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

摘要

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 beta form of LLL was reduced from 46.7 (bulk) to 26.5-44.0degreesC (nanoparticles); this variation was assumed to be due to the size distribution of the nanoparticles. Crystallization temperature was also reduced from 18.9 (bulk) to -9.5 +/- 0.5degreesC (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 -20degreesC showed that the first-occurring polymorph of LLL in the bulk liquid was beta', whereas alpha was first nucieate and transformed to beta' around -10degreesC during cooling in the nanoparticles. (iii) The SR-SAXS/WAXS/DSC data taken during the heating process from -20degreesC after the crystallization showed that beta' transformed to beta around 0degreesC and that the melting of beta started at 30degreesC and ended at 44degreesC. 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 alpha --> beta' --> beta in comparison to the LLL crystals formed in the bulk phase.