Hollow colloidal particles by emulsion templating, from synthesis to self-assembly

Abstract

This research was focused on developing a new method to prepare hollow colloidal particles in the micrometer range, based on emulsion templating, characterization of both the templates and the resulting particles from physical and chemical viewpoint, and fabrication of materials based on such particles. We obtained a new type of hollow colloidal particles with an elastically deformable shell which allows one to assemble them into foam-like materials and ordered crystalline arrays. For the preparation of hollow particles, we used an emulsion templating technique in which monodisperse silicone oil-in-water emulsion droplets, surfactant free, were used as templates for the encapsulation with solid shells consisting of a silica/siloxane copolymer. This method opens the possibility of preparing different types of hollow particles with tunable sizes and interesting properties. We also investigated the possibility of using surfactant-stabilized emulsion droplets as templates for the encapsulation with solid shells. Both the emulsion droplets used as templates and the resulting hollow shells were investigated with a variety of techniques. The size and polydispersity of the oil droplets and the thickness of the coating were determined from Static Light Scattering. Solution 29Si NMR and solid state 29Si NMR were used to obtain information about the silicon atoms bonded to different groups present in the silicone oil emulsions and in the shell material of hollow spheres, respectively. Additionally, Energy Dispersive X-rays (EDX) was used to determine the elemental composition of the shell material. Special emphasis was put on the elastic properties of the hollow shells which were measured the by Scanning Force Microscopy (SFM) nanoindentation. We demonstrated by confocal laser scanning microscopy that the shells are permeable to small molecules and that fluorescent dye molecules can be incorporated into the shell material. The morphology of the hollow shells was investigated with Transmission Electron Microscopy (TEM). We showed that the particles' deformability makes it possible to prepare new types of regularly deformed particles, bubble-like clusters and solid microcellular foams. Additionally, the hollow particles can be incorporated as defects in crystals of silica spheres.