Functionalization of silica surfaces and fabrication of patchy silica particles via microcontact printing

The advances in the preparation of anisotropically functionalized particles, referred to as patchy particles, have fueled increasing interest. These particles hold great potential in the field of directed self-assembly into superordinate systems, self-propelling materials and other application fields, which necessitate directional information of the colloids. Considering this capacity, the fabrication of precisely functionalized patchy particles with a controlled composition on the surface constitutes the main motivation behind this thesis. A feasible method to fabricate patchy silicon dioxide (silica or SiO2) microspheres is demonstrated. The SiO2 microspheres were chosen as a substrate due to their chemical tolerance to solvents as well as to alkaline and acidic conditions. Various approaches of a solid-state supported microcontact printing (µCP) process are investigated to create well-defined microscale functional groups, which are applicable on SiO2 microspheres as capillary-active substrates. This thesis aims to bring novelty to the field by creating building blocks with directional information through precise localization at multiple sites of the substrate with a well-defined anisotropic geometry. Moreover, the study promises an extensive degree of freedom in engineering the surface properties of precisely functionalized patchy particles, which differentiates the hereby developed method from other anisotropic colloids fabrication techniques. The results presented in the following chapters start from the basis of the development of the solid-phase µCP technique and become more complex in each subsequent chapter with certain structures and geometries. (3-Aminopropyl)-triethoxysilane (APTES) is used as the targeted functional material to transfer on the substrates since it has the feature of acting as an anchor group and enabling the further decoration on the transferred area. The method is developed by application of the aforementioned µCP onto SiO2 microspheres to form tailor-made polymeric materials on the particle surface as a patch functionality. The challenge is followed by addressing the SiO2 particles from multiple sites. At the end, capillary-assisted µCP method is also introduced, where capillary action and wetting phenomena are deployed to achieve an anisotropic particle functionalization. This investigation is performed by using low molecular weight ink (LMWI) as well as colloidal and macromolecular ink carriers. Ultimately, all the established methods in this work serve the future development of the anisotropic particle fabrication and push the limits of the currently existing particle printing methods.