Group from the University of Tokyo achieves 890 nanosecond motion picture capture of fine particles and polymers in tire rubber

A research group led by Professor Yuji C. Sasaki of the Graduate School of Frontier Sciences at the University of Tokyo, Assistant Professor Masahiro Kuramochi of the Graduate School of Science and Engineering at Ibaraki University, and Director Hiroyuki Kishimoto of the Chemical Analysis Center in the Research & Development HQ at Sumitomo Rubber Industries, announced that they have successfully measured the movement of carbon particles and polymers (polybutadiene) in the composite material systems that make up tire rubber with an unprecedented time resolution of 890 nanoseconds. This measurement was achieved using the European X-ray Free-Electron Laser (European XFEL) in Hamburg, Germany. The movement of both components was found to change when the bonding states near their interface differed. This achievement is expected to contribute to the early diagnosis of rubber degradation and material development and was published in the Sept. 4, 2023 issue of Applied Physics Letters, a journal published by the American Physical Society.

Various factors, including structural characteristics at the molecular level, the dispersion of fine particles that make up the composite tire and the interactions between the components of the base polymer (polybutadiene), are involved in the grip and wear resistance performance of tires. Understanding molecular movement at the nanosecond-time scale is required to understand these relationships and enable accurate performance evaluations. However, this understanding is difficult to obtain using conventional techniques.

Sasaki and his colleagues developed a diffracted X-ray blinking (DXB) method based on monochromatic X-rays, which can accurately capture the internal motion of a single molecule using a biological molecule as a model.

In this study, the research group applied the DXB method to tire rubber. Focusing on carbon black (CB: 50−80 nanometers in diameter) and polybutadiene, the main components of tire rubber, X-ray measurements using the European XFEL observed each component with an unprecedented time resolution of 890 nanoseconds. The European XFEL, the world's most powerful X-ray free-electron laser facility, was constructed through cooperation among E.U. member states and is located on the Deutsches Elektronen-Synchrotron campus. The facility's ultra-bright X-rays have an extremely short pulse duration, thereby allowing for the ultra-fast analysis of material dynamics.

Time-resolved X-ray diffraction measurements and analyses were performed on two samples containing crystallized and noncrystallized CB with different rubber compounding states.

As a result, the research group successfully achieved the world's first simultaneous detection of the motion of each molecule related to the interaction between carbon and the polymer. The group performed autocorrelation analysis on the obtained diffraction patterns and extracted attenuation coefficients related to the motion of fine particles and polymer structures. According to the extracted attenuation coefficients, the motion of fine particles and polymer structures differed significantly between carbon and the polymer, which was attributed to differences in their high-speed environments and friction conditions at the molecular interface.

The introduction of the obtained information on molecular structural motion into degradation evaluations is expected to lead to the development of more rational and durable materials. This method can also be applied to other materials.

Journal Information
Publication: Applied Physics Letters
Title: Direct observation of 890 ns dynamics of carbon black and polybutadiene in rubber materials using diffracted x-ray blinking
DOI: 10.1063/5.0157359