How ice grows from premelting films and water droplets

Close to the triple point, the surface of ice is covered by a thin liquid layer (so-called quasi-liquid layer) which crucially impacts growth and melting rates. Experimental probes cannot observe the growth processes below this layer, and classical models of growth by vapor deposition do not account for the formation of premelting films. Here, we develop a mesoscopic model of liquid-film mediated ice growth, and identify the various resulting growth regimes. At low saturation, freezing proceeds by terrace spreading, but the motion of the buried solid is conveyed through the liquid to the outer liquid-vapor interface. At higher saturations water droplets condense, a large crater forms below, and freezing proceeds undetectably beneath the droplet. Our approach is a general framework that naturally models freezing close to three phase coexistence and provides a first principle theory of ice growth and melting which may prove useful in the geosciences.Comment: 32 pages, 10 figure

Water adsorption and desorption pretreatment of surfaces increases the maximum amount of adsorbed water molecules by a multiple

Die Menge von an einer Oberfläche adsorbiertem Wasser in einer Atmosphäre mit 100% relativer Luftfeuchtigkeit kann um ein vielfaches gesteigert werden, wenn die Oberfläche durch wiederholte Zyklen von Adsorption und Desorption von Wasser vorbehandelt wird. Dies wurde beobachtet an Oberflächen aus Diamant, Titandioxid und Siliziumdioxid bei Temperaturen um 22°C. Mit einer hinreichenden Anzahl dieser Zyklen wird eine schnellere und stärkere Adsorption von Wassermolekülen erreicht, verglichen mit unbehandelten Oberflächen. Dies bedeutet auch einen erhöhten Energieaustausch zwischen der Atmosphäre und der Oberfläche. Durch die Vorbehandlung wurde die Menge des adsorbierten Wassers um mehr als das dreifache erhöht. Der beobachtete Effekt wird erklärt durch eine kleine Menge besonders angeordneter Wassermoleküle, die nach dem Desorptionsprozeß an der Oberfläche verbleibt und die Adsorption von Wasser unterstützen. Der beobachtete Effekt kann dazu genutzt werden die Oberflächen kleiner Partikel sehr wirksam über die Gasphase zu befeuchten

Using Singlet Molecular Oxygen to Probe the Solute and Temperature Dependence of Liquid-Like Regions in/on Ice

Liquid-like regions (LLRs) are found at the surfaces and grain boundaries of ice and as inclusions within ice. These regions contain most of the solutes in ice and can be (photo)chemically active hotspots in natural snow and ice systems. If we assume all solutes partition into LLRs as a solution freezes, freezing-point depression predicts that the concentration of a solute in LLRs is higher than its concentration in the prefrozen (or melted) solution by the freeze-concentration factor (F). Here we use singlet molecular oxygen production to explore the effects of total solute concentration ([TS]) and temperature on experimentally determined values of F. For ice above its eutectic temperature, measured values of F agree well with freezing-point depression when [TS] is above ∼1 mmol/kg; at lower [TS] values, measurements of F are lower than predicted from freezing-point depression. For ice below its eutectic temperature, the influence of freezing-point depression on F is damped; the extreme case is with Na2SO4 as the solute, where F shows essentially no agreement with freezing-point depression. In contrast, for ice containing 3 mmol/kg NaCl, measured values of F agree well with freezing-point depression over a range of temperatures, including below the eutectic. Our experiments also reveal that the photon flux in LLRs increases in the presence of salts, which has implications for ice photochemistry in the lab and, perhaps, in the environment