Simultaneous synchrotron radiation X-ray diffraction-DSC analysis of melting and crystallization behavior of trilauroylglycerol in nanoparticles of oil-in-water emulsion

Crystallization, polymorphic transformation, and melting behavior of nanoparticles of trilauroylglycerol (LLL) in oil-in-water (O/W) emulsion were examined initially by DSC, and then by simultaneous synchrotron radiation small-angle (SAXS) and wide-angle (WAXS) X-ray diffraction and DSC (SR-SAXS /WAXS/DSC). The O/W nanoparticles emulsions having average diameters of 42 to 120 nm were prepared by application of mechanical shear using a high-pressure homogenizer. The following results were obtained: (i) The DSC study showed that the melting temperature of the stable β form of LLL was reduced from 46.7 (bulk) to 26.5–44.0°C (nanoparticles); this variation as assumed to be due to the size distribution of the nanoparticles. Crystallization temperature was also reduced from 18.9 (bulk) to −9.5±0.5°C (nanoparticles). These results were consistent with those of previous studies of nanoparticles of fats obtained in the O/W emulsion. (ii) The results obtained by the SR-SAXS/WAXS/DSC technique during the cooling process to −20°C showed that the first-occurring polymorph of LLL in the bulk liquid was β′, whereas α was first nucleated and transformed to β′ around −10°C during cooling in the nanoparticles. (iii) The SR-SAXS/WAXS/DSC data taken during the heating process from −20°C after the crystallization showed that β′ transformed to β around 0°C and that the melting of β started at 30°C and ended at 44°C. The present study showed that forming nanoparticles of LLL in the O/W emulsion having the diameters of 42 to 120 nm reduced the melting and crystallization temperatures and increased the transformation rate of α→β′→β in comparison to the LLL crystals formed in the bulk phase.