BM02: Multiphase Fluids for Materials Science—Droplets, Bubbles and Emulsions

Maria Torres Arango, West Virginia University

Bio-Inspired Multiphase Processing, 3D Printing and Hierarchical Structuring of Metal-Oxide Cellular Frameworks

Written by Hortense Le Ferrand

Additive manufacturing enables the layer-by-layer building up of new architectured materials. Unfortunately, the challenge usually relies in the printability of “inks” and in their rheology. Targeting photocatalytic applications, Maria Torres Arango was able to print fully inorganic foams of titanium oxide with tunable pore size and interconnectivity.

To this end, she first developed an emulsion processing mixing titanium oxide nanoparticles, a titanium organic precursor with an oily phase containing surfactants and fatty acids. After frothing, this mixture forms a foam whose bubble sizes are related to the initial composition. The viscosity of this foam can be decreased from 50 Pa.s to less than 5 Pa.s under shear and recover this viscosity after release of shear. This shear-thinning capability makes the emulsion printable and bridges up to 5 mm long that can be extruded without collapsing. To remove the organics and strengthen the liquid emulsion into an inorganic porous material, 30 minutes at 150°C are sufficient to leave macropores resulting from the bubbles, micropores from the burning of the organics, and interconnects between the nanoparticles.

Surprisingly, the structure obtained by this method offers a smaller surface area thus lesser exposure to light, yet an increased photocatalytic activity: The irradiation can reach deeper into the material.

This study exemplifies not only how colloidal science is required to tune the properties of inks to satisfy printable conditions, but also how materials research can benefit from three-dimensional (3D) printing for concrete applications.