Capillary Bridge in Contact with Ice Particles Can Be Related to the Thin Liquid Film on Ice

Abstract

We experimentally demonstrate the presence of a capillary bridge in the contact between an ice particle and a smooth aluminum surface at a relative humidity of approximately 50% and temperatures below the melting point. We conduct the experiments in a freezer with a controlled temperature and consider the mechanical instability of the bridge upon separation of the ice particle from the aluminum surface at a constant speed. We observe that a liquid bridge forms, and this formation becomes more pronounced as the temperature approaches the melting point. We also show that the separation distance is proportional to the cube root of the volume of the bridge. We hypothesize that the volume of the liquid bridge can be used to provide a rough estimate of the thickness of the liquid layer on the ice particle since in the absence of other driving mechanisms, some of the liquid on the surface must have been pulled to the bridge area. We show that the estimated value lies within the range previously reported in the literature. With these assumptions, the estimated thickness of the liquid layer decreases from nearly 56 nm at T = −1.7°C to 0.2 nm at T = −12.7°C. The dependence can be approximated with a power law, proportional to (TM − T)−β, where β < 2.6 and TM is the melting temperature. We further observe that for a rough surface, the capillary bridge formation in the considered experimental conditions vanishes. Understanding the physics of ice and snow becomes vital as climate change accelerates. Ice exhibits exotic behavior since it is near its melting point. A liquid layer is present on ice surfaces, which is responsible for phenomena like the sticking of ice particles. Complex experiments using for example advanced laser-based methods or advanced molecular dynamics calculations have previously been used to estimate the thickness of this liquid layer. Here, we observe the formation of liquid bridges between ice and a smooth surface at temperatures well below the freezing point. We then estimate the thickness of the liquid layer on ice particles from the volume of the liquid bridge and show that it is within the range observed previously. This can help to understand this liquid layer and its relation to surface diffusion more intuitively.