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TY  - THES
AU  - Kleshchanok, Dzina
TI  - Polymer induced colloidal interactions : measured by direct and indirect methods
CY  - Aachen
PB  - Publikationsserver der RWTH Aachen University
M1  - RWTH-CONV-112487
SP  - 161 S. : Ill., graph. Darst.
PY  - 2007
N1  - Prüfungsjahr: 2007. - Publikationsjahr: 2008
N1  - Aachen, Techn. Hochsch., Diss., 2007
AB  - In this thesis we study interaction potentials between colloidal particles and a wall and between colloids in bulk using direct methods, such as Total Internal Reflection Microscopy (TIRM), and indirect techniques, such as Static Light Scattering (SLS). The work was motivated by the observation that the physical properties of colloidal suspensions, e.g. solution structure and phase behaviour, differ from the bulk behaviour in the ultimate vicinity of an interface. The structural properties of bulk suspensions can often be quantitatively described, knowing the pair interaction potential between the colloids. We show this for example in chapter 5 of this thesis for the case of associating colloids. It is reasonable to conjecture that the interaction of the colloidal particles with an interface is one of the reasons for the deviating behaviour of suspension as compared to the bulk. Therefore it was the task of this work to study this type of interaction potential experimentally, with the long time goal to provide input information for the treatment of near wall properties with theoretical techniques and/or computer simulation. The focus of this work is on polymer-induced interactions in colloidal systems. We have directly studied bridging attraction and steric repulsion due to attached polymer layers as well as depletion attraction due to non-adsorbing polymer chains. A detailed discussion of various other types of forces and interactions such as, van der Waals attraction, electrostatic interactions, structural forces, capillary forces, etc. is beyond the scope of this work and these forces will be mentioned here only briefly. On the basis of the experimentally obtained interaction potentials information about the colloidal near wall properties, i.e. surface phase behaviour can be obtained and compared with microscopic observations. To perform the microscopic observations in a wide range of colloidal concentrations and to avoid multiple scattering we needed particles which are easy to index-match with the solvent that was water in all our studies. Moreover, to enable a precise image analysis these colloids needed to have core-shell morphology with a fluorescent core and a non-fluorescent shell. Therefore, we introduced a new type of colloidal particles: fluorinated fluorescent latex with core-shell morphology which has a refractive index close to that of water. In the future these particles will be used to study the colloidal phase behaviour at the surface in solutions of biological depletants such as fd-viruses. This thesis begins with an introductory chapter (chapter 1) about polymer-induced forces which is intended to give the reader an overview of possible interactions in colloid-polymer mixtures. In this chapter we review some theoretical approaches and collect experimental data of polymer-induced forces, which were obtained using various techniques. Our main experimental technique, TIRM, is described in detail in chapter 2, where we also compare it with other techniques which enable direct measurements of interactions in colloidal systems. In chapters 3 and 4 we present directly measured interaction potentials between a colloidal sphere and a solid wall immersed in polymer solutions. Two different types of interactions were found depending on the nature of the polymer. Thus, in chapter 3 we show that dextran (a biopolymer) does not adsorb onto the glass and particles’ surfaces and this leads to an attractive depletion interaction. The polymer size polydispersity is shown to significantly influence the depletion potential. On the other hand, polyethylene oxide was found (chapter 4) to adsorb onto the surfaces of the colloidal sphere and the glass wall, leading to a steric repulsion between adsorbed polymer layers. In chapter 5 we present an indirect method to study interactions in colloidal systems. Thus, aqueous solutions of m-oxyethylene-n-ether (CnEm) non-ionic surfactants have been studied by static light scattering. We propose semi-phenomenological expressions for the pair interaction potential in aqueous CmEn-solutions, which enable the quantitative description of the scattering behaviour and the phase diagrams for five different surfactant systems. In chapter 6 we present a new model system to study the colloidal phase behaviour at the surface: fluorinated fluorescent latex spheres, which have a low refractive index and are highly charged and are therefore, almost transparent and very stable in water. These qualities make the particles very useful in studies with biological materials. Moreover, the morphology of these colloids, consisting of a fluorescent core and a non-fluorescent shell, makes them especially suited for studies using confocal microscopy. In future these particles will be used to directly determine many-body interaction potentials using confocal scanning microscopy.
KW  - Kolloid (SWD)
KW  - Wechselwirkung (SWD)
KW  - Polymere (SWD)
LB  - PUB:(DE-HGF)11
UR  - https://publications.rwth-aachen.de/record/49919
ER  -