X-ray Scattering technique is a powerful method to analyze the structures of soft-materials in the order of 0.1 nm to 1,000 nm. Here we present the basics of X-ray scattering and how we can apply this method to the rubber systems including complex hierarchical structures.

The nanoscopic morphology of soft material thin films such as plastic, elastomer and rubber films has been successfully analyzed by grazing-incidence small-angle X-ray scattering (GISAXS). Recently, advanced GISAXS techniques for analysis for surface-, volume-, and material (element)-sensitive method has been reported. Resonant (anomalous) GISAXS and GISAXS with low X-ray photon energy (tender X-rays and soft X-rays near K-edge of carbon) allows probing a complex nanomorphology with those sensitivity. In this report, principle of GISAXS will be outlined simply and advanced GI-SAXS methods will be picked up to open for discussion on new possibility of structure analysis.

Usefulness of recent synchrotron X-ray-absorption fine structure (XAFS) measurements is described for characterization of network structures of vulcanizates. The first example is related to the formation of two-phase network morphology in vulcanizates. In situ zinc K-shell X-ray-absorption near-edge structure (XANES) measurement during vulcanization is reported to support the simultaneous progress of two sulfur cross-linking reactions in the N-(1,3-benzothiazol-2-ylsulfanyl) cyclohexanamine accelerated systems under the presence of ZnO or zinc stearate. The second is a study on in situ zinc K-shell XAFS measurement for analyzing a novel intermediate, which was generated from ZnO and stearic acid during vulcanization. The intermediate [Zn₂(μ-O₂CC₁₇H₃₅)₂]²⁺(OH⁻)₂ is newly found as an active catalyst for the sulfur cross-linking reaction. The third is a study on sulfur K-shell XANES measurement to determine characteristics of sulfidic linkages in vulcanizates which were prepared by the accelerated vulcanizations using the new intermediate. The disulfidic linkage is reported to be dominantly generated in the systems. Finally, a study on scanning transmission X-ray microscopy, which provides the XANES spectra in 2D mapping, is introduced. The XAFS analysis may be a powerful tool for characterization of rubber materials.

Hard X-ray photoelectron spectroscopy (HAXPES) is a powerful tool which can observe chemical states of composite elements, including rubber specimens, from the surface to the internal layer without destruction. Furthermore, utilizing angle-resolved photoelectron spectroscopy (ARPES), the chemical states distribution of the elements in bulk and surface regions can be analyzed. In this report, two studies applied HAXPES and ARPES are introduced. The first part is a direct observation focusing on the buried adhesive interface between rubber and brass plate by using HAXPES and ARPES techniques. The chemical state distribution of sulfur compounds in the interface layer is investigated to clarify the thermal degradation mechanism of the adhesion strength. The second part is a study investigating chemical states and kinetics of sulfur in rubber compound. Density variation of S-C and S-S species with heating time is observed in both bulk and surface regions of rubber specimens to discuss rubber vulcanization process.

To elucidate the nature of the mechanical properties of rubber composite, it is necessary to investigate the 3D structure of polymers and fillers in rubber composite over a wide-size scale. We have utilized ultra-small-angle X-ray scattering to observe changes in the aggregate/agglomerate structure of nanoparticles in uniaxially stretched rubber.^{1), 2)} However, real-space 3D structural information cannot be directly obtained with a scattering technique. Therefore, the development of a real-space microscopy technique is required. X-ray imaging techniques have also been developed in association with advances in synchrotron X-ray technology. The advantages of X-ray imaging include a wider field of view, sub-micron-level spatial resolution and less damage to the specimen. In this study, the 3D structure of spherical silica particles and polymers in rubber composite was visualized with a higher spatial resolution using a Zernike-type phase contrast X-ray microtomography. This method improved the contrast of images and gave us an opportunity to investigate a detailed 3D-submicron scale configuration of fillers and polymers with a wide field of view. This method was proven to be a powerful tool to obtain the 3D structural configuration of soft materials.