This action focused on the preparation and characterization of Pickering-type emulsions (PEs) using functionalized micro- and nano-particles, along with their use as confined spaces that can be programmed to perform an action. PEs are emulsions stabilized by solid particles (powders) rather than traditional molecular surfactant and we postulated that using particles with specific properties could impart such properties to the emulsion itself, leading to technological applications.
To this end, we first developed a protocol based on the so-called Stöber method for the production of silicon dioxide particles, to precisely control the size of the particles, load them with fluorescent dyes allowing for their visualization and modify their surfaces with functional moieties such as fullerenes and short nucleic acid sequences.
Next, we compared discontinuous and continuous-flow approaches to the preparation of the emulsions. Comparison of these different approaches, leading to emulsions with different properties, is interesting beyond the scope of this project and could in principle be applied in different fields such as cosmetics and food, where emulsions are obiquitous. It should be mentioned that, while the use of flow-focusing microfluidic devices operated in a continuous fashion allowed to produce highly monodispersed droplets, the use of solid particles as emulsifiers put the devices under intense stress and often caused their failure on the long run.
Characterization protocols for our emulsions needed to be developed, since emulsified systems are tipically observed as a whole, but we were more interested in the behaviour of the single droplets and the fate of the emulsification agent. For example we can easily describe the physico-chemical properties of creams or foams, but the observation of the single droplets/bubbles in an emulsified system is tricky. Moreover, in this action we delved deeper into the problem, by trying to observe directly the emulsifier – micro and nanoparticles – on the surface of the droplets.
Finally, we tested one of the emulsions we developed, consisting of silicon dioxide particles decorated with [60]fullerene moieties, as a chemical reactor for the light-induced generation of singlet oxygen (a powerful, eco-friendly oxidant) and the oxidation of a model substrate. In this context, each droplet in the emulsion acts as a stand-alone chemical reactor, meaning that the oxidation can be easily scaled by de facto numbering up of the reaction vessels. This, in turn, does not change the geometry of the single reaction units – a welcome feat in a chemical process such as the one considered.
