Manufacturing a Robust Thermal Metamaterial Platform based on Carbon Nanolattices

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While the abilities to control electricity and light have led to revolutionary progress in electronics and photonics, the ability to control heat has made relatively little progress. This is mainly due to the limited understanding of thermal transport at the nanoscale and the lack of metamaterials designed to control heat transfer. The Principal Investigators (PIs) plan to manufacture carbon-based cellular materials (i.e. carbon nanolattices) and establish a new field of thermal metamaterials. The new thermal transport and manufacturing knowledge developed in this program will guide future designs of metamaterial systems and enable developments of novel thermal insulators and thermal rectifiers. The outcomes of this research will strengthen innovation in the areas of thermal control, thermal insulation, and waste heat recovery, which will enhance the energy production in the United States, so that the research directly impacts economic welfare and national security. The research outputs will be integrated with educational activities and outreach efforts.One of main challenges in studying thermal transport mechanisms or manipulating heat flows is the diffusive nature of phonon transport, which takes over when the material size is greater than the phonon mean-free-path. The PIs will utilize the measurement and processing capabilities of two synergistic labs to create a novel metamaterial platform with feature sizes smaller than the phonon mean-free-path. The first objective is to control size, geometry, and nanostructure of carbon nanolattices via a state-of-the-art two-step additive manufacturing process, consisting of two-photon polymerization direct laser writing of a polymeric template, followed by pyrolysis of the template. The process allows fabrication of structurally robust and dense polymeric lattice materials with feature sizes at the submicron range (200-1000 nm); by accurate control of the pyrolysis, the PIs will further improve the resolution, enabling fabrication of carbon structures with exquisite control of the feature size (20-200 nm). At the same time, this process allows realization of complex three-dimensional (3D) geometries that are difficult to fabricate with conventional subtractive processes, enabling an enormous design space. By simultaneously optimizing the lattice topology and the pyrolytic carbon nanostructure, the project will exploit unique size effects in thermal conductivity. The second objective is to demonstrate a new thermal metamaterial platform based on carbon nanolattices, and this project will present two target systems including a robust thermal insulator that offers a unique combination of low thermal conductivity and high mechanical strength, and a thermal rectifier that offers novel direction-dependent thermal transport properties. The project will identify thermal transport mechanisms in architected nanolattices and develop multiscale and multifunctional optimal design models that incorporate size effects and allow exploitation of asymmetric geometries. The PIs will achieve these objectives by combining their complementary expertise in thermal and mechanical sciences, microscale metrology, 3D manufacturing, and topology optimization.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.