Bifunctional Janus Silica Spheres for Pickering Interfacial Tandem Catalysis.

Nature provides much inspiration for the design of multistep conversion processes, with numerous reactions running simultaneously and without interference in cells, for example. A key challenge in mimicking nature's strategies is to compartmentalize incompatible reagents and catalysts, for example, for tandem catalysis. Here, we present a new strategy for antagonistic catalyst compartmentalization. The synthesis of bifunctional Janus catalyst particles carrying acid and base groups on the particle's opposite patches is reported as is their application as acid-base catalysts in oil/water emulsions. The synthesis strategy involved the use of monodisperse, hydrophobic and amine-functionalized silica particles (SiO2 -NH2 -OSi(CH3 )3 ) to prepare an oil-in-water Pickering emulsion (PE) with molten paraffin wax. After solidification, the exposed patch of the silica particles was selectively etched and refunctionalized with acid groups to yield acid-base Janus particles (Janus A-B). These materials were successfully applied in biphasic Pickering interfacial catalysis for the tandem dehydration-Knoevenagel condensation of fructose to 5-(hydroxymethyl)furfural-2-diethylmalonate (5-HMF-DEM) in a water/4-propylguaiacol PE. The results demonstrate the advantage of rapid extraction of 5-hydroxymethylfurfural (5-HMF), a prominent platform molecule prone to side product formation in acidic media. A simple strategy to tune the acid/base balance using PE with both Janus A-B and monofunctional SiO2 -NH2 -OSi(CH3 )3 base catalysts proved effective for antagonistic tandem catalysis.

Automatic Fiber Length Measurements with a Multi-Stencil Fast Marching Method on Microscopy Images.

Fiber length has a strong impact on the mechanical properties of composite materials. It is one of the most important quantitative features in characterizing microstructures for understanding the material performance. Studies conducted to determine fiber length distribution have primarily focused on sample preparation and fiber dispersion. However, the subsequent image analysis is frequently performed manually or semi-automatically, which either requires careful sample preparation or manual intervention in the image analysis and processing. In this article, an image processing and analysis method has been developed based on medial axis transformation via the multi-stencil fast marching method for fiber length measurements on acquired microscopy images. The developed method can be implemented fully automatically and without any user induced delays. This method offers high efficiency, sub-pixel accuracy, and excellent statistical representativity.