基于裂缝-褶皱协同作用的柔性力敏复合材料的构筑及其刺激-响应机理研究

Flexible strain sensing composites have wide potential applications in national key development fields, such as energy, environment, medical treatment and spaceflight fields, etc. The relevant studies have shown that it is difficult to balance the sensitivity and stability with the strain sensing range of flexible strain sensing composites, which are restricted mutually due to the influence of the material microstructure. Crack based flexible strain sensing composites have remarkable sensitivity, while the strain sensing range is restricted by the crack propagation mechanism. Wrinkle based flexible strain sensing composites possess perfect conductive network, superior response stability and very wide strain sensing range but a very low response sensitivity. Herein, combining the advantages of the two composites, a novel strain sensing composites graphene/thermoplastic polyurethane/polydimethylsiloxane with both crack and wrinkle microstructure will be fabricated to overcome the above restriction relations by using a subtended bending-tension method in this proposal. Combining the finite element stress analysis and material morphology observation, the generation and competition mechanism of cracks and wrinkles in the composites will be investigated, and the composites microstructure will be tuned efficiently. The synergistic conductive mechanism based on crack propagation and tunneling effect will be discussed. The response mechanism under the stress field stimuli and the relationship between the response and the evolution of composites microstructure will be studied. A model will be built with respect to the relationship of composites microstructure and responsive behaviors under mechanical stimuli to achieve synergetic tuning of the strain sensing properties. This project will provide a theoretical basis for the key scientific issues of flexible strain sensing composites, which are used for astronaut elbow motion monitoring and the tension tests for spacesuit backpack fastening belt.

柔性力敏材料在能源、环境、医疗、航天等领域有广泛应用前景，但材料的响应度、稳定性和应变范围等几个关键性能参数受结构影响而相互制约，难以兼顾。裂缝式力敏材料具有极高的灵敏度，但受裂纹扩展机制限制，应变范围有限(<30%)；褶皱式力敏材料导电网络完善，具有优异的响应稳定性和宽应变响应范围，但灵敏度很低。本项目拟将二者优势协同，采用对向弯折拉伸法制备兼具裂缝和褶皱结构的石墨烯/热塑性聚氨酯/聚二甲基硅氧烷柔性力敏材料，克服上述制约关系。拟结合有限元受力分析和材料形态结构观察，探讨裂缝和褶皱的生成和竞争机制，并对材料微观结构进行调控。探明体系基于裂纹扩展机制和隧道效应的协同导电机理，研究材料在应力外场中的刺激-响应机制及其与微结构演变间关系，构建微观结构-刺激-响应关系模型，实现材料力敏性能的协同调控。项目将为航天员肘部运动监测及航天服背包拉紧带张力测试所需柔性力敏材料的关键科学问题提供理论基础。

导电高分子复合材料（Conductive polymer composites，CPCs）由导电填料与高分子基体复合制备而成。CPCs在应力、温度、气体、液体等外场的作用下，体系中导电填料位置发生改变，材料电阻发生变化，从而表现出丰富的响应行为。这其中，CPCs在应力场中所表现出的响应行为，因在可穿戴器件、柔性电子皮肤等领域的应用而受到研究者的广泛关注。CPCs应变传感性能的响应范围，灵敏度和稳定性几个关键性能参数之间相互制约，极难兼顾。本项目制备了兼具裂纹-褶皱结构的石墨烯（GNPs）/热塑性聚氨酯（TPU）/聚二甲基硅氧烷（PDMS）CPCs，基于褶皱结构获得了高的拉伸应变测试范围，基于裂纹结构获得了高的灵敏度（GF=150）。其中，特殊的裂纹-褶皱结构通过自制的压力牵引装置制备而成。项目对复合材料导电层的微观形貌进行了详细分析，发现材料表面的裂纹及褶皱结构具有高的取向性，且分布较为均匀。利用偏光显微在线观察了拉伸过程中裂纹演化的过程。通过本方法制备的柔性拉伸应变传感材料拥有稳定的GF，这对于材料通过GF和电信号来测定材料实际应变大小具有重要意义。该应变传感材料在经受拉伸力时，存在垂直于拉伸方向的应力作用，导致裂纹突出部位发生错位现象，在回复过程中突出交错的裂纹结构能提前接触，形成新的导电通路，该传感材料因此在很大程度上消除了响应的滞后效应。在循环拉伸实验中，通过对不同加工参数制备的复合膜、应变大小的影响等分别进行测定，发现加工条件的施加压力为2 kPa时，材料表现出最佳的响应性能；材料对不同的应变具有不同的响应度，这说明该传感材料可以有效地测量不同材料的应变变化；材料在经受20000次拉伸-回复循环后，依然保持与初始状态几乎相同的电阻值，即材料具有优异的耐久性和响应稳定性；材料的响应时间为90 ms。基于本材料组装的传感器在人体运动监控中表现出良好的在线监测性能。本研究对传感性能优异的电阻型导电应变敏感复合材料的设计制备具有重要意义，材料在医疗健康及航天等领域具有一定的应用前景。