Tailor-Making Nano Insulation Materials with Lowered Thermal Conductivity by Utilizing the Knudsen Effect

Abstract

As the world is turning its focus even more towards aspects like energy efficiency and renewable and non-polluting energy harvesting, including the building sector, the quest has been set for developing high-performance thermal insulation materials with very low thermal conductivities. A possible and promising pathway to achieve these thermal super insulation materials (SIM) is to utilize the Knudsen effect where the pore diameters of these materials are attempted lowered below the mean free path of the air molecules, i.e. in the nanorange, thus creating a nano insulation material (NIM) with a nanoporous structure. A particular pathway to manufacture a NIM is to make hollow silica nanospheres (HSNS) by a sacrificial template method, where one may tailor-make the HSNS by controlling their inner sphere diameter and shell thickness. Hence, one may then in principle also be able to tailor-make HSNS with the desired thermal conductivity, normally with as low thermal conductivity as possible. This study will present our latest experimental results with these NIMs made through HSNS, demonstrating a decreasing thermal conductivity with a decreasing inner sphere diameter. These experimental results are also compared with theoretical predictions by the Knudsen effect.