Effects of temperature on the transition from clustering to layering for argon adsorption on substrates of different strength - Parametric map of wetting, pre-wetting and non-wetting

摘要

We have carried out extensive simulations of argon adsorption on substrates of different strengths to investigate the effects of temperature on the transition from non-wetting to wetting. For moderately weak substrates, pre-wetting in the so-called "thin-to-thick film" transition occurs. We show that at a microscopic level this is a transition from an adsorbate composed of clusters to one of adsorbed layers. At the wetting temperature (T-w), this transition occurs at the saturation vapour pressure, and T-w depends on the relative strength of the intermolecular interaction between adsorbate molecules and between the adsorbate and the adsorbent, and that T-w increases as the adsorbent strength decreases. The appropriate parameter to account for the role of temperature in the wetting transition is the ratio of the isosteric heat to the heat of condensation, which is a measure of the relative strength between adsorption and cluster formation. At temperatures greater than T-w, the adsorption mechanism is layer-by-layer wetting if the wetting temperature is lower than the roughening temperature (T-R). On the other hand, if the wetting temperature is greater than T-R the mechanism is either continuous wetting or pre-wetting, which then transitions to continuous wetting when the temperature is greater than the critical pre-wetting temperature. Our study shows that the transitions from non-wetting to pre-wetting to wetting, occur not only in the first adsorbate layer, but also in higher layers.