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Effect of pH, surface charge and counter-ions on the adsorption of sodium dodecyl sulfate to the sapphire/solution interface
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Physics.
2012 (English)In: Journal of Colloid and Interface Science, ISSN 0021-9797, E-ISSN 1095-7103, Vol. 378, 152-158 p.Article in journal (Refereed) Published
Abstract [en]

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 (1) over bar 02) than the C-plane (0001), corresponding to the different points of zero charge. The largest surface excess is about 6.5 mu mol m(-2), the thickness of the adsorbed layer is about 24 angstrom 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 mu mol m(-2). The metal cation strongly influences the hydration of the adsorbed surfactant. An overall picture of 'flattened micelles' for the structure of the adsorbed layer is observed.

Place, publisher, year, edition, pages
2012. Vol. 378, 152-158 p.
Keyword [en]
Adsorption, Sodium dodecyl sulfate (SOS), Aluminum oxide, Neutron reflectivity
National Category
Physical Sciences
URN: urn:nbn:se:uu:diva-178480DOI: 10.1016/j.jcis.2012.04.026ISI: 000305165500020OAI: oai:DiVA.org:uu-178480DiVA: diva2:542495
Available from: 2012-08-01 Created: 2012-07-31 Last updated: 2012-08-01Bibliographically approved

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Rennie, Adrian R.
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