Effect of particle size on colloidal solid triglycerides

The size-dependent behavior of different crystalline, colloidal monoacid an d complex triglycerides in aqueous dispersion is investigated, mainly by di fferential scanning calorimetry and X-ray diffraction. With decreasing part icle size the melting range of the triglycerides broadens and shifts to low er temperatures. The melting of particles in small-size dispersions (e.g., with mean particle sizes around 100 nm) of even, saturated monoacid triglyc erides such as tripalmitin and trimyristin is characterized by a sequence o f discrete sharp transitions which are not due to polymorphism. This comple x melting process is observed with different types of stabilizers. The sequ ence of melting events originates from the shape and layered structure of t he triglyceride nanocrystals leading to successive discrete transitions cor responding to the melting of particle fractions with different thickness. I n dispersions of complex triglycerides, the individual transitions are less sharp or even undetectable. The heat of fusion and the crystallization tem perature of the nanoparticles decrease slightly with decreasing particle si ze whereas the rate of polymorphic transitions increases. Moreover, dispers ions containing extremely small nanoparticles display an X-ray diffraction pattern indicating the presence of a crystal form that seems not to have be en described previously for these triglycerides.