FIGURE 4 Pseudocolor thermal images of the front view of the MMT-PI subjected to the alcohol lamp flame at different times (0 s~90 s). Time dependence of the center of the cotton ball temperature (last one).
The cotton ball was selected as the observation object, where C1 is the periphery and P1 is the center of the cotton ball, respectively. The maximum temperature of C1 was detected to be close to 70 oC when the alcohol lamp was once lit. This may be due to the small thickness of MMT-PI and the short longitudinal distance of heat transfer, which makes it easier to reach the high temperature of the MMT-PI mentioned above. Later, the temperature gradually decreased, probably due to the increased heat conduction along the plane direction. Therefore, the temperature of C1 dropped to about 45oC, subsequently kept at a constant value of no more than 50 °C. During the recorded 90 s, the cotton ball was not ignited. On the contrary, both C1 and P1 reached the maximum temperature after contact with the flame for 33 s for DABPPI (Fig. S4 in Supporting Information), and the cotton ball ignited immediately upon exposure to the flame and burned off in 9 s.