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Y Lüthi

Publications and source records attributed to Y Lüthi.

4 recordsLinked to original sources
PubMed1998

Colloidal Particles at Solid-Liquid Interfaces: Mechanisms of Desorption Kinetics.

We study the sorption of colloids on equally charged surfaces. Our focus is on the time scale from hours to weeks, where adsorption is not an irreversible process but interplays with (spontaneous) desorption. Using model calculations, we show how the desorption kinetics is influenced by readsorption, a potential barrier, a secondary potential minimum, local variation of the potential, and bond aging. In the experimental part we present results of in situ observation of the sorption kinetics of polystyrene latex particles onto a glass surface. Combining the evanescent field method with video microscopy, we were able to identify the particle arrival and departure times individually and therefrom determine the adhesion time distribution function. The nonexponentiality of this function can be explained by a gamma distribution of the potential depth at the binding sites as well as by logarithmic bond aging. Copyright 1998 Academic Press.

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PubMed1998

Colloidal Particles at Water-Glass Interface: Analyzing Videomicroscopic Data.

Direct videomicroscopic observations provide a powerful tool for investigations on the deposition of colloidal particles at liquid-solid interfaces. However, the technique is also capable of producing artefacts caused mainly by limited resolution. In the present contribution we discuss the possibilities and limitations of videomicroscopic observations, focussing thereby on an application example, namely particle deposition from flow in a parallel plate channel in the presence of a repulsive barrier. We outline algorithms for the determination of the relevant quantities, indicate the pitfalls, and provide correction formulas. Special attention is paid to the kinetics of particle release, namely to the accurate determination of the distribution of the times the particles spend adhering to the surface. In our example the kinetics of the release is found to be highly nonexponential, but an adequate fit of the measured distribution of adhesion times is obtained with a stretched exponential exp[-(betatau)nu], where nu approximately 0.5 and beta approximately 3 x 10(-5) s-1. Copyright 1998 Academic Press.

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PubMed1998

Colloidal Particles at Water-Glass Interface: Deposition Kinetics and Surface Heterogeneity.

Videomicroscopy in combination with evanescent field illumination is applied to study the sorption of colloidal particles from flow in a parallel plate channel on a glass surface. The experiments, carried out in the presence of a repulsive electrostatic barrier, reveal surprisingly complex results: The glass surface, though optically flat and well cleaned, is not homogeneous, but rather the sorption occurs at a limited number of preferred sites. Moreover, these sites are not static: new sites keep appearing at random positions on the observed surface and disappearing at a rate of kd = 1.3 x 10(-5) s-1. These findings can be understood within a simple model that takes into account slow but inevitable dissolution of the glass surface. The bulk glass contains potential adsorbers, which are continuously being exposed by the dissolution process and act as transient adsorption sites, before being washed off by the flowing buffer solution. Copyright 1998 Academic Press.

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