Synthesis of LL-leucine nanoparticles via physical vapor deposition at varying saturation conditions

Preparation of LL-leucine nanoparticles by a process based on physical vapor deposition has been presented. In an aerosol flow reactor method, aqueous LL-leucine droplets were first dried followed by the sublimation of LL-leucine to produce vapor that upon vapor deposition resulted in LL-leucine nanoparticles with size ranging from 40 to 200 nm. Onset temperature for the sublimation of LL-leucine at concentrations from 0.02 to 1.34g/m3 increased from 135 to 175∘C, respectively. The formation of nanoparticles was initiated in three different ways: (i) via droplet drying, (ii) via heterogeneous nucleation of LL-leucine vapor on solid LL-leucine particles, and (iii) via homogeneous nucleation of LL-leucine vapor to form new-born nanoparticles. Consequently, the saturation conditions of LL-leucine vapor in the reactor determined the resulting particle size, size distribution and number concentration, those depending very much on nucleation mode. In general, the both nucleation modes produced narrow size distributions, that is, geometric standard deviation (GSD) was <1.8<1.8 although the number concentration increased with the increased amount of LL-leucine vapor. Upon desublimation and vapor deposition, LL-leucine formed leafy crystals whose size was the largest when produced from the heated section at the vicinity of the onset temperature and the smallest far above the onset temperature. All the particles prepared in the conditions (i)–(iii) were crystalline. However, X-ray diffraction analysis showed preferential direction for crystal growth according to the way of particle formation.