Some data and simple models for the silanated glass-electrolyte interface
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Some data and simple models for the silanated glass-electrolyte interface J. Lützenkirchen · C. Richter · F. Brandenstein
Received: 15 March 2010 / Accepted: 20 May 2010 / Published online: 1 July 2010 © Springer Science+Business Media, LLC 2010
Abstract The interface between silanated glass and aqueous KCl electrolyte solutions was studied by zeta-potential and contact angle measurements. Variation of the pH in the zeta-potential measurements yielded a sharp isoelectric point (IEP) at about pH 4, which was independent of the KCl concentration. This particular pH corresponds to zero electrokinetic potential for many hydrophobic surfaces encompassing Teflon, polyethylene and others. The results are interpreted in terms of hydroxide adsorption at the silanated glass-aqueous interface. A previously developed model for such inert surface—electrolyte interfaces is applied to the experimental data. The model parameters are within the range of those previously obtained for comparable surfaces. Discrepancies were observed in pH dependent contact angle measurements, which were done using both the plate
Dedicated to the memory of Professor Andrzej Waksmundzki (1910–1998) on the occasion of the celebration of his 100th birthday. J. Lützenkirchen () Institut for Nuclear Waste Disposal (INE), Karlsruhe Institute of Technology (KIT), Campus Nord, P.O. Box 3640, 76021 Karlsruhe, Germany e-mail: [email protected] C. Richter Fachbereich Physik, Technische Universität Kaiserslautern, Erwin-Schrödinger-Str. 56, 67663 Kaiserslautern, Germany Present address: C. Richter Institut für Organische Chemie, Karlsruhe Institute of Technology (KIT), Campus Süd, Fritz-Haber-Weg 6, 76131 Karlsruhe, Germany F. Brandenstein Thermo Fisher Scientific, Material-Characterization-Products, Process Instruments, Dieselstraße 4, 76227 Karlsruhe, Germany
and the drop method: advancing contact angles were always higher than receding contact angles. Advancing contact angles using the drop method yielded no clear tendency as a function of pH and lower values than those obtained by the plate-method. Overall the contact angle data are presented but deemed difficult to interpret in terms of pH dependence and relation to zeta-potentials. A preliminary description of the contact angle data is attempted via the Lippman-Young equation for the different contact angle data sets based on the model potentials. The model results are discussed. Zeta-potential measurements were also performed as a function of salt content within a narrow pH range. As would be expected the presence of a 2:1 electrolyte (BaCl2 ) results in lower absolute values when compared to the KCl case. Keywords Hydrophobicity · Contact angle · Zeta-potential · Hydroxide ion adsorption
1 Introduction Studies by Andrzej Waksmundzki involved preparation and characterisation of hydrophobic surfaces (Rayss et al. 1983). Thus silanization (Dawidowicz et al. 1977) as well as zetapotential measurements on such hydrophobic surfaces (Chibowski and Waksmundzki 1978) were reported more than 30 ye
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