Ice and water droplets on graphite: A comparison of quantum and classical simulations

Nanoscale Correlations of Ice Adhesion Strength and Water Contact Angle

Surfaces with low ice adhesion represent a promising strategy to achieve passive anti-icing performance. However, as a successful and robust low ice adhesion surface must be tested under realistic conditions at low temperatures and for several types of ice, the initial screening of potential low ice adhesion surfaces requires large resources. A theoretical relation between ice adhesion and water wettability in the form of water contact angle exists, but there is disagreement on whether this relation holds for experiments. In this study, we utilised molecular dynamics simulations to examine the fundamental relations between ice adhesion and water contact angle on an ideal graphene surface. The results show a significant correlation according to the theoretic predictions, indicating that the theoretical relation holds for the ice and water when discarding surface material deformations and other experimental factors. The reproduction of the thermodynamic theory at the nanoscale is important due to the gap between experimental observations and theoretical models. The results in this study represent a step forward towards understanding the fundamental mechanisms of water–solid and ice–solid interactions, and the relationship between them.

Singular sublimation of ice and snow crystals

The evaporation (sublimation) of ice and snow has a major impact on global climate, since the amount of ice and snow determines Earth’s albedo. Yet, due to their complex geometry with several sharp regions which are singular for the evaporation, the precise evaporation dynamics of snow and ice crystals remains challenging to predict. Here, we study the sublimation of snowflakes and pointy ice drops. We show that the evaporation rates of water and ice drops are similar; they are both limited by the diffusive transport of the vapour. This allows us to predict ice and snowflake evaporation quantitatively by solving the diffusive free-boundary problem, which correctly predicts the rapid self-similar evolution of sharp edges and points. Beyond providing a conceptual picture to understand the sublimation of ice crystals, our results are more generally applicable to other diffusion problems such as the dissolution of salt crystals or pharmaceuticals.

Ice sublimation is a common, yet little-studied, heat and mass transfer problem with climatic and industrial implications. Here, the authors show that the sublimation of ice crystals is purely diffusive and is unaffected by the underlying crystalline lattice.

Water nanodroplet on a graphene surface-a new old system

The major subject of our study is the accuracy of contact angle calculations. Reporting new simulation data for graphene-water systems, we show that the majority of previously reported data should be treated with caution, since the proper contact angle can be recorded only after a sufficiently long simulation time. It has been proven that-if one wants to gain accuracy greater than 0.1°-long calculations (exceeding 50 ns) are required. Finally, we also show, using both a Groningen Machine for Chemical Simulations (GROMACS) package and our new molecular dynamics (MD) code, that the changes in the contact angle, caused by graphene bottom layer rotation, are within the range of calculation error. We also propose a novel definition of the bottom of the droplet as the height where the density is half the density of liquid water. This new definition is applied in the method of the contact angle calculation from the MD simulation data.

Three-phase contact line and line tension of electrolyte solutions in contact with charged substrates

The three-phase contact line formed by the intersection of a liquid-vapor interface of an electrolyte solution with a charged planar substrate is studied in terms of classical density functional theory applied to a lattice model. The influence of the substrate charge density and of the ionic strength of the solution on the intrinsic structure of the three-phase contact line and on the corresponding line tension is analyzed. We find a negative line tension for all values of the surface charge density and of the ionic strength considered. The strength of the line tension decreases upon decreasing the contact angle via varying either the temperature or the substrate charge density.