As can be seen from Fig. 4c and d, longer irradiation durations of 10 and 15 s were also studied. Nevertheless, there was no remarkable difference on the nucleation temperature between those two durations. Nucleation temperatures (-2.3 and -2.4 C) for those two durations (10 and 15 s) were lower than the 7 s treatment (-1.6 C), while they were almost as high as the control samples (-2.6 C). This suggested that too long ultrasound durations could not significantly affect the nucleation temperature.