Rubber aging at the microscopic scale

橡胶轮胎是汽车供应链的关键组成部分，作为唯一接触道路的车辆部件，对车辆的安全性和燃油效率有很大贡献。根据最近的报道，轮胎在环境温度高的地区老化得更快。虽然氧化也被认为在老化现象中起着关键作用，但它只发生在轮胎与空气接触的最表层。由于基体橡胶的氧化和硬化不是导致轮胎老化的主要原因，因此将重点放在橡胶-填料界面上是合理的，因为填充橡胶的储存和耗散能都是强烈局部化的。界面现象的关键潜在成分是结合橡胶，它与基体橡胶以及邻近的填料接合。然而，粘合橡胶在材料性能和耐久性方面的多方面作用仍未得到解答。为了解决这一差距，交联炭黑填充的聚丁二烯和二氧化硅填充的聚丁二烯体系将被用作合理的模型。在实验室烤箱中人工老化模型填充橡胶将被用来模拟轮胎在使用中的自然老化。因此，为了了解驾驶条件下橡胶老化的机制，PI的团队将整合实验和计算的多尺度，互补的测量/分析，并为未来的交通运输提供必要的材料设计见解。通过学术界、工业界和国家用户设施的跨领域合作，该项目通过课程开发和研究生指导、加强本科生的研究培训以及在当地学校科学博览会上开展K-12外展活动，进一步促进了广泛的参与。PI将与PI所在研究所的职业中心合作，着手采取具体行动，改善代表性不足群体的征聘。由于基体橡胶的氧化和硬化不是轮胎老化的主要原因，因此将重点放在橡胶-填料界面上是合理的，因为填充橡胶的储存和耗散能都是强烈局部化的。界面现象的关键潜在成分是结合橡胶，它与基体橡胶以及邻近的填料接合。然而，粘合橡胶在材料性能和耐久性方面的多方面作用仍未得到解答。为了解决这一差距，交联炭黑填充的聚丁二烯和二氧化硅填充的聚丁二烯体系将被用作合理的模型。在实验室烤箱中人工老化模型填充橡胶将被用来模拟轮胎在使用中的自然老化。中子散射/光谱技术与同位素标记将提供深入了解基体橡胶中的结合橡胶的结构和动力学。此外，将进行粗粒度的分子动力学模拟，以补充实验结果并揭示实验无法获得的细节。同时，为了模拟在驾驶条件下旋转轮胎的老化，将进行振荡变形过程中的x射线光子相关光谱测量。实验将提供同时访问的时间和空间的解决结构和动态的填料网络结构通过绑定橡胶介导的桥梁。这些结果将允许建立以非破坏性方式测量内部橡胶破坏程度的微观标准。综合实验-计算方法以及模型橡胶将促进对老化橡胶结构-动力学-性能关系的理解，并获得丰富而复杂的橡胶物理和材料设计见解。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的智力价值和更广泛的影响审查标准进行评估，被认为值得支持。

PART 1: NON-TECHNICAL SUMMARYRubber tires are a key component of the automotive supply chains and, as the only vehicle part that touches the road, greatly contribute to vehicle safety and fuel efficiency. According to recent reports, tires age faster in regions with high ambient temperatures. While oxidation is also believed to play a critical role in the aging phenomenon, it only occurs at the topmost surface of a tire that is in contact with air. As oxidation and the hardening of a matrix rubber are not primarily responsible for tire aging, it is therefore reasonable to focus on the rubber-filler interface where both storage and dissipation energies of filled rubbers are strongly localized. The key underlying component of the interfacial phenomena is bound rubber that engages with the matrix rubber as well as adjacent fillers. However, the multifaceted role of bound rubber in material properties and durability remains unanswered. To address this gap, cross-linked carbon black filled polybutadiene and silica filled polybutadiene systems will be used as rational models. Artificially aging of model-filled rubbers in a laboratory oven will be utilized to simulate the natural aging of the tire in service. Thus, to understand the mechanism underlying rubber aging under the driving conditions, the PI's group will integrate experimental and computational multiscale, complementary measurements/analysis and derive necessary material design insight for future transportation. Through collaborations across fields in academia, industry, and national user facilities, this project further fosters a wide range of broadening participation through curriculum development and mentoring for graduate students, enhancement of research training of undergraduate students, and K-12 outreach activities at local school science fairs. The PI will embark on specific initiatives aimed at improving the recruitment of underrepresented groups in collaboration with the Career Center at the PI’s institute. PART 2: TECHNICAL SUMMARYAs oxidation and the hardening of a matrix rubber are not primarily responsible for tire aging, it is therefore reasonable to focus on the rubber-filler interface where both storage and dissipation energies of filled rubbers are strongly localized. The key underlying component of the interfacial phenomena is bound rubber that engages with the matrix rubber as well as adjacent fillers. However, the multifaceted role of bound rubber in material properties and durability remains unanswered. To address this gap, cross-linked carbon black filled polybutadiene and silica filled polybutadiene systems will be used as rational models. Artificially aging of model-filled rubbers in a laboratory oven will be utilized to simulate the natural aging of the tire in service. Neutron scattering/spectroscopy techniques with isotope-labeling will provide insight into the structures and dynamics of bound rubber buried in a matrix rubber. In addition, coarse-grained molecular dynamics simulations will be performed to complement the experimental results and unravel the details that are not accessible experimentally. In parallel, to mimic the aging of a rotating tire under a driving condition, in operando X-ray photon correlation spectroscopy measurements during oscillatory deformation will be conducted. The experiments will provide simultaneous access to temporally- and spatially resolved structures and dynamics of a filler network structure via bound rubber–mediated bridges. These results will allow the establishment of the microscopic criteria for measuring the degree of internal rubber failure in a non-destructive manner. The integrated experimental-computational approach along with the model rubbers will advance understanding of the structure-dynamics-property relationship of aged rubbers and derive rich and complex physics and material design insight on rubbers..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.