Understanding of Face-On Crystallites Transitioning to Edge-On Crystallites in Thiophene-Based Conjugated Polymers
Understanding of Face-On Crystallites Transitioning to Edge-On Crystallites in Thiophene-Based Conjugated Polymers
复制标题
DOI：
10.1021/acs.chemmater.1c00946
复制
发表时间：
2021-06-07
影响因子：
8.6
通讯作者：
You, Wei
中科院分区：
文献类型：
--
作者：
Son, Sung Yun;Park, Taiho;You, Wei
半结晶共轭聚合物薄膜中微晶的取向（相对于衬底平面的面上或边上）对这种薄膜的电荷传输性质具有显著影响。已经在许多共辄聚合物中观察到，其中在铸态膜中主要的正面取向可以在从熔体冷却（熔体退火）时转变为侧面取向。然而，在熔融退火过程中，为什么以及如何从正面微晶转变为侧面微晶仍然不清楚。为了回答这些基本问题，我们设计并合成了一种无规共聚物（RP-3 T），通过插入未取代的三噻吩到区域规则的聚（3-己基噻吩）。RP-3 T在铸态膜中显示出主要的正面取向，但在190 ° C（低于T-m（194 ° C）的温度）下退火时转变为几乎完全的边缘取向。通过对RP-3 T中微晶的微观结构和取向随退火温度的变化进行详细研究，我们发现RP-3 T中的正面微晶在170 ℃（明显低于Tm）时开始消失，而边侧微晶随着退火温度向Tm升高而继续生长。这一发现提供了一个合理的解释，在RP-3 T的热退火过程中，特别是在低于Tm的温度下的面上取向的边缘上的取向的转变。
The orientation of crystallites (face-on or edge-on, in regard to the plane of the substrate) in semicrystalline conjugated polymer thin films has a significant impact on charge transport properties of such thin films. It has been observed in a number of conjugated polymers where predominantly face-on orientation in the as-cast film can transition to edge-on upon cooling from the melt (melt-annealing). However, why and how do face-on crystallites transition to edge-on during melt-annealing remain unclear. To answer these fundamental questions, we designed and synthesized a random copolymer (RP-3T) by inserting unsubstituted terthiophenes into regioregular poly(3-hexylthiophene)s. RP-3T shows a predominantly face-on orientation in an as-cast film but transitioning to an almost exclusively edge-on orientation upon annealing at 190 degrees C, a temperature below the T-m (194 degrees C). Through a detailed investigation on changes in the microstructure and orientation of crystallites in RP-3T with annealing temperature, we find that face-on crystallites in RP-3T start to disappear at 170 degrees C (notably lower than the T-m), while edge-on crystallites continue to grow as the annealing temperature increases toward the T-m. This finding provides a reasonable explanation for the transition of face-on orientation to edge-on orientation during thermal annealing in RP-3T, in particular, at a temperature below the T-m.