Ultrasound assisted nucleation and growth characteristics of glycine polymorphs – A combined experimental and analytical approach

Abstract

For the first time, the effect of ultrasound in the diagnostic frequency range of 1-10 MHz on the nucleation and growth characteristics of glycine has been explored. The investigation employing the ultrasonic interferometer was carried out at a constant insonation time over a wide range of relative supersaturation from σ=-0.09 to 0.76 in the solution. Ultrasound promotes only α nucleation and completely inhibits both the β and γ nucleation in the system. The propagation of ultrasound assisted mass transport facilitates nucleation even at very low supersaturation levels in the solution. The presence of ultrasound exhibits a profound effect on nucleation and growth characteristics in terms of decrease in induction period, increase in nucleation rate and decrease in crystal size than its absence in the solution. With an increase in the frequency of ultrasound, a further decrease in induction period, increase in nucleation rate and decrease in the size of the crystal is noticed even at the same relative supersaturation levels. The increase in the nucleation rate explains the combined dominating effects of both the ultrasound frequency and the supersaturation in the solution. Analytically, the nucleation parameters of the nucleated polymorph have been deduced at different ultrasonic frequencies based on the classical nucleation theory and correlations with the experimental results have been obtained. Structural affirmation of the nucleated polymorph has been ascertained by powder X-ray diffraction.

Sonocrystallisation: Observations, theories and guidelines

“…Ultrasound has also the potential to produce crystals with a different polymorphic form compared to silent conditions [99][100][101][102][103][104][105]. This change in polymorphic form is, however, not observed in all papers in literature which investigated the effect of ultrasound on polymorphism [91,106,107]. The stability of the formed polymorph and the conditions under which ultrasound is applied seem to define whether a change in polymorph is observed or not [77,105,108].…”

Establishment of a Continuous Sonocrystallization Process for Lactose in an Oscillatory Baffled Crystallizer

“…This cavitation generates high local supersaturation leading to spontaneous nucleation in otherwise unsaturated liquid. The acoustic streaming, microstreaming, and highly localized temperature and pressure within the fluid causes spontaneous induction of primary nucleation, reduction of crystal size, inhibition of agglomeration, and manipulation of crystal size distribution. − Sonication can promote fines in batch processes, so sonication should only be used for nucleation, and then production of larger crystals can be achieved by growth of those seed crystals.…”

The Improvement Effect and Mechanism of Longitudinal Ultrasonic Vibration on the Injection Molding Quality of a Polymeric Micro-Needle Array

“…During LUμIM process, the micromorphology in the crystalline region of the semi-crystalline polymer was recognized to be affected by ultrasonic vibration in many aspects. First, the high frequency reciprocating motion of polymer chains and the cavitation effect in the melt under the action of ultrasonic vibration led to high pressure, an intense heating effect, and a rapid heat transfer rate in local region of the micro cavity, especially near the upper surface of ultrasonic horn, and formed a uniform and compact arrangement of polymer chains, subsequently promoting the crystallization nucleation process and increasing the nucleation rate [23]. Second, the polymer chain tends to disorder under the effect of ultrasonic vibration, the common shish-kebab structure in traditional micro-injection molded part turned into a two-dimensional or three-dimensional crystal structure so that the space dimension of crystal growth was increased [24].…”