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Authors
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Schweiß, R. ; Welzel, P. ; Werner, C. ; Knoll, W.
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Title
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Dissociation of surface functional groups and preferential adsorption of ions on self assembled monolayers in aqueous electrolyte solutions assessed by streaming potential and streaming current measurements
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Date
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17.07.2001
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Number
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9535
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Abstract
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The interfacial charge formation of self-assembled monolayers (SAMs) of thiol derivatives on gold wasinvestigated by streaming potential and streaming current measurements in aqueous electrolyte solutions.All experiments were performed at a slit channel formed by two parallel sample plates. For the first time,<IMG SRC="/images/gifchars/zeta.gif" BORDER=0 > potentials of planar SAM-solution interfaces were determined experimentally. Surface p<I>K</I> values werecalculated from the pH dependence of the <IMG SRC="/images/gifchars/zeta.gif" BORDER=0 > potential. Monolayers carrying <IMG SRC="/images/gifchars/omega.gif" BORDER=0 >-carboxylic moieties show ashift of the p<I>K</I> toward the alkaline direction as compared to the carboxy-terminated alkanethiol moleculesin solution. Contact angle titrations using a captive bubble method confirmed the dissociation behaviorof monolayers with acidic groups. Monolayers of methyl-terminated thiols exhibit <IMG SRC="/images/gifchars/zeta.gif" BORDER=0 > potential-pH plotsthat account for unsymmetrical ion adsorption. Models of the electric double layer are discussed to describethe interface between self-assembled monolayers and electrolyte solutions. Two contrary situations werefound depending on the process which generates surface charges. For methyl-functionalized SAMs, themain part of the surface charge is compensated within the diffuse double layer. In contrast, at monolayersurfaces bearin<br />g carboxylic acid groups, the main part of the countercharge was found to be located in thestagnant part of the double layer.
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Publisher
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Langmuir
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Wikidata
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Citation
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Langmuir 17 (2001) 4304-4311
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DOI
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https://doi.org/10.1021/la001741g
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Tags
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acid-base interactions atomic-force microscopy molecular films contact-angle alkanethiol monolayers polymer surfaces thiol monolayers gold surfaces titration pk(a)
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