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Abstract

Self-assembly processes at mesoscopic length scales (approx. 10 nm–100 μm) are both of fundamental interest, due to analogies but also substantial differences to self-assembly at the molecular level, as well as of technological relevance for novel manufacturing methods with objects of such dimensions. As model systems to investigate certain aspects of this new and exciting field emerging from supramolecular chemistry, the assembly behavior of different colloidal materials onto a variety of silane layer patterns was studied. The utilized particles were either hydrophobized silica spheres or polymer latices (the plural of `latex') (composed of polystyrene, polybutylacrylate, and polybutylmethacrylate, respectively) synthesized by emulsion polymerization with various amounts of ionizable surface groups (sulfate for polystyrene, methacrylic acid for the polyacrylate and -methacrylate latices). The patterned silane monolayers were obtained by a photolithographic patterning process from trialkoxysilanes with hydrophobic (alkyl chains), polar and reactive (amino function), or charged (quaternary trimethylammonium) substituents. Both, the particles and silane patterns cover a large range from hydrophobic to hydrophilic and non-charged to highly charged systems. The colloid assembly behavior for certain particle-pattern combinations was investigated in organic and aqueous media, with a variation of pH in the latter providing precise control over the particle's preference for a specific surface type. The influence of capillary forces on the assembly process during the drying stage was also examined at different pH values. A qualitative picture of the assembly mechanism under such varying conditions is drawn from the experimental results.