Control the interplay of crystallization and phase separation of conjugated polymer blends by the relative rate of nucleation and growth

Abstract

In terms of the solution processing conjugated polymer blends, having a comprehensive understanding of the relationship between crystallization and phase separation is significant to optimize their performance. However, crystal nucleation and crystal growth are usually coupled during the process of the film formation process, and it is sometimes difficult to distinguish their respective effects on phase separation. We propose that apply the temperature-dependent aggregation (TDA) features of poly[(5,6-difluoro-2,1,3-benzothiadiazol-4,7-diyl)-alt-(3,3‴-di(2-octyldodecyl) 2,2′; 5′,2″; 5″,2‴-quaterthiophen-5,5‴-diyl)] (PffBT4T-2OD) to separate both nucleation and growth processes and conduct the investigation of their effects on phase separation of PffBT4T-2OD/N2200 (poly[[N,N′-bis(2-octyldodecyl)-napthalene-1,4,5,8-bis(dicarboximide)-2,6-diyl]-alt-5,5′-(2,2′-bithiophene)]) blends. It can be discovered that the nucleation and growth of the blends system can be distinguished to three regions: Region I: dominated by the nucleation process (T is 25 °C–65 °C); Region II: dominated by both nucleation and growth processes (T is 65 °C–100 °C); and Region Ⅲ: dominated by the growth process (T is 100 °C–120 °C). In situ absorption spectroscopy and Urbach (Eu) are adopted to investigate the crystallization rate and crystal perfection in three regions. The different relative rates of nucleation and growth exert an impact on the interplay between crystallization and phase separation, which results in completely different morphology.