Studies on piezoelectricity and pyroelectricity of Aramid film by mean of poling at high temperature and high voltage

本研究的目的是探索寻找一种耐热性优于目前所评价的氟膜的高分子压电膜的可能性。研究思路的起源是发现聚对苯撑二甲酰胺（PPTA）分子在PPTA晶体中的旋转角在230 ℃左右，尽管PPTA具有510 ℃的高耐热性。1990年，PPTA膜被采用，并在230 ℃左右的温度下进行了极化，该温度对应于结晶弛豫温度。然而，发现压电常数低至0.05pC/N。究其原因，是PPTA的晶体结构异常稳定，结晶度很高，使PPTA的结晶度很低。酰胺基团可用于压电性。因此，在1991年，聚（间亚苯基乙酰胺）（PRIA）被用于压电膜，其具有比PPTA低的结晶度。经过多次实验，出乎意料地发现，在低于非晶区玻璃化转变温度的100 ℃下极化PNIA膜，得到的压电常数为0.4pC/N，保持高达300 ℃。结构检查显示，60%的压电性分配给非晶区和40%的结晶区。通过使用PNIA的单轴单平面取向膜，预期进一步改进。

This research was proposed to explore the possibility of finding the polymeric piezoelectric membrane with higher heat-resistance than the fluorinic membranes evaluated until now. The origin of the research idea was in finding the fact that the molecules of poly (p-phenyleneterephthalamide) (PPTA) rotate in the crystal of PPTA around 230ﾟC by the angle of 90ﾟ in spite of its high heat-resistance of 510ﾟC. By utilizing this motion, if the poling at high temperature and high electric field is carried out, the membrane with high heat-resistance will be realized.In 1990, the membrane of PPTA was taken up and the poling was carried out at the temperatures around 230ﾟC which corresponds to the crystalline relaxation temperature. The piezoelectric constant was found however to be as low as 0.05pC/N. The reason for it was ascribed to the unusually stable crystal structure of PPTA and high degree of crystallinity, which brought very few. amide groups available for piezoelectricity. Thus, in 1991, poly (m-phenyleneisophthalamide) (PRIA) was used for the piezoelectric film, which has lower crystallinity than PPTA. After many trials, it was found unexpectedly that the poling of PNIA film at 100ﾟC lower than the glass transition temperature of the amorohous region gave the piezoelectric constant was 0.4pC/N which was held as high as 300ﾟC. Structural inspection revealed that the 60% of piezoelectricity is assigned to the amorphous region and 40% to the crystalline region. Further improvement is expected by using uniaxially uniplanar oriented film of PNIA.