Understanding the Effect of Nanoparticle Size on Thermal Conductivity in Amorphous Nanoporous Materials Made from Colloidal Building Blocks

In this work, we examined the effect of nanoparticle size on the thermal conductivity of mesoporous silica materials made from colloidal precursors. Porous thin films were synthesized using a polymer-templating method, employing commercial colloidal silica solutions containing nanoparticles 6, 9, and 22 nm in diameter as the silica source and poly(methyl methacrylate) colloids as the template. The ratio of polymer to silica was then varied to produce films with a range of porosities. The thermal conductivity of the films was measured using time domain thermal reflectance, and the results indicated that, for the particle sizes studied, there was a weak dependence of thermal conductivity on particle size. This weak dependence was associated with increased interfacial scattering of heat carriers at the boundaries of the smaller nanoparticles. This work adds to our understanding of the effect of nanostructuring on heat transport in amorphous material systems and improves our ability to design low thermal conductivity materials.