宏观碳纳米材料聚集体黏弹性力学行为研究

To fully utilize the extraordinary mechanical, electrial and thermal properties of individual carbon naomaterials such as carbon nanotubes (CNTs) and/or graphene components at macroscopic level, over the past decade, great attention has been paid to fabriacte various macroscopic carbon nanomaterial based architectures. To date, various macroscopic architectures such as 1D CNT fiber, 2D CNT and/or graphene film (sheet), 3D CNT array, graphene sponge have been sucessfully fabricated in the lab, which have shown great potentional in structure materials, flexible electronic devices, energy dissipatoin, sensor and actuator fields. Considering its intrinsic nanometer-scale structure features, both individual CNT, graphene as well as its chemical derivates could be treated as novle type of polymer materials. Eariler works have shown that the 3D CNT array (sponge) behaved the polymer-like viscoelascity together with outstanding fatigue resistance, temperature-invariant, creep-resistance properties. However, the effect of microstructures on the viscoelastic behavior of architectures has not been deeply understood yet, in particular the contribution of microstructure deforamtion to the observed viscoleastic properties. Also theoretical analyses based on polymer viscoelasticity and molecular dynamics simulation have not been involved in this field yet. In this work, we focuse on the viscoelastic behavior of macroscopic 2D graphene film, 3D CNT sponge, and graphene sponge prepared by solution based self-assembly and CVD methods. Various dynamic mechanical testing methods, including creep test, stress relaxation test, temperature-dependent dynamic mechanical test, frequency- dependent dynamic mechanical test would be utilized to characterize the viscoelastic properties of various carbon nanomaterial based architectures. According to its specific microstrucutre features, novel dynamic mechanical testing methods are proposed to elucidate the unique mechanical properties of the macroscopic architectures. Specifically, the strain-hardening behaivor of graphene film in response to low-amplitude dynamic tension test, the super elasticity of the CNT sponge in response to cyclic compression test. The coressponding mechanical behavior of macroscopic architecutres will be compared with that of conventional polymeric materials such as polyurethane foam. In situ SEM-mechanical testing, micro Raman-mechanical testing and XRD testing are empolyed to illustrate the micro-structure evoluation of architecutres under deformaion process. With the help of molecular dynamics simulation as well as polymer viscoelastic theory,the relationship between microstructure and mechanical properties of architectures will be clarifed and confirmed experimentally. Finally, togeter with its excellent electric conductivity of carbon nanomaterial based architectures, we will explore its potential in artificial muscles and smart tissue fields.

碳纳米材料聚集体是宏观尺度实现碳纳米管、石墨烯单体优异功能特性的有效途径之一。近期研究表明碳管、石墨烯可以看做新型一维，二维高分子材料，其宏观聚集体也表现出类似于高聚物的黏弹性行为特征，预期在新型结构材料、柔性器件、轻质吸能材料等方面有潜在应用。但是聚集体微结构与宏观黏弹性力学行为间构效关系缺乏深刻认识。本项目以石墨烯薄膜、碳管海绵、石墨烯海绵为主要研究对象，开展黏弹性力学行为研究。根据聚集体不同微观结构特征，提出相应动态力学测试方法，揭示聚集体不同于传统高聚物独特的力学行为。借助高聚物黏弹性理论和分子动力学模拟解释力学行为，结合原位电镜、光谱等手段研究微结构演化过程和规律，阐明微结构因素及其演化过程对聚集体黏弹性行为影响，揭示聚集体力学性能跨尺度传递规律。通过微结构调控进行力学验证。结合碳纳米材料聚集体优异电等功能特性，探索在自增强自保护功能特性人工肌肉，人工智能软组织材料方面应用。

碳纳米材料具有优异光、电、力等物性，宏观聚集体是实现其优异功能特性的有效途径之一。碳纳米管、石墨烯作为新型高分子材料，预期其聚集体将表现出类似于高分子黏弹性力学行为特征。本面上项目开展了两类碳纳米材料聚集体结构设计、制备、黏弹性力学行为和功能特性研究。发展多种动态条件下力学测试方法，实现了：1)石墨烯薄膜动态自增强特性。结果表明自增强效应与层间作用力方式相关，例如GO/CS复合薄膜刚度动态振荡后可提升95%，杨氏模量到35.1±4.2 GPa，强度614.0±36.6 MPa，韧性1.7 MJ m-3；.2）碳纳米管海绵表现出优异结构稳定性、超弹性、−150–350 °C宽温度范围内稳定性、以及可以承受3.5 × 106 周期抗疲劳特性等；.3）碳纳米管/石墨烯杂化海绵表现出超弹性，在60%压缩应变下1000次循环加载后只观察到5% 应力松弛，明显优于单一石墨烯、碳纳米管海绵；.4）可拉伸变形达140%、负泊松比（- 0.5）石墨烯海绵；.借助多种原位表征技术手段研究了微结构演化过程和力学传递规律，揭示聚集体中结构和性能间构效关系，阐明力学性能跨尺度传递规律，其中界面作用方式及大小是决定结构稳定性关键性因素。结合材料自身导电特性，探索其在人工智能材料（自增强、仿皮肤压力传感器），可拉伸弹性导体等方面潜在应用前景。.为了深入探究界面作用力大小及其力学行为，以石墨烯作为模型体系，发展原位AFM-拉曼光谱-微孔鼓泡联用技术，实现了石墨烯层间以及与衬底界面剪切作用力大小实验测量, 研究结果表明石墨烯层间剪切应力在40 kPa左右，石墨烯与SiO2 层间作用力大概在1.64 MPa。由于石墨烯低面外刚度特征表现出类似于高分子材料柔性特征容易发生面外变形，借助薄膜力学理论，我们提出石墨烯面外变形（如鼓泡）解析解，并实验验证界面作用强弱对变形的影响。研究工作对于指导其它二维材料在应变工程方面的研究具有一定参考意义和指导价值。

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