An international team of researchers have observed a phenomenon called virtual melting in colloidal crystals. They studied how it helps enable changes from one crystalline structure to another
Shear-induced structural transitions happen when the structure of a material changes due to the application of force. It’s a phenomenon observed in various systems, including metals like aluminium and iron, molecular crystals such as ice and quartz, and even the Earth’s mantle.
A better understanding of how it works could lead to an improvement in the processing and fabrication of materials with more control on defect formation.
Measuring microscopic processes like this is usually challenging because electron microscopy cannot resolve individual atoms’ motions in bulk solids, and the strong shear force makes things especially difficult.
Here, the researchers used colloidal crystals, allowing them to observe transitions at the single-particle level. As a soft material (one that can easily be deformed), colloid crystals are particularly well-suited for this type of study.
They found that under certain conditions, a liquid layer formed around the growing new crystal structure. This phenomenon is known as “virtual melting” because it occurs well below the effective melting temperature. This liquid layer facilitates the transition by reducing the strain energy at the interface between the old and new crystal structures.
Virtual melting has been proposed in theory and simulation, but had never been directly observed in experiments before. The team’s results not only represent the first experimental observation of this process but also help us to better understand under what circumstances it takes place.
The study has potential applications across various fields, including metallurgy, materials science, and geophysics. The concept of virtual melting could also provide new a new way of thinking about stress relaxation and phase transitions in other systems.