Showing papers by "G. N. Patey published in 2016"
TL;DR: Molecular dynamics simulations of heterogeneous ice nucleation by kaolinite (001) surfaces suggest that surfaces can act as effective ice nuclei by matching one of the much larger set of planes that can be constructed by regular arrangements of hexagonal and cubic ice.
Abstract: Nucleation of ice by airborne particles is a process vital to weather and climate, yet our understanding of the mechanisms underlying this process is limited. Kaolinite is a clay that is a significant component of airborne particles and is an effective ice nucleus. Despite receiving considerable attention, the microscopic mechanism(s) by which kaolinite nucleates ice is not known. We report molecular dynamics simulations of heterogeneous ice nucleation by kaolinite (001) surfaces. Both the Al-surface and the Si-surface nucleate ice. For the Al-surface, reorientation of the surface hydroxyl groups is essential for ice nucleation. This flexibility allows the Al-surface to adopt a structure which is compatible with hexagonal ice, Ih, at the atomic level. On the rigid Si-surface, ice nucleates via an unusual structure that consists of an ordered arrangement of hexagonal and cubic ice layers, joined at their basal planes where the interfacial energy cost is low. This ice structure provides a good match to the ...
74 citations
TL;DR: Over the temperature range considered, the self-diffusion coefficients of the TIP3P model are much larger than those of TIP4P/2005 and those of real water, and it is shown that the entry rates are approximately inversely proportional to the shear viscosity of the bulk liquid, in agreement with the prediction of continuum hydrodynamics.
Abstract: We investigate pressure driven flow rates of water through a (6,6) carbon nanotube (CNT) for the TIP3P, SPC/E, and TIP4P/2005 water models The flow rates are shown to be strongly model dependent, differing by factors that range from ∼6 to ∼2 as the temperature varies from 260 to 320 K, with TIP3P showing the fastest flow and TIP4P/2005 the slowest For the (6,6) CNT, the size constraint allows only single-file conduction for all three water models Hence, unlike the situation for the larger [(8,8) and (9,9)] CNTs considered in our earlier work [L Liu and G N Patey, J Chem Phys 141, 18C518 (2014)], the different flow rates cannot be attributed to different model-dependent water structures within the nanotubes By carefully examining activation energies, we trace the origin of the model discrepancies for the (6,6) CNT to differing rates of entry into the nanotube, and these in turn are related to differing bulk mobilities of the water models Over the temperature range considered, the self-diffusion coefficients of the TIP3P model are much larger than those of TIP4P/2005 and those of real water Additionally, we show that the entry rates are approximately inversely proportional to the shear viscosity of the bulk liquid, in agreement with the prediction of continuum hydrodynamics For purposes of comparison, we also consider the larger (9,9) CNT In the (9,9) case, the flow rates for the TIP3P model still appear to be mainly controlled by the entry rates However, for the SPC/E and TIP4P/2005 models, entry is no longer the rate determining step for flow For these models, the activation energies controlling flow are considerably larger than the energetic barriers to entry, due in all likelihood to the ring-like water clusters that form within the larger nanotube
50 citations
TL;DR: This work describes a methodology for detecting solidlike NaCl clusters and following their evolution in time until they achieve nucleation (which is very rare) or dissolve back into solution, and introduces a parameter called cluster crystallinity, which is a measure of the solidlike order in a particular cluster.
Abstract: Molecular dynamics simulations are used to investigate the factors that influence the nucleation of NaCl crystals in a supersaturated aqueous solution. We describe a methodology for detecting solidlike NaCl clusters (potential nuclei) and following their evolution in time until they achieve nucleation (which is very rare) or dissolve back into solution. Through an analysis of cluster lifetimes and multiple nucleation events, we demonstrate that cluster size is not the only property that influences cluster stability and the probability of achieving nucleation. We introduce a parameter called cluster crystallinity, which is a measure of the solidlike order in a particular cluster. We show that cluster order (as measured by this parameter) has a strong influence on the lifetime and nucleation probability of clusters of equal sizes, with the lifetime and probability of nucleation increasing with increasing crystallinity. These observations remain true for clusters as small as six ions, showing that the struct...
44 citations
TL;DR: This work uses molecular dynamics simulations to investigate ice nucleation by AgI disks and plates with radii ranging from 1.15 to 2.99 nm, and shows that disks and plate in this size range are effective ice nuclei, nucleating bulk ice at temperatures as warm as 14 K below the equilibrium freezing temperature on simulation time scales.
Abstract: Silver iodide is one of the most effective ice nuclei known. We use molecular dynamics simulations to investigate ice nucleation by AgI disks and plates with radii ranging from 1.15 to 2.99 nm. It is shown that disks and plates in this size range are effective ice nuclei, nucleating bulk ice at temperatures as warm as 14 K below the equilibrium freezing temperature, on simulation time scales (up to a few hundred nanoseconds). Ice nucleated on the Ag exposed surface of AgI disks and plates. Shortly after supercooling an ice cluster forms on the AgI surface. The AgI-stabilized ice cluster fluctuates in size as time progresses, but, once formed, it is constantly present. Eventually, depending on the disk or plate size and the degree of supercooling, a cluster fluctuation achieves critical size, and ice nucleates and rapidly grows to fill the simulation cell. Larger AgI disks and plates support larger ice clusters and hence can nucleate ice at warmer temperatures. This work may be useful for understanding the mechanism of ice nucleation on nanoparticles and active sites of larger atmospheric particles.
38 citations