Acharid Abdelhaq, Sadiki Mustapha, Elmanfe Galal, Derkaoui Nawal, Olier René, Privat Mireille
Département de Chimie, UMR CNRS 6521, Université de Bretagne Occidentale, 6 Av. Le Gorgeu, C.S. 93837, 29238 Brest Cedex 3, France.
Langmuir. 2006 Oct 10;22(21):8790-9. doi: 10.1021/la061160c.
This paper reports on investigations about the adsorption at the air-water surface, and for the sake of comparison at the silica-solution interface, of two 1-2 electrolytes, Pb(NO(3))(2) and PbCl(2), at first alone and then from a mixture with carbofuran or with benzene; all of them were at concentrations below 10(-2) M. The limited domain, where the Debye and Hückel formalism for solutions and the Wagner-Onsager-Samaras (WOS) model for surfaces are correct, is then respected. This study was aimed at trying to identify the part played in the surface by the different particles of the system components and in particular the role of water. When aqueous solutions of nonorganic salts are dilute enough, their surface tensions are known to be salt concentration-independent; however, the zero value of the resulting relative adsorption has never been the subject of analysis about water behavior. By combining experimental relative adsorptions and Gibbs excesses calculated from the WOS theory, we will show that, in well-known solutions such as KCl ones, where the negative excess in salt can be very precisely modeled by the WOS theory, the resulting water excess Gamma(W) is negative. The same result can be obtained by taking into account the Ray-Jones effect. This observation drove us to wonder about the results of a similar analysis done on solutions of unsymmetrical electrolytes and on mixtures of salt and organic molecules. Experiments showed that, for all of the systems, Gamma(W) was negative. For a given salt, Gamma(W) was more negative in the presence of organic molecules, and carbofuran was a more efficient water repellent than benzene; water repulsion was greater with nitrates than with chlorides. From these data, it seems that water was repelled toward the solution bulk, whereas ions probably took place between the bulk and a layer of organic molecules. These observations called for a more detailed modeling.
本文报道了关于两种1-2价电解质Pb(NO₃)₂和PbCl₂在气-水表面以及为作比较在二氧化硅-溶液界面的吸附研究，起初是单独吸附，然后是从与呋喃丹或苯的混合物中的吸附；所有这些物质的浓度均低于10⁻² M。在此过程中遵循了德拜-休克尔溶液理论和瓦格纳-翁萨格-萨马拉斯（WOS）表面模型适用的有限范围。本研究旨在确定系统组分的不同粒子在表面所起的作用，尤其是水的作用。当无机盐的水溶液足够稀时，已知其表面张力与盐浓度无关；然而，由此产生的相对吸附的零值从未成为关于水行为分析的主题。通过结合实验相对吸附量和根据WOS理论计算的吉布斯超额量，我们将表明，在诸如KCl溶液这样的知名溶液中，盐的负超额量可以由WOS理论非常精确地模拟，由此产生的水超额量Γ(W)为负。考虑到瑞-琼斯效应也可得到相同结果。这一观察结果促使我们思考对不对称电解质溶液以及盐与有机分子混合物进行类似分析的结果。实验表明，对于所有系统，Γ(W)均为负。对于给定的盐，在存在有机分子时Γ(W)更负，并且呋喃丹比苯是更有效的拒水剂；硝酸盐的拒水作用比氯化物更强。从这些数据来看，似乎水被排斥到溶液主体中，而离子可能存在于主体和有机分子层之间。这些观察结果需要更详细的建模。
