Coffee ring patterns of functionalized metallic or metal oxide nanoparticles on specific surfaces are the basis of technological applications such as the manufacture of transparent conductive coatings, sensors, photonic devices and microarrays used in combinatorial chemistry studies in genomics. In this manuscript it is shown that amphiphilic silsesquioxanes could be also self-assembled into coffee ring patterns on the surface of carbon films, a fact that can extend the applications of these patterns due to the versatility of the silsesquioxane chemistry. A precursor based on the reaction of (3-isocyanatopropyl) triethoxysilane (IPTES) with dodecylamine (DA) was hydrolyzed and slowly condensed in a tetrahydrofuran solution, in the presence of formic acid. The resulting colloidal dispersion of silsesquioxane nanoparticles was diluted with methanol and dip-coated on thin carbon films used as covers of TEM grids. A coffee ring pattern was spontaneously formed on the carbon surface by a combination of dewetting of the liquid film and induced capillary flow towards the pinning line. Silsesquioxane nanoparticles present in the boundary of each ring were composed of an agglomeration of crystalline nanorods (lengths of about 50-100 nm and diameters of 8 nm, as observed by HRTEM), interconnected by amorphous regions. SAED (selected area electron diffraction) showed that the inorganic Si-O-Si skeleton was organized as crystalline sheets exhibiting a 2D-hexagonal array. SAXS showed a tail-to-tail association of organic branches composed of strongly H-bonded urea groups and extended dodecyl chains  (FTIR). A scheme describing the structure of the nanorods is proposed.

Coffee ring patterns of nanostructured amphiphilic silsesquioxanes on carbon films

243rd National Meeting (2012)

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