Wang Yang, Li Zhaofan, Niu Kangmin, Xia Wenjie, Giuntoli Andrea
Zernike Institute for Advanced Materials, University of Groningen, 9747 AG, Groningen, The Netherlands.
School of Materials Science and Engineering, University of Science and Technology Beijing, Beijing 100083, China.
Macromolecules. 2024 May 20;57(11):5130-5142. doi: 10.1021/acs.macromol.4c00232. eCollection 2024 Jun 11.
Understanding and predicting the mechanical and conformational properties of conjugated polymer (CP) thin films are a central focus in flexible electronic device research. Employing molecular dynamics simulations with an architecture-transferable chemistry-specific coarse-grained (CG) model of poly(3-alkylthiophene)s (P3ATs), developed by using an energy renormalization approach, we investigate the mechanical and conformational behavior of P3AT thin films during deformation. The density profiles and measures of local mobility identify a softer interfacial layer for all films, the thickness of which does not depend on or side-chain length. Remarkably, Young's modulus measured via nanoindentation is more sensitive to than for tensile tests, which we attribute to distinct deformation mechanisms. High- thin films show increased toughness, whereas longer side-chain lengths of P3AT resulted in lower Young's modulus. Fractures in low- thin films occur through chain pullout due to insufficient chain entanglement and crazing in the plastic region. Importantly, stretching promoted both chain alignment and longer conjugation lengths of P3AT, potentially enhancing its electronic properties. For instance, at room temperature, stretching P3HT thin films to 150% increases the conjugated length of P3HT thin films from 2.7 nm to 4.7 nm, aligning with previous experimental findings and all-atom simulation results. Furthermore, high- thin films display elevated friction forces due to the chain accumulation on the indenter, with negligible variations in the friction coefficient across all thin film systems. These findings offer valuable insights that enhance our understanding and guide the rational design of CP thin films in flexible electronics.
理解和预测共轭聚合物（CP）薄膜的力学和构象性质是柔性电子器件研究的核心重点。我们采用分子动力学模拟，借助一种通过能量重整化方法开发的、具有结构可转移化学特异性粗粒化（CG）模型的聚（3-烷基噻吩）（P3AT），研究了P3AT薄膜在变形过程中的力学和构象行为。密度分布和局部迁移率测量结果表明，所有薄膜都有一个较软的界面层，其厚度与 或侧链长度无关。值得注意的是，通过纳米压痕测量的杨氏模量对 的敏感度高于拉伸试验，我们将其归因于不同的变形机制。高 薄膜显示出韧性增加，而P3AT较长的侧链长度导致较低的杨氏模量。低 薄膜中的断裂是由于链缠结不足导致的链拔出以及塑性区域的 crazing 引起的。重要的是，拉伸促进了P3AT的链排列和更长的共轭长度，有可能增强其电子性能。例如，在室温下，将P3HT薄膜拉伸至150%会使P3HT薄膜的共轭长度从2.7纳米增加到4.7纳米，这与之前的实验结果和全原子模拟结果一致。此外，由于链在压痕上的堆积，高 薄膜显示出更高的摩擦力，且在所有薄膜系统中摩擦系数的变化可忽略不计。这些发现提供了有价值的见解，增强了我们的理解，并指导了柔性电子器件中CP薄膜的合理设计。
