Rubber aging at the microscopic scale

点击翻译按钮获取中文摘要

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.