Heating and cooling of buildings in the United States accounts for 15 percent of energy use and 32 percent of carbon dioxide emissions. Aerogels are low-density, superinsulating nanomaterials that can dramatically reduce these numbers but are expensive to manufacture. While the insulation market is about $40 billion, aerogels account for less than 1 percent of it. Fossil-fuel-based transportation accounts for another 27 percent of emissions. Mechanically-robust aerogels can be used as lighter weight replacements for plastics to reduce the weight of vehicles, improving fuel efficiency by 10 percent. During aerogel manufacturing, supercritical carbon dioxide-based extraction is commonly utilized to remove liquid from a gel while preserving the solid nanostructure of the gel skeleton. This process accounts for as much as 50 percent of manufacturing costs, requires copious amounts of carbon dioxide and energy and stifles throughput. This research award will provide a scientific foundation to enable development and piloting of fast, efficient drying processes that preserve the skeleton of aerogels. It will enable lower costs, scaling of quantities and dimensions and diversification of materials. Porous three-dimensional nanomaterials other than aerogels are pervasive across many fields; for example, artificial tissue scaffolds. Results generated from this research will be relevant to the manufacture of such other nano-scale materials and structures. The work plan includes development of a pre-college STEM curriculum and distribution of public-friendly content about nanotechnology through an online outreach portal.
The enabling technical output is a model of mass transfer in supercritical carbon dioxide under aerogel drying conditions that captures the effects of fluid composition, compressibility and properties and, additionally, material microstructure and strain. This model will enable the determination of modulation of flow rates, temperatures and pressures, select solvents, order pore-fluid exchanges and formulate gels to develop and pilot inexpensive, fast drying processes that minimize macroscopic and nanoscopic damage to aerogels. The technical approach consists of five Tasks. (1) Measure drying kinetics as a function of process parameters to aid in model development and iteratively refine pilot-scale nanomanufacturing; (2) Measure densities of supercritical carbon dioxide-solvent systems and develop metrology to monitor drying; (3) Measure diffusion coefficients; (4) Measure volumetric strain states inside gels in situ as they are dried; and (5) Use small-angle X-ray scattering to elucidate effects of drying on and correlate stresses with morphostructural changes and identify materials for pilot testing. The fundamental nanomanufacturing principles will be applicable to a range of inorganic, polymeric and composite aerogels.
