A universal, template-free approach to porous oxide and polymer film processing

Abstract

We have developed a unique, template-free method for the processing of porous oxide and polymer films with a high degree of ordered porosity, taking advantage of micro-detonation. When mixing an alcoholic solution of ammonium or silver nitrate with an alcoxide precursor solution, a phenomenon of self-organization of immiscible organic solvent (Fuel)–nitrate(oxidant) micro-droplets occurs during film formation. Thermal activation leads to self-ignition reactions of the droplets resulting in the exothermic formation of gas species that upon expansion leave a porous structure behind. We demonstrate the method on thin TiO₂ films and show that hierarchical porosity may be obtained by increasing the film thickness. In order to prove the universality of the method we apply it to a polymer solution, and achieve a nicely ordered hierarchical porosity in a 20 μm thick polymer film.