Even if a liquid is cooled below its melting point, the liquid state can be maintained under certain conditions. This state is called supercooling. Spraying fine particles of dry ice or silver iodide induces a phase change from supercooled droplets to ice grains. However, the mechanism by which crystallization seeds diminish supercooling is not well understood. Here, we captured the moment when a cluster, which is the smallest structural unit of a crystal, envelops a silver nanoparticle. As a result of observing the structure of a supercooled aqueous solution of a clathrate hydrate, we found that silver nanoparticles accelerate the formation of clusters, whereas the noble metals palladium, gold and iridium likewise form nanoparticles but do not promote crystallization. Our discoveries elucidate the mechanism of heterogeneous nucleation during a phase change in clathrate hydrates. We anticipate our discovery to be the starting point for the control of supercooling, a technique that can be applied to enhance the production efficiency and quality of manufactured products.

即使液体冷却到其熔点以下，在某些条件下仍可保持液态。这种状态称为过冷。喷洒干冰或碘化银的细颗粒会引起从过冷液滴到冰粒的相变。然而，结晶种子减少过冷的机制尚不清楚。在这里，我们捕捉到了簇（晶体的最小结构单元）包裹银纳米颗粒的时刻。通过观察笼形水合物的过冷水溶液的结构，我们发现银纳米粒子加速了簇的形成，而贵金属钯、金和铱同样形成了纳米粒子，但不促进结晶。我们的发现阐明了包合物水合物相变过程中异相成核的机制。我们预计我们的发现将成为控制过冷的起点，该技术可用于提高制造产品的生产效率和质量。