Abstract

We carried out a comprehensive molecular simulation to investigate the evolution of the excess isotherms and the isosteric heat with respect to temperature for argon adsorption on strong and weak substrates. The temperature ranges from well below the bulk triple point temperature to above the bulk critical temperature to show the first- (second-) order transitions and the state of the system at the bulk coexistence pressure P₀, whether it is non-wetting, partial wetting or complete wetting (preceded by pre-wetting). It is found that the key parameter that affects the dependence of the transitions on temperature and the state of the system at P₀ is the relative difference between the isosteric heat and the heat of sublimation (or condensation). For strong substrates, the state of the system changes from partial wetting to complete wetting when the temperature crosses the bulk triple point temperature, and for temperatures well below the bulk triple point the 2D-condensation occurs in the first and second (and possible higher) layers. For weak substrates, the state of the system changes from non-wetting to complete wetting when the temperature crosses the wetting temperature T_W, which is specific to the substrate. For temperatures greater than T_W, complete wetting in weak substrates only occurs at pressures close to the bulk coexistence pressure P₀ via the initial stage of clustering (unfavourable adsorption), followed by a pre-wetting (known as thin-to-thick transition), and this is reflected in the increase of the isosteric heat from a value less than the heat of condensation λ and approaching λ as the pressure tends to P₀.

Graphic abstract

中文翻译：

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吸附等温线和等排热从三重点到超临界点的演变

摘要

我们进行了全面的分子模拟，以研究过量等温线的变化以及等温线相对于温度的变化，以了解氩气在强弱基质上的吸附情况。温度范围从远低于本体的三点温度到本体的临界温度以上，以显示一阶（二阶）转变和在本体共存压力P ₀下系统的状态，无论它是非润湿的，局部的。润湿或完全润湿（先进行预润湿）。发现在P ₀处影响转变对温度和系统状态的依赖性的关键参数是等规热与升华（或凝结）热之间的相对差。对于坚固的基材，当温度超过整体三点温度时，系统状态会从部分润湿变为完全润湿；对于温度远低于整体三点的温度，二维冷凝会在第一和第二个（可能更高）发生层。对于较弱的基材，当温度超过基材特有的润湿温度T _W时，系统状态从非润湿变为完全润湿。对于高于T _W的温度，仅在接近本体共存压力P _0的压力下，才在弱基底中完全润湿。通过聚集的初始阶段（不利的吸附），然后进行预润湿（称为稀薄转变），这反映了等排热的增加，其值小于冷凝热λ和随着压力趋于P ₀接近λ 。

图形摘要