Aggregates of fine particles such as sand, flour, rice and beads are called powders or granular materials.Each grain is solid, but the aggregate behaves both liquid and solid.In particular, when a small amount of liquid is added to the powder or granular material, the liquid bridges between the sand particles (liquid cross-linking) and becomes much more robust than the dry powder or granular material.Silicone oil-coated silica sand for children's toys has little aging and can stably control mechanical properties.The research group focused on this sand as the third candidate for powder or granular material after dry and wet powder or granular material.

　Microscopic observation of the sand of this children's toy produced a liquid "thread", or liquid crosslink, when the coated particles were brought into contact with each other and then pulled apart.Therefore, we conducted an experiment to investigate the weight durability of the mixed sand by changing the mixing ratio of the two types of sand and changing the mechanical properties of the mixed sand.As a result, it was found that the weight durability of the sand was significantly increased when it was mixed with ordinary sand by about 2%.It is thought that the interacting coated sand forms a network and becomes stronger against its own weight.

　The discovery of powders with different flows and stability and their control are widely related to the development of novel materials such as concrete, civil engineering such as tunnel construction and landslide prevention, and disaster-related fields.The results of this research, which showed that the mechanical properties of sand can be controlled easily and stably, are expected to contribute to many of these fields.

Paper information:[J. Phys. Soc. Jpn.] Transition Behavior in Silicone-coated Sand Mixtures