Influence of a shear flow on colloidal depletion interaction

July, Christoph

Dissertation / PhD Thesis/Book

Influence of a shear flow on colloidal depletion interaction

July, C. (Corresponding author)FZJ*

2011
Forschungszentrum Jülich GmbH Zentralbibliothek, Verlag
ISBN: 978-3-89336-791-7

Forschungszentrum Jülich GmbH Zentralbibliothek, Verlag, Schriften des Forschungszentrums Jülich. Schlüsseltechnologien / Key Technologies 41, V, 105, XVIII S. (2011) = Heinrich-Heine-Universität Düsseldorf, Diss., 2011

Please use a persistent id in citations: http://hdl.handle.net/2128/4604

Abstract: In this work colloidal depletion interactions are studied in a quiescent state and under shear flow by means of total internal reflection microscopy (TIRM). Depletion interactions are very weak, entropy driven forces [1], which arise when two or more colloidal particle species are mixed. The first theoretical studies were done by Asakura and Oosawa [2, 3]. The interest in depletion forces is driven by the fact that they are able to influence phase behaviour and self organisation of synthetic and natural colloidal systems [4]. In general, depletion forces are so small that they are difficult to measure by conventional methods such as atomic force microscopy (AFM) [5, 6] or optical tweezers [7]. TIRM is one of the most sensitive methods to probe depletion interactions in colloidal systems [8–10]. This thesis starts with an overview of the fundamental forces acting on a colloid close to a wall (chapter 2). Electrostatic interactions, gravitation, van der Waals forces, and a simple depletion theory are derived for a colloidal sphere in the vicinity of a surface. These theoretical foundations are used as models to fit experimental potentials. Chapter 3 introduces the experimental methods used in this thesis and provides an illustration of the nature of evanescent illumination. The TIRM setup is explained in detail in conjunction with the data evaluation. Sample preparation, measurements of the properties of the used samples, as well as advantages and drawbacks of the employed experimental systems are further discussed in chapter 3. Methods for characterizing samples and cleaning procedures are discussed. In chapter 4, where the results of the thesis are presented, first experiments suggest that using standard TIRM methods result in artifacts when applying a shear flow and trapping the probe particle with optical tweezers at the same time. A significant advancement of this thesis is the modification of the setup in order to remove the unwanted influence of the tweezers when shearing the sample. [...]

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