A long ripple phase in DLPC–decylglucoside mixture evidenced by synchrotron SAXS coupled to DSC

For the first time, the secondary ripple phase in a system containing dilauroyl phosphatidylcholine (DLPC) is observed by small-angle X-ray diffraction (SAXS). The SAXS profile exhibits many well-resolved peaks. The fast formation of this phase upon cooling from the liquid crystalline lamellar phase Lα is induced by addition of C10G with molar ratio 0.17 ≤ R = [C10G]/[DLPC] ≤ 0.49. For R < 0.17, the primary Pβ′ ripple phase is observed. In contrast to the Pβ′ phase, which shows a sawtooth shape, the secondary ripple structure is thought to be symmetric. The ripple length (190 Å) and the bilayer spacing (74 Å) are larger than in the primary ripple phase. Lattice parameters of the new long ripple phase, which are quite insensitive to temperature, vary slightly linearly with R. In this study, structural and thermodynamic changes within the samples were followed as a function of temperature by time-resolved X-ray diffraction coupled to DSC.