Sepiolite nanofibers structure. From tridimensional networks to bidimensional layers

The aim of this work is to obtain tridimensional (3D) networks and bidimensional (2D) layered structures from hydrogels containing high aspect ratio sepiolite nanofibers. In this sense, it is proposed an appropriate methodology by applying an oscillating shear strain field to sepiolite hydrogels which were previously obtained by sonication. The gel stability is crucial in the final structure of the spatial arrangement. Then, the influence of sepiolite concentration and shear field on hydrogel stability is assessed by studying its rheological properties in order to determine the process window to obtain 3D or 2D final nanostructure. Three hydrogels with different concentrations (0.002; 0.02 and 0.2 g sepiolite/mL water) of high aspect ratio sepiolite were analyzed. A direct relationship among the hydrogel concentration and stability gives a tool to obtain 2D or 3D nanostructures. Hydrogels with low sepiolite concentration (0.002 and 0.02 g/mL) under shear field break, giving 2D layered structure. Meanwhile, high sepiolite concentration hydrogel (0.2 g/mL) preserves 3D networks since it does not break under the applied shear field. The comparison of final structures, before and after shear field application, was performed by analyzing the corresponding dried hydrogels by Scanning Electronic Microscopy. A versatile method was proposed to prepare 2D and 3D structures from high aspect ratio sepiolite nanofibers. It is possible to tailor the final nanofibers spatial arrangement from a combination of particle concentration and applied shear field. As a consequence, the processing window as shear field for each desired final arrangement can be assessed depending on particle concentration.