Abstract:

To explore the cluster distribution and evolution during the process of adsorption at solid-vapor interface, a series of experimental measurements and theoretical analysis are hybrid to study the characteristics of water vapor adsorption on silica and graphite surfaces. The adsorption isotherms in the full pressure range are obtained based on the Zeta adsorption model, the cluster distributions at different pressure ratios are obtained, the critical conditions for the adsorption phase change and wetting are determined. The results showed that Zeta adsorption isotherm has no singularity at saturation pressure. The adsorption measurements are in good agreement with the theoretical prediction by Zeta adsorption model. Meanwhile, the vapor adsorbate is formed as clusters with different number of molecules. In the low pressure ratio zone, small molecular clusters and zero adsorption units dominate the adsorption site. As the pressure ratio increases, the types of adsorption clusters increase. Once the pressure exceeds a certain value, the entropy reaches a maximum value, indicating the occurrence of phase transition at the interface. The surface tension of graphite and silica and the critical conditions of interfacial wetting under the condition of zero adsorption are determined. Under the wetting pressure ratio, homogeneous macromolecular clusters gather to form a liquid-film-like wetting interface.

Key words: solid-vapor interface, adsorption phase change, cluster distribution, entropy, surface tension

摘要：

为了深入探讨气固界面吸附过程中团簇分布及其演化规律，结合实验测量和理论分析研究了水蒸气在二氧化硅和石墨表面的吸附特征，获取了不同压比下的团簇分布，确定了吸附相变及润湿转变的临界条件。结果表明，实验测量结果和Zeta吸附理论预测吸附曲线吻合很好，明确了气体分子以团簇形式吸附在固体表面，在低压比区，小分子团簇和零吸附单元占主导地位，随着压比的增加，吸附团簇类型增多，当压比达到某一临界值时，吸附熵达到极大值，界面发生吸附相变。确定了零吸附情况下石墨和二氧化硅表面张力及界面润湿临界条件，润湿压比下，性质均一的大分子团簇聚集，形成类液膜润湿界面。

关键词: 气固界面, 吸附相变, 团簇分布, 吸附熵, 界面张力