CAREER: Illuminating Interfacial Mechanics: Utilizing Mechanophores to Visualize Mechanical Performance at Soft Matter Interfaces

聚合物基复合材料的整体性能与界面的强度直接相关。填充弹性体，如汽车轮胎中的合成橡胶，依赖于界面的强度将应力从较软的橡胶基质转移到较硬的炭黑颗粒中，以提高其韧性并减少磨损。在纤维增强聚合物基复合材料（例如环氧树脂中的玻璃纤维）中，界面的韧性再次决定了系统的总体机械性能。直接和主动监测的界面应力传递机制导致更好地了解界面强度，接触几何形状和材料性能对复合材料失效的影响。减少故障和更强复合材料的潜力对美国的繁荣和持续经济增长至关重要。机械响应荧光分子，称为mechanophores，将安装在复合材料界面实验观察界面应力传递。在加载期间来自该标记物分子的荧光是局部界面状态的直接指示剂。该学院早期职业发展（CAREER）奖的研究提供了对界面机械载体激活的基本理解，并将为开发一类新的分子传感器提供设计原则，该传感器可以报告聚合物基复合材料界面损伤的真实的时间反馈。当该技术在现场部署时，可以延长风力涡轮机叶片和航空航天部件的使用寿命，并通过早期检测界面缺陷和应力集中来防止灾难性故障。机械载体是一类新型的刺激响应材料，它们在受到机械刺激时发生分子异构化或结构重排。在这里，二聚蒽将共价键合在二氧化硅和聚（二甲基硅氧烷）的界面处。当界面分离发生时，二聚体将在前进的裂纹的两侧分离成两个荧光蒽分子。与激光扫描共聚焦显微镜结合的接触力学粘附实验能够原位监测界面韧性（通过垂直载荷、位移和接触面积量化），同时具有机械活性团的荧光激活响应。利用非线性内聚区模型的有限元分析将提供对二氧化硅/硅氧烷界面处的复杂应力状态的深入了解。通过这项研究，将对影响界面损伤传感器激活的材料特性和几何参数有一个基本的了解。该奖项反映了NSF的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为是值得支持的。

The overall performance of polymer matrix composites is directly tied to the strength of the interface. Filled elastomers like the synthetic rubber in car tires rely on the strength of the interface to transfer stress from the softer rubber matrix into the stiffer carbon black particles to enhance their toughness and reduce wear. In fiber reinforced polymer matrix composites (e.g. glass fiber in epoxy), the toughness of the interface again determines the overall mechanical properties of the system. The directly and actively monitored interfacial stress transfer mechanism leads to a greater understanding of the impact of interfacial strength, contact geometry, and materials properties on composite failure. The reduction in failure and potential for stronger composites are critical to US prosperity and continued economic growth. Mechanically responsive fluorescent molecules, termed mechanophores, will be installed at composite interfaces to experimentally observe interfacial stress transfer. Fluorescence from this marker molecule during loading is a direct indicator of the local interfacial state. This Faculty Early Career Development (CAREER) award's research provides a fundamental understanding of the activation of interfacial mechanophores and will inform design principles towards the development of a new class of molecular sensors that can report real time feedback on interfacial damage in polymer matrix composites. When this technology is deployed in the field, service life of wind turbine blades and aerospace components could be extended and catastrophic failure prevented through early detection of interfacial defects and stress concentrations. Mechanophores are a new class of stimuli-responsive materials that undergo a molecular isomerization or structural rearrangement in response to a mechanical stimulus. Here, dimerized anthracene will be covalently bound at the interface of silica and poly(dimethyl siloxane). As interfacial separation occurs, the dimers will separate into two fluorescent anthracene molecules on both sides of the advancing crack. Contact mechanics adhesion experiments coupled with laser scanning confocal microscopy enables in situ monitoring of the interfacial toughness (quantified through vertical load, displacement, and contact area) simultaneously with the fluorescent activation response of the mechanophore. Finite element analysis that utilizes nonlinear cohesive zone models will provide insight into the complex stress state at the silica/siloxane interface. A fundamental understanding of the materials properties and geometric parameters that influence the activation of interfacial damage sensors will be achieved through this research.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.