Ice nucleation at the nanoscale probes no man’s land of water

Abstract

At a given thermodynamic condition, nucleation events occur at a frequency that scales with the volume of the system. Therefore at the nanoscale, one may expect to obtain supercooled liquids below the bulk homogeneous nucleation temperature. Here we report direct computational evidence that in supercooled water nano-droplets ice nucleation rates are strongly size dependent and at the nanoscale they are several orders of magnitude smaller than in bulk water. Using a thermodynamic model based on classical nucleation theory, we show that the Laplace pressure is partially responsible for the suppression of ice crystallization. Our simulations show that the nucleation rates found for droplets are similar to those of liquid water subject to a pressure of the order of the Laplace pressure within droplets. Our findings aid the interpretation of molecular beam experiments and support the hypothesis of surface crystallization of ice in microscopic water droplets in clouds.

Computational investigation of surface freezing in a molecular model of water

“…The model of choice for the overwhelming majority of computational studies of surface freezing has been the coarsegrained monoatomic water (mW) potential (27). Li et al (28) and Haji-Akbari et al (29) use forward-flux sampling (FFS) (30) to compute nucleation rates in droplets (28) and freestanding thin films (29) of supercooled mW. By comparing the nucleation rates in the bulk (29,31) and in confined (28,29) geometries, they both conclude that surface freezing is suppressed in the mW system.…”

“…Li et al (28) and Haji-Akbari et al (29) use forward-flux sampling (FFS) (30) to compute nucleation rates in droplets (28) and freestanding thin films (29) of supercooled mW. By comparing the nucleation rates in the bulk (29,31) and in confined (28,29) geometries, they both conclude that surface freezing is suppressed in the mW system. These findings are interesting in the sense that the mW system satisfies (32) the partial wettability condition articulated in refs.…”

Communication: Distinguishing between bulk and interface-enhanced crystallization in nanoscale films of amorphous solid water

“…[11][12][13][14][15] The idea is that when ASW is heated above its glass transition, it will transform into a supercooled liquid prior to crystallization. The crystallization kinetics will provide information about the properties of supercooled liquid water.…”

“…6,[13][14][15][43][44][45][46][47][48][49] Most experiments measure the crystallization kinetics and then extract the nucleation rate from the crystallization rate data. However, this can be complicated by the fact that crystallization of supercooled liquid water involves both nucleation and growth components.…”

“…Some studies have argued that crystallization begins at the liquid-vapor interface or free surface interface. 15,44,45 These results are explained by the higher free volume and lower density at the interface compared to the bulk which allows for the formation of larger water clusters and eventually nuclei formation. Conversely, others have reported that nucleation begins in the bulk.…”