降温速率对偏氟乙烯-三氟乙烯共聚物相转变的影响

Effect of Cooling Rate on the Phase Transition of P(VDF-TrFE) Copolymer

系统研究了降温速率对偏氟乙烯-三氟乙烯共聚物（P（VDF-TrFE））相转变行为的影响。结果表明。P（VDF．TrFE）的DSC降温曲线上存在结晶峰及居里相转变峰。居里相转变过程为一阶相变，包含两个过程：（1）高温居里相转变。具有较少旁氏构象缺陷结构的极性低温相（LT）向非极性高温相（HT）转变；（2）低温居里相转变，长程全反式构象被无规旁氏构象打乱的冷却相（CL）向HT转变。随着降温速率的提高，HT-to-CL和HT-to-LT的转变温度降低，但转变焓值及HT-to-CL与HT-to—LT转变焓的比值均增大，说明降温速率越快越有利于极性相，尤其是CL相的形成。在随后的升温过程中，CL-to-HT的转变温度随着降温速率的提高而升高，而LT-to-HT的相转变温度几乎不变，说明在降温过程中形成CL相的规整度随降温速率的提高而增大。而HT相的熔融温度及熔融焓随降温速率的提高而减小，说明样品在降温过程中没有足够的时问完成结晶，且结晶尺寸减小。由此可以得出，快速降温不利于非极性相HT的形成，但有利于极性相（CL、LT）。尤其是CL相的形成。

A systematic study was carried out on the effect of cooling rate on the phase transitions presented by P（VDF-TrFE） copolymer cooling from melt. The results obtained from differential scanning calorimetry （DSC） show that two-phase transition are observed and the temperatures at which these transition occur are reduced with increasing cooling rate. The concerned curie transition is deciphered as one-step process which is involved two process. The low-temperature crystalline form （LT） presenting a transition at high temperature consists of organized trans sequences with few gauche defects. The cooled crystalline form （CL） consists of the long trans segments with irregular trans-gauche conformation presenting a transition at lower temperature. The transition enthalpy of HT-to-CL and HT-to-LT increase with cooling rate, and the occurrence of HT-to-CL is more favored during fast cooling rate. Upon subsequent heating process, the curie transition temperature of CLoto-HT increases with cooling rate and LT-to-HT is almost unchanged, which is in according with cooling process. The melt temperature and crystallinity of HT form decrease with increasing cooling rate, indicating the sample does not have enough time for crystallization. It can be concluded that rapid cooling is not conducive to the formation of non- polar phase HT, but conducive to the formation of polar phase （CL, LT）, especially CL phase.