Effects of entrapped gas on the surface of a plastic ball induced by ultrasonic irradiation on the enhancement of crystallization of acetaminophen form II

Abstract We performed crystallization of the acetaminophen form II by ultrasonic irradiation with a polyethylene (PE) ball or a teflon (PTFE) ball using acetonitrile as a solvent. A PTFE ball enhanced the nucleation probability of form II by ultrasonic irradiation, though the same effect was not observed with a PE ball. The enhancement effect by a PTFE ball was reduced if supersaturated solution with a PTFE ball was evacuated and gas was removed prior to the crystallization. Gas entrapped on the surface of a PTFE ball effectively increased the generation of cavitation bubbles under ultrasonic irradiation, and the cavitation bubbles induced the nucleation of the form II. Therefore, the amount of gases entrapped on the surface of a plastic ball is concluded to be a key parameter for effective crystallization using ultrasonic irradiation. Wettability of a solvent on solid surface dictates the amount of entrapped gases. This study indicated that efficient polymorphic crystallization can be realized by ultrasonic irradiation technique with the help of a plastic ball which features low wettability with solvent.