A Closer Look at Colloidal Emulsions, Particles, and Supraparticles

The research in this PhD thesis focuses on colloidal particles—particles with sizes ranging from a few nanometres to micrometres. In terms of size and properties, they lie between the atomic world and the macroscopic world. They exhibit characteristics of both: their movements are strongly influenced by temperature, and like atoms, they can form crystals. At the same time, forces such as gravity can also play a role in larger colloids. This makes them ideal model systems for studying (new) materials. In this thesis, we examine both individual colloidal particles and (ordered) assemblies of these particles. These ordered structures are formed through a process called self-assembly. We start by investigating the formation of emulsion droplets with precisely controlled sizes in a microfluidic chip — an essential step for producing supraparticles, which are larger particles composed of smaller ones. The chip successfully produced monodisperse oil-in-water emulsions with droplet sizes around 1.3 μm and polydispersities as low as 6%. Experiments using various types of oils with increasing viscosity suggested a generally positive effect of the viscosity on the droplet formation. The following two chapters focus on studying colloids using confocal fluorescence microscopy. We first explore this technique through simulations of microscopy images, and then chemically synthesize colloids of various sizes to investigate how particle size affects the quality of the microscopy images. Simulations demonstrated that particle coordinates can be reliably obtained for particles with final sizes on the order of 400 nm. The experiments largely confirmed these findings, but also showed the effect of noise and the importance of matching the refractive index of the particles with that of the surrounding medium. Finally, in chapter 5, we focus on supraparticles with a specific icosahedral symmetry, which can exhibit unique optical properties, such as structural colour. Analysis revealed that the centre of symmetry in supraparticles is often off-centre, and partially crystalline structures provided insights into the self-assembly process. This thesis combines experiments and simulations of microscopy data to gain insights into colloidal self-assembly and the microscopic techniques required to study these processes.