Heterogeneous ice nucleation is one of the most common and important process in the physical environment. AgI has been proved to be an effective ice nucleating agent in the process of ice nucleation. However, the microscopic mechanism of AgI in heterogeneous ice nucleation has not been fully understood.Molecular dynamics simulations are applied to investigate the ability of which kinds of -AgI substrate can promote ice nucleation by changing the dipole of -AgI on the substrate, we conclude that the dipole of -AgI on the substrate can affect the conformation of ice nucleation. The surface ions with positive charge on the substrate may promote ice nucleation, while there is no ice nucleation founded on the surface ions with negative charge. -AgI substrates affect ice nucleation through adjust the orientations of water molecules near the surfaces.
Recently, ice with stacking disorder structure, consisting of random sequences of cubic ice (Ic) and hexagonal ice (Ih) layers, was reported to be more stable than pure Ih/Ic. Due to a much lower free energy barrier of heterogeneous nucleation, in practice, the freezing process of water is controlled by heterogeneous nucleation triggered by an external medium. Therefore, we carry out molecular dynamic simulations to explore how ice polymorphism depends on the lattice structure of the crystalline substrates on which the ice is grown, focusing on the primary source of atmospheric aerosols, carbon materials. It turns out that, during the nucleation stage, the polymorph of ice nuclei is strongly affected by graphene substrates. For ice nucleation on graphene, we find Ih is the dominant polymorph. This can be attributed to structural similarities between graphene and basal face of Ih. Our results also suggest that the substrate only affects the polymorph of ice close to the graphene surface, with the preference for Ih diminishing as the ice layer grows.
Heterogeneous ice nucleation has always been a hot research topic because of its fundamental importance to a variety of research areas, from climate to biology and from aviation to the energy industry. The formation of ice in the earth’s atmosphere depends on aerosols of various sources. As the main component of atmospheric aerosols, carbon particles composed of graphite have attracted much attention in heterogeneous ice nucleation. There is great variability in the freezing efficiency of ice induced by surface nanostructures, and the presence of surface defects, such as steps, can lead to the complex behavior of ice nucleation. In this work, molecular dynamics (MD) simulation was employed to investigate ice nucleation on graphite surfaces with the step structure. It was found that the graphite step with a real atomic structure reduced the freezing efficiency of surfaces, which was attributed to the large interfacial free energy between ice and the side face of the graphite steps. It was demonstrated by further investigations that the effect of nanogrooves consisting of step edges on ice nucleation was not only determined by the matching of groove width and ice lattice constant but also by the atomic structure of nanogrooves, shedding light on the study of control strategy of ice nucleation by surface nanostructures.
Recently, ice with the stacking disorder structure, consisting of random sequences of cubic ice (Ic) and hexagonal ice (Ih) layers, is reported to be more stable than pure Ih/Ic. While, due to a much lower free energy barrier of heterogeneous nucleation, in practice, the freezing process of water is usually controlled by heterogeneous nucleation which is triggered by an external medium. Herein, molecular dynamic simulations were carried out to explore the polymorph dependence of ice on the lattice structure of substrates. It turns out that, during the nucleation stage, the polymorph of ice nuclei can be severely altered by the graphene substrate, on which the Ih was found to occupy an absolute majority in new-formed ice. This can be attributed to the structure similarity between graphene and basal face of Ih. Besides the nucleation stage, our results suggest that the substrate can not affect the polymorph of ice which is far from the graphene surface. The polymorph selectivity of graphene to Ih will diminish with the growth of ice layer.
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