Fig. 4

POM observations and FSC measurements of the PI films. The POM images were acquired under a nitrogen atmosphere. A Untreated samples at 30 °C, B treated samples at 30 °C, 350 °C, and samples after cooling to 30 °C. C FSC results for a heating rate of 10,000 °C/s, showing the temperatures that correspond to the main endothermic and exothermic peaks