As grinding progresses, powders exhibit high surface activity due to the generation of ions and radicals, and interfacial effects become pronounced. Mechanochemical reactions that effectively utilize this surface activity have been applied to the synthesis of functionalized powders. In this study, a mechanochemical polymerization process was carried out continuously modifying the surface of silica particles by grinding silica sand in the presence of methyl methacrylate (MMA) using a dry bead mill. The effects of grinding conditions on the MMA conversion, particle size distribution, specific surface area, and chemical composition were investigated. As a result, the possibility of continuously producing surface-modified particles with polymer coatings accompanied by fine grinding was demonstrated. Furthermore, it was confirmed that optimizing the milling atmosphere and grinding conditions is crucial for improving the efficiency of polymer-modified powder production in this process.

This article reviews recent progress in stress visualization techniques using photoelastic nanocrystal suspensions and soft elastic gels. These materials exhibit stress-induced birefringence, enabling full-field and non-invasive measurement of flow-induced and contact-induced stresses. First, flow-induced birefringence in rectangular channel flows is introduced, highlighting how phase retardation and azimuth reveal shear-stress concentration near walls and its dependence on flow rate. Second, photoelastic tomography using soft gels is presented for both static and dynamic Hertzian contact, demonstrating reconstruction of all stress components and impact-force scaling. Third, stress fields around a settling solid sphere are visualized experimentally for the first time, providing quantitative datasets for particle–fluid interactions. A machine-learning-based reconstruction (PICED) is also discussed as an emerging approach for recovering three-dimensional stress tensors. These techniques offer new opportunities for analyzing powder-handling processes involving slurry transport, particle impact, and particle–wall interactions.