Mesoporous optically clear heat insulators for sustainable building envelopes.

Mesoporous materials exhibit highly controlled nanoscale structures, often templated by liquid crystalline assemblies of surfactants, with emergent and often designable physical properties. However, scaling their fabrication to be suitable for uses such as envelopes of buildings is challenging. In this work, we describe fabrication of flexible square-meter-sized films and multicentimeter-thick slabs made of three-dimensional spatial graphs of mesopore tubes that have all structural features under 50 nanometers. A solution-based kinetic fabrication process templates growing networks of cylindrical surfactant micelles with thin tubes of polysiloxane-forming gel networks and, upon replacing surfactants and solvents with air, yields lightweight materials with greater than 99% visible-range optical transparency and approximately 10 milliwatts per kelvin per meter thermal conductivity. Such predesigned metamaterials enable transparent thermal barriers for wall-grade insulated glass units, square-meter window retrofits, and unconcentrated solar thermal energy harnessing. Editor's summary: Networks of mesoporous polysiloxane tubes that are optically transparent can be used as highly thermally insulating window coatings. Bhardwaj et al. solvent-exchanged polysiloxane hydrogels with ethanol and then replaced ethanol with carbon dioxide through supercritical drying to create highly porous, graph-like networks of thin, bicontinuous tubes (see the Perspective by Li and Li). The resulting films have greater than 99% visible-range optical transparency and low thermal conductivity and can be used in new and existing windows. —Phil Szuromi [ABSTRACT FROM AUTHOR]