SNM: Low-Cost, Large-Scale Nanomanufacturing of Superinsulating Aerogels and Lightweight, Mechanically-Strong Aerogels

在美国，建筑物的供暖和制冷占能源消耗的15%，二氧化碳排放量的32%。气凝胶是一种低密度、超绝缘的纳米材料，可以大大减少这些数字，但制造成本很高。虽然绝缘材料市场规模约为400亿美元，但气凝胶只占不到1%。以化石燃料为基础的交通运输占排放量的另外27%。机械坚固的气凝胶可以用作塑料的轻质替代品，以减轻车辆的重量，提高10%的燃油效率。在气凝胶制造过程中，超临界二氧化碳萃取通常用于从凝胶中去除液体，同时保留凝胶骨架的固体纳米结构。这一过程占制造成本的50%，需要大量的二氧化碳和能源，并扼杀了产量。这项研究将为开发和试验快速、有效的干燥工艺提供科学基础，以保护气凝胶的骨架。它将降低成本，扩大数量和尺寸，使材料多样化。除气凝胶外，多孔三维纳米材料在许多领域都很普遍；例如，人工组织支架。这项研究产生的结果将与其他纳米级材料和结构的制造有关。该工作计划包括制定大学预科STEM课程，并通过一个在线推广门户网站分发对公众友好的纳米技术内容。实现技术输出是一个气凝胶干燥条件下超临界二氧化碳传质模型，该模型捕获了流体成分、可压缩性和性能的影响，此外，还捕获了材料微观结构和应变的影响。该模型将能够确定流速、温度和压力的调节，选择溶剂，安排孔隙流体交换和配制凝胶，以开发和试验廉价、快速的干燥工艺，最大限度地减少对气凝胶的宏观和纳米损害。技术方法包括五个任务。(1)测量干燥动力学作为工艺参数的函数，以帮助模型开发和迭代改进中试规模纳米制造；(2)测量超临界二氧化碳-溶剂体系的密度，发展干燥监测计量；(3)测量扩散系数；(4)原位测量凝胶干燥时的体积应变状态；(5)利用小角度x射线散射技术阐明干燥对应力的影响，并将应力与形貌变化联系起来，确定中试材料。基本的纳米制造原理将适用于一系列无机、聚合物和复合气凝胶。

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.