Abstract
The crystallization behavior of trilaurin (LLL) without and with application of ultrasonic power is investigated in-situ using synchrotron radiation time resolved small angle X-ray scattering (SAXS) and wide angle X-ray scattering (WAXS) simultaneous measurement. Without ultrasound application, both polymorhic forms β' and β crystallised in the melt. With ultrasound treatment of the melt, the following effects were observed: (i) a marked decrease of induction times for crystallisation of LLL, (ii) an increased nucleation rate, and (iii) a crystallisation of only β forms for LLL under conditions of initial crystallisation temperature of 30℃, and applied ultrasound of 2s. In addition to this, a crystallisation of LLL under lower initial crystallisation temperature of 25℃ and with the same ultra-sonication time of 2s, revealed the presence of both β' and β polymorphs. This suggests that crystallisation of only β form does not only depend on ultrasound treatment, but on the initial temperature of crystallization, as well. Based on the dynamic nucleation of LLL crystals induced by collapsing caviatation bubbles, we argue that a pronounced decline in induction times and increase of nucleation rate, result from the melting points shift due to high pressure pulses associated with collapsing bubbles. Insufficiency of this approach to account for the nucleation of only β polymorph or both β' and β polymorphs was also considered.
