电极/溶液界面单分子吸附层的统计力学处理 III. 汞电极上水-甲醇混合溶剂化层结构

按文11]模型, 对金属/(混合溶剂)溶液界面, 导出单分子层混合吸附等温方程并拟合计算汞/(水+甲醇)溶液界面的内层微分电容对表面电荷密度依赖关系。结果表明, 对不同组成的(H_2O+CH_3OH)混合溶剂, 计算的C_1～σ曲线与实验值甚一致。而其对应的吸附等温线则表现为在汞电极上, 由水-甲醇形成的溶剂化层几乎为甲醇分子复盖满。

Statistical Mechanical Treatment of Adsorbed Monolayer at Electrode/Solution Interface III. The Structure of Inner Layer Formed at the Interface of Hg/(H2O+CH3OH) Solution

The model proposed in previous paper was applied to metal/(mixed-solvents) solution system. According to this model, the solvation monolayer at the charged metal surface was formed by competitive adsorption of composed solvent molecules, and the dipole orientation of every solvent molecules was considered to be present in three probable states, namely, A(r)-negative end towards the metal, B(r)-positive end towards the metal, and C(r)-the dipole vector oriented at an angle Ψ(r) to the direction of electric field. Assuming the dipole orientation distribution for this adsorption layer obeys Bragg-Williams approximation and three distinctive oriented states may be converted to each other, then the mixed-adsorption isotherm could be derived by using the statistical mechanical method together with the thermodynamic equilibrium conditions.Using the equilibrium relations mentioned above and the expression for potential drop acrossed the monolayer regions, the inner-layer differential capacity (C_1) as a function of electrode charge density (σ) was estimated with curve fitting. Figure 1 shows the results of this treatment for Hg/(H_2O+CH_3OH) solution interface. In Figure 2 the corresponding mixed-adsorption isotherm curve is plotted as example, it is seen that the monolayer at Hg electrode in (H_2O+CH_3OH) solution is almost fully occupied by methanol molecules.