The hierarchical structures of poly(styrene-ran-butadiene) (SBR) rubber vulcanized with sulfur in a swollen state were investigated by using the contrast-variation ultra-small-angle neutron scattering (USANS) and small-angle neutron scattering (SANS) techniques. The following three levels of hierarchical structure were found: (i) ZnO clusters surrounded by dense SBR networks of the order of 1000 Å in size, (ii) dense networks of SBR in the size range of 70–100 Å and (iii) a mesh size of the network of the order of 10 Å. In addition to the three kinds of structure, dense networks without ZnO of the order of 1000 Å were also observed. These last networks were formed by ZnO's reaction with sulfur. However, the ZnO clusters disappeared, which is associated with the diffusion of Zn.

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Small-angle X-ray scattering (SAXS) coupled with computed tomography (CT), denoted SAXS-CT, has enabled the spatial distribution of the characteristic parameters (e.g. size, shape, surface, length) of nanoscale structures inside samples to be visualized. In this work, a new scheme with Tikhonov regularization was developed to remove the effects of artifacts caused by streak scattering originating from the reflection of the incident beam in the contour regions of the sample. The noise due to streak scattering was successfully removed from the sinogram image and hence the CT image could be reconstructed free from artifacts in the contour regions.

The hierarchical structures of poly(styrene-ran-butadiene) (SBR) rubber/carbon black (CB) systems vulcanized with sulfur and ZnO have been clarified using anomalous small-angle X-ray scattering (ASAXS) near the Zn absorption edge. In the case of SBR/CB systems vulcanized with peroxide, it has been found previously that the hierarchical structures formed by CB consist of aggregates of primary particles and agglomerates of those aggregates with mass-fractal dimensions. However, to date the hierarchical structures in SBR/CB systems vulcanized with sulfur and ZnO have not been well investigated, despite being commonly used. This is because the strong scattering contrast of Zn prevents the quantitative analyses of the hierarchical structures of CB using X-ray scattering. In this study, the effects of Zn on the scattering intensity were eliminated and the structure factors of CB in SBR/CB systems were obtained using the ASAXS method. By extrapolating to the zero volume fraction of CB, the particle structure factor of the CB aggregates was estimated and it was found that the CB aggregates consist of closely packed CB primary particles. The presence of large particles of ZnO and particles of ZnS on the order of 10 nm in size is confirmed.

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