Synchrotron radiation X-ray diffraction study on phase behavior of PPP-POP binary mixtures

The phase behavior of the sn-1,3-dipalmitoyl-2-oleoylglycerol (PPP-POP) binary mixture system was studied by powder X-ray diffraction with synchrotron radiation and by differential scanning calorimetry. The results showed that the immiscible phases were observed in metastable and in the most stable forms. In particular, synchrotron X-ray diffraction enabled us to reveal the monotectic nature of alpha as a kinetic phase be -havior. The equilibrium phase diagram of the PPP-POP mixture is divided into two regions. In POP concentration ratios below 40%, solid-state transformation from alpha to beta was observed, indicating that the alpha-beta transition of PPP was promoted in the presence of POP. By contrast, the polymorphic transition proceeds from alpha to beta through the occurrence of the intermediate beta' form at POP concentration ratios above 50%.