongly differing lipid/water composition and are accompanied by an intermediate phase. This phase vanishes as the ratio of cell parameters exceeds 1.50. Thereafter, the transition continues by a direct nearly isoareal transformation of the cubic minimal surfaces. Lateral area per lipid molecule, molecular shape and principle curvatures are about the same in this regime.