Effect of pH, surface charge and counter-ions on the adsorption of sodium dodecyl sulfate to the sapphire/solution interface

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• 作者：Ningning Li^a ; Robert K. Thomas^a ; ^{robert.thomas@chem.ox.ac.uk} ; Adrian R. Rennie^b ; ^{Adrian.Rennie@fysik.uu.se}
• 关键词：Adsorption ; Sodium dodecyl sulfate (SDS) ; Aluminum oxide ; Neutron reflectivity
• 刊名：Journal of Colloid and Interface Science
• 出版年：2012
• 期刊代码：125_00219797
• 类别：ch
• 出版时间：15 July, 2012
• 卷：378
• 期：1
• 页码：152-158
• 文件大小：1219 K

摘要

The role of ionic interactions between sodium dodecyl sulfate, SDS, and sapphire surfaces have been studied using specular neutron reflection to determine the structure and composition of adsorbed surfactant layers. Increasing the pH of the solution from 3 to 9 reduces the adsorption by reversing the charge of the alumina. This occurs at lower pH for the R-plane (1  0 2) than the C-plane (0 0 0 1), corresponding to the different points of zero charge. The largest surface excess is about 6.5 渭mol m^鈭?, the thickness of the adsorbed layer is about 24 脜 and it contains roughly 20%water. The hydrocarbon tails of the surfactant molecules clearly interpenetrate rather than form an ordered bilayer. The structure is similar in either pure water or in 0.1 M NaCl when the surfactant is at the respective critical micelle concentration. Different structures were seen with lithium and cesium dodecyl sulfate. The CsDS forms dense layers with little or no hydration and a surface excess of about 10.5 渭mol m^鈭?. The metal cation strongly influences the hydration of the adsorbed surfactant. An overall picture of 鈥榝lattened micelles鈥?for the structure of the adsorbed layer is observed.