Role of Molecular Weight in Microstructural Transition and Its Correlation to the Mechanical and Electrical Properties of P(NDI2OD-T2) Thin Films
Role of Molecular Weight in Microstructural Transition and Its Correlation to the Mechanical and Electrical Properties of P(NDI2OD-T2) Thin Films
复制标题
DOI：
10.1021/acs.macromol.1c01481
复制
发表时间：
2021-10
期刊：
影响因子：
5.5
通讯作者：
Kefeng Zhao;T. Zhang;Lu Zhang;Junhang Li;Hongxiang Li;Fangfang Wu;Yu Chen;Qiang Zhang;Yanchun Han
中科院分区：
文献类型：
--
作者：
Kefeng Zhao;T. Zhang;Lu Zhang;Junhang Li;Hongxiang Li;Fangfang Wu;Yu Chen;Qiang Zhang;Yanchun Han
具有高迁移率和机械坚固性的半导体聚合物强烈依赖于它们的分子量。然而，分子质量与溶液链缠结、薄膜微观结构、载流子迁移率和给受体共轭聚合物机械性能之间的关系仍然知之甚少。本文以分子量为34.0 ~ 280 kDa的P（NDI2OD-T2）为模型体系进行了研究。聚合物链在氯仿溶液中表现出三个区域：较少的缠结（34.0 ~ 77.7 kDa），增强的缠结（170 kDa）和严重的缠结（280 kDa）。这种链溶行为导致了三种不同的薄膜微观结构：(1)34.0-77.7 kDa，具有高度有序的链排列和大的晶体长度（lc），但相对较低的系链密度随着mw的增加而增加；(2) 170 kDa，纤维形态小，链排列不太有序，长度仅减小5.6 nm，但结链密度高；(3) 280 kDa，看似无定形的薄膜，在纠缠网络中嵌入大量连接良好的局部聚集体。薄膜结构的变化显著影响了薄膜的电学和力学性能。电子迁移率随分子量的增加而增加，并与系链密度有良好的相关性。相比之下，在34.0 ~ 77.7 kDa时，裂纹起裂应变小于3%，在170和280 kDa时，裂纹起裂应变跃升至36.4±0.9和60.4±2.1%，这与溶液缠结密度密切相关，并可遗传到薄膜中。这项研究有助于刚性链的结构发展，表明含有大量良好连接的局部聚集体和足够的缠结的微观结构有望成为机械坚固的半导体薄膜。
Semiconducting polymers with high mobility and mechanical robust properties are strongly dependent on their molecular weight. However, the relationship between molecular weights and solution chain entanglements, film microstructures, charge carrier mobility, and mechanical properties for donor–acceptor conjugated polymers remains less understood. Herein, P(NDI2OD-T2) with a weight-average molecular weight (Mw) from 34.0 to 280 kDa was investigated as a model system. The polymer chain exhibited three regions in chloroform solutions: fewer entanglements (34.0–77.7 kDa), enhanced entanglements (170 kDa), and severe entanglements (280 kDa). This chain solution behavior resulted in three distinct film microstructures: (1) 34.0–77.7 kDa, liquid-crystalline-like morphologies with highly ordered chain arrangements and large crystallite lengths (lc) yet relatively low tie-chain densities that increased withMw; (2) 170 kDa, small fibril morphology with less ordered chain arrangements and a decreasedlcof only 5.6 nm yet a high tie-chain density; and (3) 280 kDa, a seemingly amorphous film with vast well-connected local aggregates embedded in an entangled network. The structural change in films significantly affected the electrical and mechanical performances. The electron mobility increased continuously withMw, correlating well with the tie-chain density. By contrast, the crack-onset strain was less than 3% at 34.0–77.7 kDa and then jumped to 36.4 ± 0.9 and 60.4 ± 2.1% for 170 and 280 kDa, showing a close correlation with the solution entanglement density, which could be inherited into films. This study contributes to structural development of rigid chains withMwand demonstrates that the microstructure containing vast well-connected local aggregates and adequate entanglements is promising toward mechanically robust semiconducting films.