Three-Stage Multilayer Formation Kinetics during Adsorption of an Anionic Fluorinated Surfactant onto Germanium. 1. Concentration Effect
- 14 December 2005
- journal article
- Published by American Chemical Society (ACS) in The Journal of Physical Chemistry B
- Vol. 110 (1), 295-304
- https://doi.org/10.1021/jp0549069
Abstract
The adsorption of tetraethylammonium perfluorooctylsulfonate (TEA-FOS) from aqueous solution onto hydroxylated germanium is studied using in situ polarized attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR). The adsorption is monitored at a series of bulk solution concentrations spanning from well below to above the critical micelle concentration (CMC; 1.0 mM). The kinetics of adsorption is followed by monitoring the intensity of the fluorocarbon bands. The orientation of the fluorocarbon director with respect to the germanium surface is determined by circular dichroism measurements of CF2 stretching bands. At bulk concentrations ranging from 10% of the CMC to at least 500% of the CMC, the adsorption occurs in an unusual sequence of three stages. Initially, rapid adsorption occurs within 200 min, leading to coverage of a monolayer or less. A long period of slow adsorption follows, during which we hypothesize that surfactant molecules form clusters, some of which serve as nuclei for multilayer growth. This stage concludes suddenly with an acceleration in the rate of adsorption, which eventually leads to multilayer formation. Because this is an anionic surfactant adsorbing onto a negatively charged surface at pH 6, the tetraethylammonium ions must mediate the interactions between the surfactant headgroups and the surface. The dichroism measurements show that TEA-FOS is initially oriented randomly or somewhat parallel to the surface, but over time adopts an orientation somewhat normal to the surface. This behavior is consistent with initial adsorption at isolated sites, followed by aggregation into isotropic admicelles, and finally growth into flattened admicelles. The sudden onset of accelerated adsorption can be explained either by autoaccelerating adsorption or nucleation and growth of a hydrophobic multilayer structure.Keywords
This publication has 59 references indexed in Scilit:
- Controlling Nanopore Size and Shape by Fluorosurfactant Templating of SilicaChemistry of Materials, 2005
- Formation of Tethered Nanolayers: Three Regimes of KineticsMacromolecules, 2002
- H and 19F NMR Study of the Counterion Effect on the Micellar Structures Formed by Tetraethylammonium and Lithium Perfluorooctylsulfonates. 1. Neat SystemsThe Journal of Physical Chemistry B, 1999
- H and 19F NMR Study of the Counterion Effect on the Micellar Structures Formed by Tetraethylammonium and Lithium Perfluorooctylsulfonates. 2. Mixed SystemsThe Journal of Physical Chemistry B, 1999
- Conformational and orientational order and disorder in solid polytetrafluoroethyleneMolecular Physics, 1999
- Adsorption isotherms of perfluorocarbon surfactants from aqueous and non-aqueous solutions and friction measurements of perfluorosurfactant-adsorbed aluminaColloids and Surfaces A: Physicochemical and Engineering Aspects, 1995
- Properties of fluorinated non-ionic surfactant-based systems and comparison with non-fluorinated systemsColloids and Surfaces A: Physicochemical and Engineering Aspects, 1994
- Fluorinated surfactants in bloodJournal of Fluorine Chemistry, 1994
- Atomic force microscopic characterization of a fluorinated alkanethiolate monolayer at gold and correlations to electrochemical and infrared reflection spectroscopic structural descriptionsLangmuir, 1993
- Improved capillary zone electrophoretic separation of basic proteins, using a fluorosurfactant buffer additiveJournal of Chromatography A, 1991