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Stability of Sterically Stabilized Monodisperse Fluorinated Spheres

Licentiate seminar

Den 11e december kl. 10:30 håller Kristin Jonsson sitt licentiatseminarium i KB-salen, Kemihuset, Campus Johanneberg.

Opponent: Jerome Crassous, Lund University

Handledare: Johan Bergenholtz

Examinator: Gunnar Nyman

Abstract:

Colloidal particles dispersed in a medium are important both in nature and in industry. The stability of colloidal particles is determined by the interactions between them and can be improved by steric stabilization. There is no conclusive understanding of how these sterically stabilized particles become unstable. In order to understand the loss of repulsion that leads to instability, model systems of well-defined dispersions are needed.

A semi-batch emulsion polymerization scheme has been used in this work in order to yield highly monodisperse, spherical core-shell particles in an aqueous medium. The cores of the particles are fluorinated, resulting in a refractive index close to that of water. By having the particles almost refractive index-matched, the core-core van der Waals attractions are minimized. This makes it easier to determine the role of the grafted polymers.

In order to test the versatility of the synthesis scheme, crosslinked particles and particles with a polystyrene core, instead of the fluorinated core, have been synthesized. Moreover, syntheses with different lengths of the grafted polymer, yielding different thicknesses of the particle shell, have been performed. The stability of the colloids with respect to the addition of sodium carbonate has been tested. The results show that the particles with the shortest grafts are the most stable ones. For longer grafts, the stability limit, in terms of added salt, levels out. These experimental results have been fitted to a Flory-Huggins based equation.

Date: 12/11/2017

Time: 10:30 AM - 12:00 PM

Categories: Science

Contact person: Gunnar Nyman

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