Superinsulation has been one of the most challenging topics because of global concerns in sustainability and energy. However, the practical underpinning needed to design the optimal cellular structure and economically manufacture high-performance thermal insulation is still challenging due to the complication of thermal transport in the foam structure involving intermolecular, interfacial, and radiation-matter interactions. Therefore, this Ph.D. thesis developed theoretical modeling for the thermal transport in thermal insulation foams and demonstrated the influence of cellular structure and material properties on the thermal insulation property of closed-cell and reticulated open-cell foams. In particular, this research also demonstrated how an optimal foam structure and the addition of radiation-blocking carbonaceous nanoparticles effectively suppress the overall heat transfer.

The research findings demonstrated that the size of struts and cell walls in the foam structure are sensitive to the foam’s expansion and cell size. Heat conduction in the solid depends on the structural tortuosity. Conduction in the gas is substantially reduced in nanocellular foams when the mobility of gas molecules is limited due to the Knudsen effect. The radiative heat transfer depends on the opacity of each cell and the number density of cells. An optimal foam structure minimizes overall heat transfer, and a material with low thermal conductivity and high radiative absorption is preferable. This research also demonstrated the impact of carbonaceous nanoparticles in the polymer at a small content on the substantially reduced thermal radiation while minimizing the increased heat conduction. Adding such nanoparticles can further reduce the optimal thermal conductivity and increase the optimal volume expansion ratio for manufacturing high-performance insulation with less polymer. In addition, thermal transport in foams is sensitive to cellular morphology. This thesis also explained the thermal transport in nanocellular open-cell foams with excellent thermal insulation performance. Furthermore, the generation of anisotropic foams could reduce the heat transfer in the transverse direction and increases the heat transfer in the longitudinal direction, providing a unique controlled heat transfer.

The models provided an in-depth understanding of the relationship between the structure and the thermal conductivity. It provides insights into the cellular structure design and material selection for thermal insulation.