Schiume ed emulsioni per applicazioni a terra e nello spazio

Many of the things around us are “Soft Matter”. Soft Matter can form complex, out-of-equilibrium, and marginally stable structures that are extremely interesting from the perspective of fundamental research. Investigating their dynamic and structural properties from the molecular to the macroscopic scale, and then understating the physical mechanisms behind them, is a captivating challenge with significant implications for their exploitation in various technological fields. Multi-phase soft-matter structures where one phase is finely dispersed in another, such as in emulsions or colloidal suspensions, or where there is percolation of two or more immiscible phases, as in bijels or open-cell foams, are primarily characterized by a high surface/interface density. This characteristic makes them ideal systems for applications in synthetic chemistry, catalysis, adsorption or desorption of chemical species, drug delivery. At the same time, the low interaction energies among the constituents of soft matter structures are responsible of properties such as a mechanical response intermediate between solids and liquids, the ability to respond to external stimuli, to self-assembly or to disassembly, etc. As such, soft matter multi-phase structures are intensively studied for the creation of new materials with applications ranging from food to cosmetics and pharmaceutics, as well as in mechanical engineering and aerospace industry. This thesis is divided into two parts. The first part (sections 1-3) reports on the investigation of solid foams with photocatalytic titania nanoparticles as building blocks, designed to be the basis of high-efficiency photocatalytic oxidation filters for the degradation of contaminants in water and air, upon activation by visible light. My work started from the synthesis of doped titania anatase nanoparticles with custom thermal and optical properties; these were then conjugated with surfactant to form amphiphilic complexes that have been used as building blocks of liquid foams. The liquid foams were then stabilized into “green bodies”, i.e. organic-inorganic solid foams, that were then sintered into a purely inorganic, photocatalytic solid foam. A prototype of photocatalytic filter based on these solid foams is then proposed and tested. The second part of the thesis (sections 4-8) reports on the study of drop dynamics in marginally stable emulsions in microgravity conditions, in the framework of the project funded by the European Space Agency “Emulsion Dynamics and Droplet Interfaces - EDDI”; this research exploited the “Soft Matter Dynamics” facility onboard the International Space Station [3]. By removing sedimentation/creaming, the microgravity environment decouples and allow to study independently the different destabilization mechanisms in emulsions, such as coalescence, aggregation or Ostwald ripening. In this work, the evolution of the drop population of medium chain triglycerides (MCT) oil-in-water emulsions stabilized by non-ionic surfactant was investigated by Diffusing Wave Spectroscopy, a correlation spectroscopy technique for the study of turbid samples. Two different ageing regimes were identified: an early regime driven by coalescence between small drops, and a later regime characterized by coalescence events between small and large drops.