A generalized scale of free energy of excess adsorption of solute and absolute composition of the interfacial phase
A generalized scale of free energy of excess adsorption of solute and absolute composition of the interfacial phase
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DOI：
10.1021/la030299
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发表时间：
2004-06-08
期刊：
影响因子：
3.9
通讯作者：
Mitra, A
中科院分区：
文献类型：
--
作者：
Chattoraj, DK;Imae, T;Mitra, A
根据吸附前后本体相中溶质摩尔浓度的差异分析估计每单位面积固-液界面吸收的表面活性剂的摩尔数 (Gamma(2)(1))，与形成与均匀组成的本体相接触的不均匀表面相的溶剂和溶质的绝对组成 Delta(1) 和 Delta(2) 定量相关。通过使用等压实验，以相同的方式计算了固液界面上无机盐吸附的伽玛（2）（1）负值。根据 Gamma(2)(1) 与溶质和溶剂的体积摩尔分数之比的线性图，已在有限的浓度范围内评估了 Delta(1) 和 Delta(2) 的值。对于表面活性剂和无机盐分别在流体界面上的吸附，使用吉布斯吸附方程从表面张力浓度数据评估了 Gamma(2)(1) 值。基于流体界面附近吉布斯分割面任意放置的 Gamma(2)(1) 与不均匀表面相的组成定量相关。此外，多分量解的吉布斯方程已用适当导出的系数 m 适当地表达。对多组分体系的吉布斯吸附方程进行积分，计算了由于本体中表面活性剂的活性 α(2) 从零到 1 的变化而导致表面活性剂在流体界面处的最大吸附 Gamma(2)(m) 所导致的每单位表面积的标准自由能变化 DeltaG 度。采用类似的程序，使用热力学导出方程计算固-液界面表面活性剂吸附的 DeltaG 度。发现所有此类系统的表面活性剂吸附的 DeltaG 度值都是负值。盐在流体和固-液界面上的负吸附的 DeltaG 度的一般表达式也已根据热力学原理推导出来。由于无机盐存在下界面相过度自发水合，所有此类系统的 DeltaG 度均为正值。根据吸附自由能的广义尺度，分别讨论了过量表面活性剂和盐吸附的 DeltaG 度的负值和正值。
Moles of a surfactant (Gamma(2)(1)) absorbed per unit area of the solid-liquid interface estimated analytically from the difference of the solute molality in the bulk phase before and after adsorption have been quantitatively related to the absolute compositions Deltan(1) and Deltan(2) of the solvent and solute forming the inhomogeneous surface phase in contact with the bulk phase of homogeneous composition. By use of isopiestic experiments, negative values of Gamma(2)(1) for the adsorption of inorganic salts onto a solid-liquid interface have been calculated in the same manner. From the linear plot of Gamma(2)(1) versus the ratio of the bulk mole fractions of the solute and solvent, values of Deltan(1) and Deltan(2) have been evaluated under a limited range of concentrations. For the adsorption of the surfactant and the inorganic salt respectively onto the fluid interface, Gamma(2)(1) values have been evaluated from the surface tension concentration data using the Gibbs adsorption equation. Gamma(2)(1) based on the arbitrary placement of the Gibbs dividing plane near the fluid interface is quantitatively related to the composition of the inhomogeneous surface phase. Also, the Gibbs equation for multicomponent solutions has been appropriately expressed in terms of a suitably derived coefficient m. Integrating the Gibbs adsorption equation for a multicomponent system, the standard free energy change, DeltaGdegrees, per unit of surface area as a result of the maximum adsorption Gamma(2)(m) of the surfactant at fluid interfaces due to the change of the activity alpha(2) of the surfactant in the bulk from zero to unity have been calculated. A similar procedure has been followed for the calculation of DeltaGdegrees for the surfactant adsorption at solid-liquid interfaces using thermodynamically derived equations. DeltaGdegrees values for surfactant adsorption for all such systems are found to be negative. General expressions of DeltaGdegrees for negative adsorption of the salt on fluid and solid-liquid interfaces respectively have also been derived on thermodynamic grounds. DeltaGdegrees for all such systems are positive due to the excess spontaneous hydration of the interfacial phase in the presence of inorganic salt. Negative and positive values of DeltaGdegrees for excess surfactant and salt adsorption respectively have been discussed in light of a generalized scale of free energy of adsorption.