Interfacial Regulation of Wettability and Layered Bottom-Up Crystallization of Graphene-Supported Ni Nanodroplets

The solidification behavior of metallic nanodroplets on 2D material surfaces is critical for fabricating metal/carbon composites and regulating nanocrystalline microstructures. Using molecular dynamics simulations, we investigated the effect of Ni-C interfacial interaction strength on rapid solidification of graphene-supported Ni nanodroplets. We systematically analyzed wetting, thermal crystallization, local structure, crystallization distribution, and FCC/HCP layered enrichment. Stronger interactions reduce the contact angle and increase interfacial contact atoms, promoting droplet spreading and enlarging the Ni/graphene contact area. Average potential energy shifts upward in both onset and termination temperatures, implying enhanced coupling enables crystallization at elevated temperatures. Structural analysis shows weak interactions yield non-directional nucleation and growth, whereas strong interactions induce ordered structures near the interface that subsequently extend upward, exhibiting interface-associated bottom-up crystallization. The highest close-packed fraction resides in the middle of the nanoparticles, indicating that interface-induced crystallization, interfacial constraint, and free-surface effects jointly cause spatial nonuniformity. Overall, Ni-C interactions reshape the crystallization pathway, resulting in spatially nonuniform close-packed ordering and FCC/HCP layered enrichment in the final nanoparticle.