| Encapsulation is a widely used formulation tool in many areas where substances need to be delivered to a target medium while being protected from the surrounding environment until delivery conditions are reached. Some applications include drug delivery, taste and odor masking, fragrance encapsulation, and encapsulation for bio-active molecules and cells.;A novel type of microcapsules has been recently developed with great promise as a microencapsulation vehicle. This new type of capsules, known as colloidosomes, have a shell made up of individual colloidal particles as building blocks and are generated from Pickering emulsion templates. In this work, the first example for stimulus-responsive colloidosomes which completely dissolve upon a mild pH change is shown.;These particles have been applied as sole stabilizers for a double water-in-oil-in water emulsion, where the middle phase is an easily extractable oil. The double emulsion-solvent extraction approach allows the generation of colloidosomes with a higher yield and encapsulation efficiency than typical single-emulsion methods. Removal of the middle oil phase by evaporation produces water-core colloidosomes that have a shell made of pH-responsive nanoparticles, which rapidly dissolve upon a mild pH change.;The generation of colloidosomes is still, however, a complex problem where many simultaneous requirements need to be met and where many fundamental mechanisms play a role. Some of these underlying physico-chemical mechanisms are studied on passing, such as the effect of ionic strength and pH on Pickering emulsions. With the purpose of increasing the knowledge in some of these areas, important not only for colloidosome generation but also for Pickering emulsification in general, an in-depth study regarding the role of particle surface roughness on Pickering emulsion stability is also developed. This topic is selected since it is lacking controlled experimental evidence. xv ii Additionally, the pH -responsive nanoparticles synthesized and used as building blocks for the colloidosomes provided a unique opportunity to generate an experimental scheme that would allow this study in a systematic way.;Interesting results regarding the effects of surface roughness on long-term emulsion stability were obtained by emulsion centrifugation studies. These results show that surface roughness increases the emulsion stability of decane-water systems (to almost twice), but only up to a certain point, where extremely rough particles produced less stable emulsions presumably due to a Cassie-Baxter wetting regime. Additionally, in an octanol-water system, surface roughness was shown to affect the type of emulsion generated.;These results are of exceptional importance since they are the first controlled experimental evidence regarding the role of particle surface roughness on Pickering emulsification, thus clarifying some conflicting ideas that exist regarding this issue. This work significantly advances the knowledge of Pickering emulsion stability regarding particle surface roughness, and provides a new parameter in Pickering emulsification. Certainly, many more studies that deal with the wetting regimes of particles at liquid-liquid interfaces, the dynamics of wetting and emulsification and the role of surface roughness on other systems are to be expected in the future, led by the work developed here. (Abstract shortened by UMI.). |
