Synchrotron Radiation SAXS/WAXS Study of Polymorph-Dependent Phase Behavior of Binary Mixtures of Saturated Monoacid Triacylglycerols

Polymorphic influences on the phase behavior of three types of binary mixtures of saturated monoacid triacylglycerols (TAGs), trilaurin/trimyristin (LLL/MMM), trilaurin/tripalmitin (LLL/PPP), and trilaurin/tristearin (LLL/SSS), were examined by small- and wide-angle X-ray scattering (SAXS/WAXS) using synchrotron radiation. The carbon numbers (C n ) for the fatty acid chains of the three TAGs are 12 (LLL), 14 (MMM), 16 (PPP), and 18 (SSS). In the LLL/MMM system, miscible phase behavior occurred in metastable α and β‘ forms, whereas the most stable β form exhibited a eutectic phase. On the other hand, LLL/PPP and LLL/SSS mixtures showed immiscible phases for α, β‘, and β forms. Therefore, the TAG binary mixtures were miscible in metastable polymorphs of α and β‘ forms when C n differed by 2, whereas the immiscible mixtures were constructed in all polymorphic forms when C n differed by 4 and 6.