PffBT4T基共轭聚合物温度相关溶液组装的变温散射和光谱表征《ACS Applied Polymer Materials》

PffBT4T基共轭聚合物温度相关溶液组装的变温散射和光谱表征

摘要

从中浇铸薄膜的共轭聚合物（CPs）的溶液结构对于裁剪薄膜形态从而调整器件性能至关重要。在这里，我们使用多模变温散射和光谱学工具对不同组装温度下具有不同侧链长度的聚[(5,6-二氟-2,1,3-苯并噻二唑-4,7-二基)-alt-(3,3‴-二烷基-2,2′; 5′,2''; 5'',2‴-四噻吩-5,5‴-二基)]（PffBT4T）聚合物的溶液组装进行了全面量化。通过紫外-可见光谱（UV-vis）、核磁共振（NMR）、动态光散射（DLS）和小角中子散射（SANS），发现基于PffBT4T的CPs的构象和聚集行为对温度和侧链长度都非常敏感。我们发现，随着侧链长度从2-辛基十二烷基（C8C12）略微增加到2-壬基十三烷基（C9C13），基于PffBT4T的CPs在聚集到溶解链的转变温度（10°C）、聚集度、聚集焓变化和溶液中聚集物的大小方面显著降低。在室温下，通过原子力显微镜（AFM）、透射电子显微镜（TEM）和动态光散射（DLS）探测，PffBT4T聚合物强烈聚集，形成厚度为几纳米、长度为数百纳米的织物结构。根据温度相关的SANS测量，在高于聚集到溶解链转变温度的高温下，PffBT4T完全溶解，并采用半柔性线圈构象，PffBT4T-C8C12的持久性长度为3.1 nm，PffBT4T-C9C13的持久性长度略有增加，为3.4 nm。与PffBT4T-C8C12相比，PffBT4T-C9C13更长的侧链也会导致更少的聚集焓增益。这项工作提供了CPs的解决方案结构操纵策略，从而将启发CPs的分子设计和处理协议朝着更高性能的电子器件方向发展。

关键词：共轭聚合物、小角中子散射、链构象、聚合物聚集、侧链长度

Variable-Temperature Scattering and Spectroscopy Characterizations for Temperature-Dependent Solution Assembly of PffBT4T-Based Conjugated Polymers

Zhiqiang Cao, Guorong Ma, Mingwan Leng, Song Zhang, Jihua Chen, Changwoo Do, Kunlun Hong, Lei Fang, and Xiaodan Gu*

School of Polymer Science and Engineering, The University of Southern Mississippi, Hattiesburg, Mississippi 39406, United States

Cite this: ACS Appl. Polym. Mater. 2022, 4, 5, 3023–3033

Publication Date: February 9, 2022

https://doi.org/10.1021/acsapm.1c01511

Abstract

The solution structure of conjugated polymers (CPs) from which the films are cast is critical for tailoring the thin-film morphology thus device performance. Here, we used multimodal variable-temperature scattering and spectroscopy tools to fully quantify the solution assembly of poly[(5,6-difluoro-2,1,3-benzothiadiazol-4,7-diyl)-alt-(3,3‴-dialkyl-2,2′;5′,2″;5″,2‴-quaterthiophen-5,5‴-diyl)] (PffBT4T) polymers with varying side-chain lengths at different assembly temperatures. The conformational and aggregation behaviors for PffBT4T-based CPs were found to be very sensitive to both temperature and side chain length using ultraviolet–visible (UV–vis) spectroscopy, nuclear magnetic resonance (NMR) spectroscopy, dynamic light scattering (DLS), and small-angle neutron scattering (SANS). We found that with slightly increasing side chain length from 2-octyldodecyl (C8C12) to 2-nonyltridecyl (C9C13), PffBT4T-based CPs show a significant decrease in aggregation-to-dissolved chain transition temperature (10 °C), degree of aggregation, enthalpy change of aggregation, and size of the aggregates in solution. At room temperature, PffBT4T polymer strongly aggregated to form fabric structure with the film thickness of a few nanometers in thickness and hundreds of nanometers in length, as probed by atomic force microscopy (AFM), transmission electronic microscopy (TEM), and dynamic light scattering (DLS). At the elevated temperature above the aggregation-to-dissolved chain transition temperature, PffBT4T is fully dissolved and adopts a semiflexible coil conformation with the persistence length of 3.1 nm for PffBT4T-C8C12 and a slightly increased persistence length of 3.4 nm for PffBT4T-C9C13, according to temperature-dependent SANS measurements. Longer side chains of PffBT4T-C9C13 also lead to less aggregation enthalpy gain compared with PffBT4T-C8C12. This work provides a solution structure manipulating strategy of CPs and thus will inspire the molecular design and processing protocols of CPs toward higher performance electronic devices.

KEYWORDS: conjugated polymers, small-angle neutron scattering, chain conformation, polymer aggregation, side-chain length

来源：《ACS Applied Polymer Materials》

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