空气相AFM单分子力谱研究P3HT晶体的纳米力学性质

The high-performance carrier mobilities of conjugated polymer semiconductors in nano and sub-micron scale derive from the ability to crystallize. And the mechanical properties of conjugated polymer crystals have a significant impact on their optoelectronic applications. Therefore, the study in their nano-mechanical properties in air is extremely critical and challenging. In the present project, poly(3-alkylthiophenes) (P3HT) crystals are researched as a model system by a combination of atomic force microscopy (AFM) and single-molecule force spectroscopy (SMFS). The projects are as follows:.1) By decreasing the adhesion force of water film, the AFM-based SMFS is extended to the investigation of polymer interactions in air..2) The effects of crystal structure, tempreture and medium on single-molecule melting and nanomechanics are investigated to reveal the mechanism of interface interaction and lattice interaction..3) We will establish the relationship between single-molecule and mesoscopic mechanical properties and also try to predict the bulk mechanical performance by single-molecule and mesoscopic mechanical properties in equilibrium..The performing of this project can establish a novel approach to investigate polymer nanomechanics in condensed state in air, and go one step further to represent the relationship between structure，crystallization and multi-scale mechanical properties, which could provide strategies for design and structural modulation of P3HT crystalline materials.

纳米及亚微米尺寸的光电聚合物晶体材料具有优良的电子传输性能，其力学稳定性是影响应用的重要因素，直接在空气相中研究其纳米力学性质是一个非常有意义而又充满挑战性的课题。本项目拟选取导电聚合物P3HT为模型体系，结合原子力显微镜的扫描定位和单个分子的操纵等功能，开展以下研究：第一，通过优化实验条件减小水膜粘附力的影响，建立空气相单分子力谱方法；第二，探索晶体结构、温度和介质对单分子熔融解链和纳米力学性质的影响，揭示界面相互作用和晶格相互作用的分子机制；第三，建立单分子和介观力学性质之间的关联，同时尝试利用单分子和介观平衡态力学性质来预测宏观力学性质。通过本项目的实施，不仅可以发展一种直接在空气相中研究高分子凝聚态纳米力学的方法，还将有利于建立结构、结晶性和多尺度力学性质之间的关系，为P3HT晶体材料的设计及结构调控提供参考。

本项目以聚3-己基噻吩（P3HT）纳米纤维为模型体系，探索了AFM单分子力谱、成像和三点弯曲在P3HT纳米纤维单分子力学和介观力学性质研究中的应用。首先系统研究了湿度、表面亲疏水性以及微悬臂弹性系数对单分子力谱实验的影响，建立空气相单分子力谱技术；通过使用带有沟槽的基底，建立了基于AFM操控单个纤维的方法。这些技术随后被用于研究微环境、层数、拉伸速率、拉伸方向等因素对P3HT纳米纤维单分子力学性质的影响。利用三点弯曲法和热形状波动分析法研究P3HT纳米纤维介观力学性质，并证明了π-π堆叠结构是导致P3HT纳米纤维机械性质各向异性的主要因素、片层堆叠对机械各向异性存在削弱效应等结论。同时揭示了P3HT纳米纤维形变过程中π-π滑移为动力学平衡过程、具有良好的可逆性、滑移与恢复具有滞后等分子机制。相关技术可以用于其它纳米纤维的研究，相关结果为光电材料的设计提供了理论依据。