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强度直接相关。填充弹性体，如汽车轮胎中的合成橡胶，依靠界面的强度将应力从较软的橡胶基质转移到较硬的碳黑颗粒中，以增强其韧性和减少磨损。在纤维增强聚合物基复合材料(如环氧玻璃纤维)中，界面的韧性再次决定系统的整体机械性能。直接和主动监测的界面应力传递机制使人们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破坏的影响。故障的减少和更坚固复合材料的潜力对美国的繁荣和持续的经济增长至关重要。机械响应的荧光分子，称为机械团，将被安装在复合材料界面上，以实验观察界面应力传递。在负载过程中来自该标记分子的荧光是局部界面状态的直接指示器。该学院早期职业发展奖(CAEREAR)的研究提供了对界面机械团激活的基本了解，并将为开发新型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中界面损伤的实时反馈。当这项技术在现场部署时，可以通过及早检测界面缺陷和应力集中来延长风力涡轮机叶片和航空航天部件的使用寿命，防止灾难性故障。机械团是一类新型的刺激响应性材料，在机械刺激的作用下会发生分子异构化或结构重排。在这里，二聚菲将共价键合在二氧化硅和聚二甲基硅氧烷的界面上。当界面分离发生时，二聚体将在前进的裂缝两侧分离成两个荧光菲分子。接触力学附着力实验与激光扫描共聚焦显微镜相结合，可以在机械量荧光激活响应的同时，对界面韧性(通过垂直载荷、位移和接触面积进行量化)进行现场监测。利用非线性凝聚区模型的有限元分析将提供对二氧化硅/硅氧烷界面处复杂应力状态的洞察。通过这项研究，将实现对影响界面损伤传感器激活的材料属性和几何参数的基本了解。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

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.