In order to develop excellent polymer materials, it is necessary to understand the functions required for the materials and design molecular structures, compounding, and so on, based on the logical understanding the mechanisms to make the functions appear. In the polymer materials, the hierarchical structures ranging from atomic level to nano and micron scale are formed in which various structures such as crystal structure, cross-linked network structure, and phase separation structure exist. Furthermore, when different materials from polymers such as carbon black, silica, fibers are compounded, the hierarchical structures formed by the different materials themselves and structures at the interfaces between the polymers and the different materials are formed. The origins of the polymeric materials' functions are the above-mentioned structures themselves and the creation of excellent polymeric materials is realized only by precisely controlling them. Development of quantum beam technology such as synchrotron radiation X-ray and neutron in recent years have brought dramatic improvement of evaluation on these structures not only in the academic fields but also in the industrial fields. We can clarify the mechanisms to make the functions appear, which could not be clarified by in-house equipment alone, by using the quantum beams. Some research by the quantum beams are introduced in this report.
We developed a thermoplastic elastomer by blending symmetric polystyrene-block-polyisoprene-block-polystyrene (SIS)and asymmetric SIS block copolymer. This polymer blend is promising as an elastic film because it has superior physical properties, such as high modulus and recoverability, compared to symmetrical SIS homopolymers which have been used as adhesives. In order to elucidate the reasons for such excellent physical properties, its structure was investigated by time-resolved small angle X-ray scattering, transmission electron microscope observation, and SCF simulation in stretching process. In the film made by pressing close to industrial processing, the characteristic structural change of the styrene domain was observed with time-resolved small angle X-ray scattering. Furthermore, it was also found that the processing conditions have a strong influence on the phase separation structure.
We analyzed the distribution of silica particles dispersed in an elastomer under deformation by reverse Monte Carlo (RMC) modelling. Using our RMC code, we can analyze a large system with many particles on a desktop PC. The code is effective for analyzing a system having a hierarchical structure like a rubber material. Ultra small angle X-ray scattering (USAXS) measurements under elongation by a bulge tester were performed on a silica-filled elastomer. The RMC modelling of USAXS data revealed the modification of the particle distribution in three dimensions. It was observed in the unstretched state that large sparse and dense parts formed, in terms of the particle dispersion, while these distinct regions disappeared on elongation. Furthermore, pair distribution function and interparticle angular distribution suggested that the dense regions show a structural order similar to a liquid metal, and that this ordering decreases due to elongation.
The dispersion state and aggregate structure of carbon black (CB) in polystyrene (PS) composites prepared by solvent casting the suspensions in different dispersion media: tetrahyrdrofuran, chloroform, and toluene, were investigated by transmission electron microscopy, and ultrasmall-angle and small-angle X-ray scattering (USAXS and SAXS). The macroscopic dispersion state of CB in the solvent-cast films reflects the dispersion stability of the suspensions in the PS solutions with the different dispersion media. The mass and surface fractal dimensions, Dm and Ds, of CB in PS were evaluated by applying the Beaucage unified equation to combined profiles of USAXS and SAXS. The evaluated values of Dm tend to exhibit a increment for the composite prepared by dispersion media with lower CB dispersibility in suspension, while the Ds values are clearly lower than that for the CB powder due to the effects of physical adsorption of the polymer on the CB surface. The viscoelastic moduli of the melt composites below and above the percolation limit varied with the dispersion medium, reflecting the difference in the macroscopic dispersion state and aggregate structure of CB in PS.
In this paper, as an example of the structural analysis of silica filler in rubbers by synchrotron small angle X-ray scattering, we show the application to end-modified styrene butadiene rubber (SBR) for fuel-efficient tire. The distribution of particle size of silica aggregates can be obtained by the analysis of scattering profile, and it is shown that radius of silica aggregate is smaller and distribution of particle size is narrower in end-modified SBR than in non-modified SBR. Deformation behavior of silica aggregates during elongation reveals to be different between modified and non-modified SBR by the simultaneous ultra-small angle X-ray scattering and stress-strain curve measurement. We have found the difference of mechanism of stress-strain curve between modified and non-modified SBR by the computer simulation using the results of ultra-small angle X-ray scattering experiment.