This EArly-concept Grant for Exploratory Research (EAGER) provides funding for conducting experiments to develop a process to create polymer foams with nanoscale cell size. It has been hypothesized that nanocellular foams (or nanofoams) may be able to achieve a natural vacuum inside cells, provided the cell size is smaller than the mean free path of gas/air molecules at standard atmospheric conditions. The proposed research will test this hypothesis by creating nanofoams that have cell diameters smaller than 70 nm, the mean-free-path for air molecules. A novel processing strategy to reduce cell size based on reduced polymer surface energy will be explored. The thermal conductivity of the nanofoams will be measured and compared to foams with microscale cells as well as solid polymer.
If successful, this research could enable the production of foams with thermal insulation values as much as double that of microcellular polymer foams. Such foams could significantly impact the construction industry by improved insulation properties or the electronics industry by enabling further miniaturization through reduced material need.
?" Polymer nanofoams are thermoplastic foams with cell size ranging from 1 to 100 nanometers. It has been hypothesized that nanofoams may be able to achieve an effective vacuum inside the cells. This hypothesis is based on Knudsen effects that occur when the cell size is similar to the mean free path of the gas or air molecules inside the cell (about 70 nanometers), due to non-operative molecular collision heat transfer mechanism. If this is true, then it might be possible to achieve foams with thermal conductivity that is significantly less than the case where cells have air. This research could pave the way for higher efficiency insulation products, saving large sums of money in heating costs for buildings on the one hand, and assist in miniaturization of devices that currently must use thick sections of foam for their insulation needs on the other. In this project we have developed novel strategies for fabricating nanofoams. The most successful and significant result is the discovery of using low-temperature saturation technique for making nanofoams. This method holds great promise as a platform technology for making nanofoams in many polymer systems. The scanning electron microscope image shown here is polycarbonate nanofoam with cell size about 40 nanometers. To the best of our knowledge this is the first time that bulk nanofoam in a thermoplastic polymer has been created with cells uniformly below 50 nm. The second significant achievement is in the understanding of heat transfer behavior in polymer nanofoams. Thermal conductivity of the polycarbonate and polyetherimide nanofoams was measured to answer the key question in the title of this project. Preliminary results of thermal conductivity measurement suggested that perhaps the nanocells do indeed behave as if there was vacuum inside them. Although we do not yet have conclusive evidence, this finding is most encouraging to continue this research. These scientific and technological advances were disseminated as a poster at the FOAMS 2013 Conference, held in Seattle in September 2013. This is a specialized technical conference focusing on foams materials and technology. The poster attracted many participants from industry and academia, especially Dow Chemical and MicroGREEN Inc., for the possible applications in the insulation and building materials industries. We plan to publish these significant findings in technical journals in the near future. The idea to create nano-scale bubbles in plastics was introduced to young students at the annual Engineering Discovery Day at the University of Washington held in April 2013. Engineering Discovery Day is open to the K-12 students in Washington State. We demonstrated the foams research and technology, using nanofoams as an example and students also obtained some hands-on experience in making the foams.
