Counterion and Surface Density Dependence of the Adsorption Layer of Ionic Surfactants at the Vapor-Aqueous Solution Interface: A Computer Simulation Study
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- 作者：Gyö ; rgy Hantal ; Lí ; via B. Pá ; rtay ; Imre Varga ; Pá ; l Jedlovszky ; Tibor Gilá ; nyi
- 刊名：Journal of Physical Chemistry B
- 出版年：2007
- 出版时间：February 22, 2007
- 年：2007
- 卷：111
- 期：7
- 页码：1769 - 1774
- 全文大小：164K
- 年卷期：v.111,no.7(February 22, 2007)
- ISSN：1520-5207
文摘
To test the validity of currently used adsorption theories and understand the origin of the lack of their abilityof adequately describing existing surface tension measurement data, we have performed a series of moleculardynamics simulations of the adsorption layer of alkali decyl sulfate at the vapor/aqueous solution interface.The simulations have been performed with five different cations (i.e., Li+, Na+, K+, Rb+, and Cs+) at twodifferent surface concentrations (i.e., 2 
mol/m2 and 4 mol/m2). The obtained results clearly show that thethickness of the outer Helmholtz plate, a key quantity of the various adsorption theories, depends on twoparameters, that is, the size of the cations and the surface density of the anionic surfactant. Namely, withincreasing surface concentration, the electrostatic attraction between the two, oppositely charged, layers becomesstronger, leading to a considerable shrinking of the outer Helmholtz plate. Furthermore, this layer is found tobe thicker in the presence of larger cations. The former effect could be important in understanding the anomalousshape of the adsorption isotherms of alkali alkyl sulfate surfactants, while the second effect seems to beessential in explaining the cation specificity of these isotherms.
mol/m2 and 4 mol/m2). The obtained results clearly show that thethickness of the outer Helmholtz plate, a key quantity of the various adsorption theories, depends on twoparameters, that is, the size of the cations and the surface density of the anionic surfactant. Namely, withincreasing surface concentration, the electrostatic attraction between the two, oppositely charged, layers becomesstronger, leading to a considerable shrinking of the outer Helmholtz plate. Furthermore, this layer is found tobe thicker in the presence of larger cations. The former effect could be important in understanding the anomalousshape of the adsorption isotherms of alkali alkyl sulfate surfactants, while the second effect seems to beessential in explaining the cation specificity of these isotherms.