结构可控碳纳米管复合膜的压阻响应机制研究

Carbon nanotube film has been demonstrated to possess great piezoresistive response, which has attracted a lot of attention. Recently, we investigated the microstructure and properties of an innovative carbon nanotube film by floating catalyst chemical vapor deposition method. This film exhibited excellent piezoresistive properties and much higher tensile strength than carbon nanotube buckypaper and other films. The excellent properties are found to be closely related to the network and nanotube bundle structures of the tested carbon nanotube film. In order to fully utilize the piezoresistive and mechanical properties for the application of strain sensor, the piezoresistive mechanism needs to be further studied. On the basis of our previous studies, this project mainly focuses on the piezoresistive mechanism and the synergistic effect between mechanical and piezoresistive properties. The electrical conductive mechanism of the structural units of carbon nanotube film, nanotube network and bundle, will be analyzed. The experiments about the influences of film microstructure, degree of nanotube alignment on the electrical resistivity and mechanical properties are designed to reveal the structure and property relationship. Piezoresistive response of nanotube film will be investigated under typical tensile and flexural loads. The gauge factor and strain relationship will be studied and the influences of strain rate, cyclic loading frequency will be analyzed. Based on the experimental results, physical model will be developed, which can be used to further optimize the microstructure and processing of nanotube film. This project is supposed to break through the limitation of traditional carbon nanotube buckypaper with low mechanical properties, and result in an innovative multi-functional material with both excellent mechanical and piezoresistive properties. This research will also explore a new direction for the strain sensor, and will contribute to the carbon nanotube application in structural health monitoring.

碳纳米管膜的压阻效应近几年引起了众多学者的关注，且有不少报道。但是申请者最近在研究气相沉积法制备的碳纳米管膜发现，该种膜在拉应力作用下，除了具有一般碳纳米管膜状材料的优良压阻效应外，其力学性能比一般碳纳米管膜状材料高几十倍。初步分析发现，该种膜的力、电特性与其内部碳纳米管网络和集束结构有关，明晰其中的作用机制，对于充分利用碳纳米管优异的功能和力学特性，开发新型应变传感材料具有重要指导意义。本项目即针对这一背景，深入研究气相沉积碳纳米管膜网络结构和集束结构的导电与力学强化机制，揭示碳纳米管堆积取向形态对其导电和力学性能的影响规律，以及外力作用下碳纳米管膜的压阻响应规律。在此基础上，对碳纳米管复合膜进行力、电效应协同设计，掌握高压阻应变系数高强碳纳米管复合膜压阻材料的制备方法，有效解决一般压阻碳纳米管膜力学性能低的难题，为开辟新型应变传感材料提供科学依据。

气相沉积碳纳米管膜具有优良的压阻效应和力学性能，本项目即针对该类碳纳米管膜压阻功能特性，深入研究其结构调节方法与导电机制，揭示碳纳米管膜和复合膜压阻响应主控机制，分析压阻效应对外力类型的敏感性及影响因素，在此基础上，实现协同力学性能与压阻响应的碳纳米管复合膜结构设计。研究结果表明，利用浮动催化气相沉积方法制备的碳纳米管膜厚度均匀且表面平整，通过收集速度控制、溶剂密实等方法实现了膜结构调控。随着温度升高，碳纳米管膜及其复合膜电阻率增大，表明该种催化剂交联共生的连续碳纳米管网络结构中本征电阻起主控作用。拉伸载荷作用下，碳纳米管膜电阻随应变增加而增大，采用乙醇辅助湿牵伸/热处理法可促进碳纳米管定向排列，成功制备出高取向致密化碳纳米管膜，压阻因子为13.2。在循环拉伸载荷和侧向压缩载荷作用下，碳纳米管复合膜均呈现正压阻效应；碳纳米管取向度、树脂含量、表面处理等对复合膜压阻特性具有显著影响，利用盐酸处理可使环氧复合膜压阻因子增至14.8。同时发现，复合膜压阻因子与基体模量大小正相关，碳纳米管/碳纳米管集束与树脂基体的强界面作用有助于提高压阻效应，且在低于玻璃化转变温度50°C以上可以获得稳定的压阻响应。研究结果为碳纳米管膜应变监测应用提供了科学依据。