Metal nanoparticles usually show different oxidation dynamics from bulk metals, which results in various oxide nanostructures because of their sizerelated surface effects. In this work, we have found and investigated the chain-like nucleation and growth of oxides on the aluminum nanoparticle (ANP) surface, using molecular dynamics simulations with the reactive force-field (ReaxFF). After nucleation, the chain-like oxide nuclei could stay on the ANP surface and continue growing into an oxide shell, extend outward from the surface to form longer oxide chains, or detach from the ANP to generate independent oxide clusters, which is highly dependent on the oxygen content, temperature, and nanoparticle size. Our results emphasize the complicated interplay between the surface structure of nanoparticles and the environmental conditions in determining the formation of oxides, which provides insights into the atomic-scale oxidation mechanism of metal nanoparticles.
Molecular dynamics simulations were performed to investigate the wetting and coalescence of liquid Al and Pb drops on four carbon-based substrates. We highlight the importance of the microstructure and surface topography of substrates in the coalescence process. Our results show that the effect of substrate on coalescence is achieved by changing the wettability of the Pb metal. Additionally, we determine the critical distance between nonadjacent Al and Pb films required for coalescence. These findings improve our understanding of the coalescence of immiscible liquid metals at the atomistic level.
Surfaces designed so that liquid metals do not stick to them but instead rebound as soon as possible have received considerable attention due to their significant importance in many practical technologies. We herein design a ridge structure that can induce the drop to rapidly rebound through the combination effect of centre-drawing recoil and the resulting faster retraction velocity. The suitable sharp-angle of the ridge for minimizing the contact time is determined as 20-30°. Further analysis reveals that multi-ridge structure or two-ridge structure with gaps can reduce more contact time. We also highlight the role the impact velocity played in minimizing the contact time, which has been a neglected parameter previously. Our studies would open up a new way to reduce the contact time and control the bouncing dynamics of metal drops, which provides guidance for some potential applications, such as preventing splashing molten drops from depositing on clean surface.
The ability to predict and control the coalescence of droplets is of great importance for both industrial and technological applications, including 3D printing, micro-cladding, and self-assembly. Here, a textured surface decorated with nano-pillared arrays was designed and its arrangement density (f) was found to significantly affect the coalescence dynamics of droplets through changing their wettability. A large arrangement density f of the nano-pillared arrays would induce a Cassie wetting state for droplets, which supports the coalescence process. But when decreasing f to a value that produces a Wenzel wetting state, the coalescence is heavily impeded by the nano-pillars. However, a very small arrangement density f is also favorable for coalescence because the pinning effect resulting from the nano-pillars becomes ignored. More importantly, special substrates were well designed by nano-pillars with a density gradient in order to control the coalescence dynamics for some potential applications. This work helps to shed light on the coalescence dynamics of droplets on a microtextured surface modified with different arranged nano-pillars and thereby provides guidance on how to control their behaviors.
Molecular dynamics (MD) simulations are performed to investigate the wettability of liquid metal on the metal substrate. Results show that there exists different wettability on the different metal substrates, which is mainly determined by the interaction between the liquid and the substrate. The liquid metal is more likely to wet the same kind of metal substrate, which attracts the liquid metal to one side on the hybrid substrate. Exchanging the liquid metal and substrate metal has no effect on the wettability between these two metals. Moreover, the study of metal drop coalescing indicates that the metal substrate can significantly affect the coalescence behavior, in which the changeable wettability of liquid metal plays a predominant role. These studies demonstrate that the wetting behavior of liquid metal can be controlled by choosing the suitable metal substrate.
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