Kinetics and Mechanism of the Lamellar to Gyroid Inverse Bicontinuous Cubic Phase Transition

In this paper, we present data on the transition from the lamellar (L α ) to the gyroid inverse bicontinuous cubic ( ) mesophase. The system investigated was 2:1 lauric acid (LA)/dilauroylphosphatidylcholine (DLPC), at a fixed overall hydration of 50% water by weight. The phase transition was induced by a pressure jump and monitored by time-resolved X-ray diffraction (TRXRD). We observe the gradual appearance of signals from the emergent phase and an accompanying disappearance of signals from the initial L α phase. These changes correspond to a transformation occurring over a time scale which varies between seconds and minutes. We further observe that the lattice parameters of both the initial L α and final phases change throughout the transformation. We suggest that this reflects a competition between the two phases for the limited amount of water available. In addition, we suggest a mechanism whereby the transformation from L α to proceeds via an intermediate phase, which we suggest is the diamond inverse bicontinuous cubic phase ( ). We present evidence for its identity and suggest mechanistic pathways for its formation from the L α phase and subsequent transformation into the phase.