Abstract
dc:descriptionParticle-stabilized emulsions, so called Pickering Emulsions, are known for more than a century. In such emulsions particles, mostly inorganic particles in the nm to µm range, adsorb to oil/water interfaces and stabilize emulsions by coulomb and sterical repulsion. Pickering emulsions are usually of very high stability, and a lot of energy is needed when such emulsions should be broken. Emulsions which stability depends on external stimuli have drawn much attention in recent years, as they are both of academical and industrial interest for a number of reasons. This work is about a new class of stimuli sensitive emulsions, which are stabilized by “smart” microgel particles. The particles that have been applied in this work are poly(N-isopropylacrylamide)-co-(methacrylic acid) (PNIPAM-co-MAA) microgels. Microgels are soft polymer particles which are swollen by a solvent, mostly water. Crosslinking of polymer chains restricts the swelling and avoids complete dissolution of the particle. If the solubility of the polymer in the solvent changes with temperature, the microgel made from this polymer becomes thermosensitive. In this case the thermosensitive PNIPAM is used, which turns water-insoluble above a temperature of about 32-34 °C. Incorporated in a microgel, PNIPAM expels the water from the interior of the microgel at that temperature and thus the microgel shrinks. The polymerized MAA adds a pH-sensitivity to the microgel. If a base is added to the microgel, charges are generated and the increasing osmotic pressure causes the microgel to swell further. These pH and T-sensitive particles are used for emulsion stabilization, creating stable emulsions at low temperature and high pH, while the emulsions can easily be broken at high temperature and low pH. A number of different techniques, like interfacial tension measurements, interfacial rheology and cryogenic scanning electron microscopy, have been applied in order to obtain a comprehensive picture about the origin of these effects. As is turned out, the basic concepts developed for Pickering Emulsions cannot be adapted for those emulsions. In fact, the mechanism of stabilization is mainly controlled by the visco-elastic properties of the interfacial microgel layer.
Degree
thesis:*- Grantor dc:publisher
- Publikationsserver der RWTH Aachen University
- Year dc:date
- 2009
Author and committee
dc:creator, dc:contributor.*- Author dc:creator
-
- Brugger, Bastian Matthias
- Contributors dc:contributor
-
- Richtering, Walter
Subjects
dc:subject × 10Rights
dc:rights- Statement dc:rights
-
- info:eu-repo/semantics/openAccess
- Language dc:language
- eng