(668c) Producing Next-Generation, High-Porosity, Nanocellular Polymer Insulations by the Gas Foaming Process

We have utilized both modeling as well as experimental prototypes to demonstrate that the thermal conductivity of pore-entrapped air can be substantially reduced if pore size is reduced close to, or smaller than, the mean free path of air (~ 100 nm). Since good insulations normally contain more than 95% air, this lowering of air thermal conductivity led to superior nanopore thermal insulations. The production of super insulation by creating nanoporous structures, however, has been only marginally successful due to the cost-prohibitive, supercritical drying process.

Here we present a new method for achieving sub-micron pore structures in high-porosity foams using a gas blowing process. By substantially increasing the nuclei population through homogeneous nucleation in a gas foaming process, we expect to reduce the average pore size, within the foam, by two orders of magnitude compared to current state-of-the-art. A rigorous kinetic and thermodynamic nucleation theory is derived to verify the feasibility of such an approach. Results have shown that by reducing the dynamic interfacial tension during the bubble formation process, we are able to lower the critical radius of nucleation to much below 5 nanometers, and thus promote the creation of nanobubbles by the gas nucleation process. The concept of utilizing polymer side-chain groups as “doped” nucleation centers will be discussed along with experimental analysis of foaming experiments done in a high-pressure foaming vessel.