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

本研究旨在探索寻找比目前所评价的氟化膜耐热性更高的聚合物压电膜的可能性。研究思路的起源是发现聚对苯对苯二甲酰胺（PPTA）的分子在PPTA晶体中以90个º的角度在230ºC左右旋转，尽管它的耐热性高达510ºC。利用这一运动，在高温、高电场条件下进行极化，可以实现高耐热膜的制备。1990年，采用PPTA薄膜，在230ºC左右的晶体弛豫温度下进行了极化。然而，发现压电常数低至0.05pC/N。其原因是由于PPTA的晶体结构异常稳定，结晶度高，带来的效果非常少。可用于压电的酰胺基团。因此，在1991年，聚（间苯苯二苯酰胺）（PRIA）被用于压电薄膜，其结晶度低于PPTA。经过多次试验，出乎意料地发现PNIA薄膜在低于非晶区玻璃化转变温度100℃时的极化使得压电常数为0.4pC/N，而最高可保持在300℃。结构检测表明，60%的压电分配到非晶区，40%分配到结晶区。利用PNIA的单轴单平面定向膜，有望进一步提高其性能。

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.