van der Waals induced ice growth on partially melted ice nuclei in mist and fog.

Ice nucleation and formation play pivotal roles across various domains, from environmental science to food engineering. However, the exact ice formation mechanisms remain incompletely understood. This study introduces a novel ice formation process, which can be either heterogeneous or homogeneous, depending on the initial conditions. The process initiates ice crystal growth from a nucleus composed of a micron-sized partially melted ice particle. We explore the role of van der Waals (Lifshitz)-free energy and its resulting stress in the accumulation of ice at the interface with water vapor. Our analysis suggests that this process could lead to thicknesses ranging from nanometers to micrometers, depending on the size and degree of initial melting of the ice nucleus. We provide evidence for the growth of thin ice layers instead of liquid water films on a partially melted ice-vapor interface, offering some insights into mist and fog formation. We also link it to potential atmospheric and astrogeophysical applications.

Comparison of alpha and beta tin for lithium, sodium, and magnesium storage: An ab initio study including phonon contributions.

We present a comparative ab initio study of Li, Na, and Mg storage in tin, including phononic effects and phase competition between α and ß Sn. Mg doping at low concentration is found to stabilize the ß phase. On the contrary, Li and Na doping is shown to reverse the stability of the phases at room temperature: Li/Na-doped α-Sn is more stable than Li/Na-doped ß-Sn up to a temperature of around 380/400 K. This may rationalize the formation of α-Sn upon lithiation and delithiation of ß-Sn anodes reported in experimental studies. The changes in phase stability with Li/Na/Mg doping are directly related to the intercalation energies of Li/Na/Mg in one phase versus the other: at 300 K, Li/Na is easier intercalated in α-Sn (-0.37/-0.08 eV) than in ß-Sn (0.06/0.49 eV), while Mg intercalation energy is, although positive (i.e., unfavored intercalation), lower in ß-Sn (0.53 eV) than in α-Sn (0.66 eV). The temperature effect is found to affect significantly the intercalation energy, by up to 0.13 eV at 300 K. Analysis of diffusion barriers shows that Li, Na, and Mg diffusion in ß-Sn is anisotropic with migration barriers along the (001) direction (respectively, 0.01, 0.22, and 0.07 eV) significantly lower than those in α-Sn (respectively, 0.20, 0.52, and 0.40 eV).

Different pathways to anomalous stabilization of ice layers on methane hydrates.

We explore the Casimir-Lifshitz free-energy theory for surface freezing of methane gas hydrates near the freezing point of water. The theory enables us to explore different pathways, resulting in anomalous (stabilizing) ice layers on methane hydrate surfaces via energy minimization. Notably, we will contrast the gas hydrate material properties, under which thin ice films can form in water vapor, with those previously predicted to be required in the presence of liquid water. It is predicted that methane hydrates in water vapor near the freezing point of water nucleate ice films, instead of water films.