Description:

Variable emissivity coatings (VEC) are advantageous for space technologies that are subject to extremely diverse thermal environments; ideally, the VEC would have a metallic phase (low emissivity) at low temperatures and an insulator phase (high emissivity) at high temperatures. There are few groups of materials that exhibit variable emissivity, such as Tungsten Oxide (WO3), Vanadium Dioxide (VO2), and perovskite oxides. Tungsten Oxide is a promising electrochromic material that can achieve a change in emissivity of 0.4. However, all electrochromic materials need an applied electric field to achieve the variance, which ultimately leads to added weight. Vanadium Dioxide has a thermochromic metal-insulator transition at ~345 K; however, the VO2 acts as an insulator at low temperatures and a metal at high temperatures which is not ideal for radiative thermal management. One promising perovskite oxide material that has a metallic phase at lower temperatures and an insulator phase at higher temperatures is Lanthanum Strontium Manganite (LSM). The change in emissivity of LSM has not been demonstrated to be >0.4. Here I propose a four task, multi-disciplinary effort to engineer micropatterned LSM-BaSO4 coatings as ultra-effective VECs, aiming to achieve a change in emissivity of >0.8. The temperature-dependent dielectric function of LSM will be predicted using ab-initio calculations, then validated experimentally with ellipsometry. The photon transport through the VEC will be modeled using Monte Carlo coupled with geometric optics to obtain the coatings reflectivity and emissivity. Machine learning and optimization methods will allow me to optimize the mesh sizes, range of particle sizes, and layer thicknesses to achieve best efficiency. The identified optimal micropatterned VEC will then be experimentally fabricated using laser-sintering and screen printing. Finally, the temperature-dependent variable emissivity and the reliability of the transition will be characterized. This proposed work is expected to achieve an ultra-effective VEC.

Benefits: This proposed work is expected to achieve an ultra-effective variable emissivity coating (VEC) to support space technologies that are subject to diverse thermal environments.