Role of Ultrasound on the Control of Liquid–Liquid Phase Separation and Nucleation of <scp>l</scp>-Menthol Polymorphs

This study investigates the influence of ultrasound on the control of liquid–liquid phase separation (LLPS) and the nucleation of l-menthol polymorphs in aqueous solution by varying sonication parameters, including power (750 W at 10, 20, and 30%), pulse rate (10 to 30%), and insonation time (1 to 3 min), under ambient conditions. The results demonstrate that sonication parameters significantly regulate LLPS and induce the polymorphic nucleation of l-menthol. Lower sonication levels resulted in extended nucleation times, promoting the formation of form-II polymorph, while higher sonication levels reduced nucleation times and favored the formation of form-I polymorph in pure aqueous solution. Morphological analysis of nucleated l-menthol polymorphs was performed by optical microscopy, while their internal structure and thermal stability were characterized via powder X-ray diffraction (PXRD) and differential scanning calorimetry (DSC). These findings confirm that ultrasound plays a crucial role in controlling LLPS and in directing the nucleation pathway of l-menthol polymorphs in aqueous solutions.