Atomistic and coarse-grained simulations reveal increased ice nucleation activity on silver iodide surfaces in slit and wedge geometries

Abstract

Abstract. Ice clouds can form at low and moderate supercooling through heterogeneous ice nucleation on atmospheric particles. Typically, the nucleation requires active sites with special chemical and physical properties, including surface topology and roughness. This paper investigates microscopic mechanisms of how combinations of confinement by the surface topology and lattice match induced by the surface properties can lead to enhanced ice nucleation. We perform molecular dynamics simulations using both atomistic and coarse-grained water models, at very low supercooling, to extensively study heterogeneous ice nucleation in slit-like and concave wedge structures of silver-terminated silver iodide (0001) surfaces. We find that ice nucleation is greatly enhanced by slit-like structures when the gap width is a near-integer multiple of the thickness of an ice bilayer. For wedge systems we also do not find a simple linear dependence between ice nucleation activity and the opening angle. Instead we observe strong enhancement in concave wedge systems with angles that match the orientations of ice lattice planes, highlighting the importance of structural matching for ice nucleation in confined geometries. While in the slit systems ice cannot grow out of the slit, some wedge systems show that ice readily grows out of the wedge. In addition, some wedge systems stabilize ice structures when heating the system above the thermodynamics melting point. In the context of atmospheric ice-nucleating particles, our results strongly support the experimental evidence for the importance of surface features such as cracks or pits functioning as active sites for ice nucleation at low supercooling.

Characterizing Surface Ice-philicity Using Molecular Simulations and Enhanced Sampling

“…22,24,[59][60][61][62][63][64][65] Because the ability of a surface to nucleate ice depends primarily on its ice-philicity, we hope that our generalization of the SWIPES method will shed light on the molecular underpinnings of heterogeneous ice nucleation. For example, SWIPES could be used to quantify the ice-philicity of realistic surfaces, such as AgI, whose crystal planes have shown differing abilities to nucleate ice, [22][23][24][66][67][68] or clay minerals, such as K-feldspar, mica or kaolinite, which are of interest due to their role in cloud formation, 2,4,17,65 and could also be used to interrogate the role of dissolved ions in influencing surface ice-philicity. [69][70][71] Because SWIPES can be used to quantify the ice-phobicity of extremely poor ice nucleators, we believe that this method could also inform the design of materials or surface coatings for mitigating the formation of ice or frost.…”

“…It will be particularly interesting to explore the role of surface texture in further amplifying surface ice-phobicity akin to that observed in superhydrophobic surfaces. 6,68,[73][74][75] We note that SWIPES is not limited to characterizing surface ice-philicity, and the underlying methodological framework could also be used to characterize the preference of a surface for a generic crystal relative to its melt. For example, surfaces play an important role in nucleating clathrates, [76][77][78] and the discovery of surfaces capable of inhibiting the nucleation of gas hydrates could have important implications for the oil and natural gas industry.…”

Molecular simulations reveal that heterogeneous ice nucleation occurs at higher temperatures in water under capillary tension

“…The ice nucleation rate in water can be effected by confined geometries (Cao et al, 2019;Roudsari et al, 2022). When analyzing the increase in freezing temperature within the water capillary bridges, we need to disentangle the effects of confinement from the effects of Laplace pressure.…”

Deposition freezing, pore condensation freezing and adsorption: three processes one description?

“…Heterogeneous ice nucleation is thought to occur on so called ice nucleation active sites (INAS) whose nanoscale properties -both chemical and structural -enhance freezing of adsorbed clusters , whereas other locations that collect precritical clusters might have an opposite effect. For instance, ice nucleation is suppressed on molecularly rough or curved graphene (Lupi et al, 2014a), in wedge-shaped pores of black carbon (Bi et al, 2017) or AgI (Roudsari et al, 2022) for specific wedge angles which block the formation of initial ice embryos. Small steps and edges also alter IN activity of multiple surfaces (Roudsari et al, 2022).…”

“…For instance, ice nucleation is suppressed on molecularly rough or curved graphene (Lupi et al, 2014a), in wedge-shaped pores of black carbon (Bi et al, 2017) or AgI (Roudsari et al, 2022) for specific wedge angles which block the formation of initial ice embryos. Small steps and edges also alter IN activity of multiple surfaces (Roudsari et al, 2022). For ice-nucleating proteins, both their length and the lateral distance between the aggregate chains alter ice nucleation rates (Qiu et al, 2019), the latter in a non-monotonous way.…”