Authors Schweiß, R. ; Welzel, P. ; Werner, C. ; Knoll, W.
Title 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
Date 17.07.2001
Number 9535
Abstract 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.
Publisher Langmuir
Citation Langmuir 17 (2001) 4304-4311
Tags 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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