Macroporous Silica Foams Fabricated via Soft Colloid Templating

Macroporous materials with controlled pore sizes are of high scientific and technological interest, due to their low specific weight, as well as unique acoustic, thermal, or optical properties. Solid foams made of titanic, silica, or silicon, as representative materials, have been previously obtained with several hundred nanometer pore sizes, by using sacrificial templates such as spherical emulsion droplets or colloidal particles. Macroporous structures in particular are excellent candidates as photonic materials with applications in structural coloration and photonic bandgap devices. However, whereas using spherical building blocks as templates may provide tight control over pore shape and size, it results in materials with an often unfavorable local topology. Templating dry-foam or compressed-emulsion structures appear as attractive alternatives, but have not been demonstrated so far for submicron pore sizes. Herein, the use of soft, flexible microgel colloids decorated with silica nanoparticles as templates of macroporous foams is reported. These purposely synthesized core-shell colloids are assembled at ultra-high effective volume fractions by centrifuging and thermal swelling, thereby resulting in uniform disordered materials with facetted pores, mimicking dry foams. After removal of the polymer component via calcination, lightweight pure silica structures are obtained with a well-defined cellular or network topology.

Automated summary

Macroporous materials with controlled pore sizes are of high interest due to their low weight and unique properties. This study reports the use of flexible microgel colloids decorated with silica nanoparticles as templates for macroporous foams, resulting in lightweight pure silica structures with well-defined cellular or network topology.