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Surface and Interfacial Forces von Butt, Hans-Jürgen (eBook)

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Surface and Interfacial Forces

A general introduction to surface and interfacial forces, perfectly combining theoretical concepts, experimental techniques and practical applications.
In this completely updated edition all the chapters have been thoroughly revised and extended to cover new developments and approaches with around 15% new content. A large part of the book is devoted to surface forces between solid surfaces in liquid media, and while a basic knowledge of colloid and interface science is helpful, it is not essential since all important concepts are explained and the theoretical concepts can be understood with an intermediate knowledge of mathematics. A number of exercises with solutions and the end-of-chapter summaries of the most important equations, facts and phenomena serve as additional tools to strengthen the acquired knowledge and allow for self-study.
The result is a readily accessible text that helps to foster an understanding of the intricacies of this highly relevant topic.

Hans-Jurgen Butt studied physics in Hamburg and Gottingen, Germany. Then he went to the Max-Planck-Institute of Biophysics in Frankfurt. After receiving his Ph.D. in 1989 he went as a post-doc to Santa Barbara, California, using the newly developed atomic force microscope. From 1990-95 he spent as a researcher back in Germany at the Max-Planck-Institute for Biophysics. In 1996 he became associate professor for physical chemistry at the University Mainz, three years later full professor at the University of Siegen. Two years later he joined the Max-Planck-Institute of Polymer Research in Mainz and became director for Experimental Physics.

Michael Kappl received his PhD thesis from the Max-Planck-Institute of Biophysics in Frankfurt and worked at the University of Mainz and Siegen. Since 2002 he is a project leader at the Max-Planck-Institute for Polymer Research in Mainz. He concentrates his research activities on Surface Forces and the Interactions of Particle Bubbles as well as Monolayer Particles.

Produktinformationen

    Format: ePUB
    Kopierschutz: AdobeDRM
    Seitenzahl: 350
    Sprache: Englisch
    ISBN: 9783527804368
    Verlag: Wiley-VCH
    Größe: 18896 kBytes
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Surface and Interfacial Forces

Chapter 2
Experimental Methods

Hans-Jürgen Butt and Michael Kappl

The direct measurement of surface forces is challenging owing to their short-ranged nature. One has therefore to combine sensitive detection of forces with precise control of distance on the subnanometer scale. A critical quantity in experiments on force versus distance relations is the distance of closest approach that is actually achieved in an experiment. Surface roughness and contaminations are serious issues when trying to establish intimate contact on the nanometer scale between two objects. In contrast to friction forces, which were already studied by Leonardo da Vinci, systematic studies of surface forces were not done before the beginning of the twentieth century. For an overview of the history of the development of devices to measure surface forces, see Refs [12, 13].

Early attempts to measure surface forces were carried out by Tomlinson in 1928. He studied adhesion forces between crossed glass fibers or glass fibers and glass spheres [14]. He introduced the advantageous interaction geometry of crossed cylinders, which avoids complications in controlling the relative orientation of the surfaces as in the case of parallel plates. In subsequent experiments, Bradley [3] measured the adhesion between quartz spheres. However, these early measurements did not include a precise determination of separation distance. A first step in that direction were the experiments by Rayleigh [15], who studied the work necessary to peel a thin glass slide from a glass plate while monitoring the separation between them by interference fringes.

Figure 2.1 Schematic of a surface forces apparatus. Two mica sheets are glued to silica half cylinders to form a crossed cylinder geometry (inset on upper left). Their surfaces are brought in close proximity by micrometer screws and a double-cantilever spring mechanism and can then be moved in and out of contact by a piezoactuator. The distance between the mica sheets is measured using optical interferometry and the force is deduced from the observed deflection of the second, much softer double-cantilever spring.

In the 1950s, Derjaguin and Abricossova of the Russian Academy of Science, Moscow, and Overbeek and Sparnaay, from the University of Utrecht, the Netherlands, tried to verify the theoretical predictions of Lifshitz on the distance dependence of van der Waals forces. Derjaguin used a specially constructed microbalance with electromagnetic feedback to measure the force between a quartz sphere and a quartz plate for distances between 100 and 1000 nm [7, 8]. Their results were in approximate agreement with the theoretical predictions for van der Waals forces by Lifshitz. Overbeek and Sparnaay [9] measured van der Waals forces between parallel glass plates by deflection of a mechanical spring while observing the distance by interferometry. Their experiments were complicated by having to keep the plates precisely parallel. They measured a 500 times larger value for the interaction energy compared to Derjaguin's results and a distance dependence of the van der Waals force that was less steep than expected in theory. Later experiments by Kitchener and Prosser, Imperial College of London [10], and by the group of Overbeek and Sparnaay [11] using a sphere-plate geometry confirmed the original findings by Derjaguin and explained the discrepancy in the early experiments by Overbeek and Sparnaay as originating from residual electrostatic charges.

A significant breakthrough in the experimental study of surface forces was the introduction of the surface forces apparatus (SFA), which will be described in the next section.

2.1 Surface Forces Apparatus

The SFA developed by Tabor and Winterton [4], and Israelachvili and Tabor [6] contains two crossed silica cylinders with a radius of curvature of roughly 1-2 cm to

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