Direct Writing and Controlling of Hierarchical Functional Metal-Oxides: Bio-inspired Multiphase Processing, 3D Printing and Hierarchical Cellular Structuring

Nature-inspired processing of complex reticular/cellular architected materials by selectively incorporating multiphase materials in emulsions with targeted interactions is reported in this work. In particular, structuring of TiO 2 foams at different scales is realized by combining colloidal processing and 3D printing with fundamental understanding of the TiO 2 nanoparticle system. Specifically, hybrid TiO 2 /Ti-organic aqueous suspensions are emulsified with bio-compatible and naturally synthesized oil stabilizers where air bubbles are trapped, forming the cells of the wet foams, which are subsequently directly written as planar and three-dimensional free-standing and spanning structures. Variations in the formulation of these emulsions are implemented to tune their viscosity and render diverse cell morphologies (i.e., open- or closed-cell foam configurations) while controlling their micro-, meso- and macro-porosity. Investigation of the foams’ curing using heat versus UV light indicates differences in the emulsion’s oil-phase elimination mechanism with effects in their microstructure, which, added to the characteristic relationships between the foams’ microstructures and their photocatalytic activity, can be used to target specific properties. Our synthesis method, adjusted from the cosmetics industry, combines inorganic processing with emulsion systems of non-toxic and abundant material precursors to realize hierarchically ordered mesoporous titania foams. This method can be further exploited with other metal-oxide materials systems and even more complex emulsions to meet the needs of the currently growing technologic application fields. Moreover, we anticipate our family of foams to be readily relevant for a plethora of applications including catalysis, energy harvesting and recovery, and biomedical. Designed to be safe and water-compatible, our multi-phase emulsion systems marry high control over the materials’ microstructure and interfaces with scalable, affordable and responsible manufacturing.