Self-assembly (SA) refers to the process by which particles or other discrete components spontaneously organize due to direct specific interactions and/or indirectly, through their environment. Structuring matter by SA with nanoparticles (NPs) has progressed significantly over the last decades, which has been driven from a materials perspective, by both improvements in the synthesis of building blocks as well as the realization of novel collective and synergistic properties induced by formed superstructures. One promising way of making functional materials is assembling building blocks into supraparticles (SPs), particles composed of particles. One of the advantages of creating SPs through the drying of emulsion droplets method, instead of methods based on the introduction of attractions through, e.g., solvophobic effect, is that it does not depend on the detailed surface chemistry of the building blocks and thus can be applied to a wider range of systems such as particle mixtures and particles with more complex shapes.
In this thesis, our focus is not yet on properties and applications of the SPs, but instead on how the spherical confinement influences the SA of NPs. In Chapter 2, by integrating experiments and computer simulations, we demonstrate that the orientational correlations of cubic NPs inside drying emulsion droplets are significantly determined by their flat faces.
In Chapter 3, we study the structures of SPs composed of nanoplatelets assembled from slowly drying emulsion droplets. We found that the spherical confinement had (almost) no symmetry altering effects on the SA as compared to bulk.
In Chapter 4, we investigate the structure and defects of SPs assembled from a mixture of binary CdSe/PbSe NPs with a size ratio of 0.76 from slowly drying emulsion droplets quantitatively. We show that binary MgZn2-Laves crystal structure is hardly influenced by spherical confinement when the experimental binary species have a slight off-stoichiometry and, moreover, contains the expected stacking faults for a bulk crystal. As a comparison, if the stoichiometry is more closely matches that of a Laves crystal, the binary NPs were found to assemble into binary SPs with an icosahedral quasicrystal structure, which are interesting for photonic application.
In Chapter 5, we demonstrate how SPs can be self-assembled by slowly drying oil dispersion droplets in water containing two kind of NPs (sphere/spheres, spheres/platelets) and how this can result in either a homogeneous, core-shell or Janus-type of morphology.
In Chapter 6, we perform the first cation exchange on SPs composed of tetrahedral CdSe NPs. By tuning the reaction time and cation solution concentration, SPs with tunable core-shell morphology can be obtained