Melting characteristic
The evolution of the melting characteristic with time of MKF crystallized at 25 °C without and with HIU application is given in Fig. 3. For the crystallization without HIU, the sample did not exhibit any peak at t = 5 min (Fig. 3a). At 15-30 min, the sample started to melt at 27.6-27.7 °C and showed a relatively broad melting peak at 28-29 °C (Table 2). At 45 and 60 min, the sample began to melt at higher temperature (∼31 °C) and the melting peak became much broader, the location of which moved to a significantly higher peak temperature of ∼35 °C (p < 0.05) with a decrease in the melting enthalpy (ΔH) (p < 0.05). This suggests that there was a phase transition of MKF from a less stable form to a more stable one after 30 min of crystallization. With HIU (70% amplitude), MKF had already started to crystallize at 5 min with one melting peak at ∼28 °C (Fig. 3b and Table 2), indicating that, at the early stages, MKF in the experiments without and with HIU solidified into the same polymorphic structure (p > 0.05). At 15 min, the melting peak location moved to ∼33 °C with a decrease in ΔH, indicating the polymorphic transformation of MKF at this crystallization time and suggesting that the phase transition of MKF that crystallized with the application of HIU occurred sooner than MKF that crystallized without HIU. At 45 and 60 min, the melting peak moved to higher temperature (∼35 °C) with an increase in ΔH from that of 15 min.