Researchers have engineered a new material that is an extreme thermal insulator, is exceptionally stiff, and can be printed as a thin film at large scales. The material has one of the lowest thermal conductivity profiles of any dense, or non-porous, material - approaching the theoretical limit of how good a material can be as a thermal insulator.
"Stiff materials that are good thermal insulators would have substantial utility in a variety of applications, from cookware to electronic devices to space travel," says Dali Sun, co-corresponding author of a journal article on the work and a professor of physics at North Carolina State University.
"But this is a significant challenge," Sun says. "Because, in general, stiff materials are good at conducting heat, and materials that are not stiff are good at insulating against heat. We've created a material that is very stiff and is extremely good at insulating against heat. Better than any material you would find in nature."
"We had previously demonstrated unusual behavior related to the combination of stiffness and thermal conductivity in a specific class of materials," says Jun Liu, co-corresponding author and an associate professor of mechanical and aerospace engineering at NC State. "For this work, we engaged in more advanced molecular engineering to intentionally create an extreme combination of those properties."
The researchers worked with a subset of the class of materials called two-dimensional hybrid organic-inorganic perovskites. These are thin film semiconductors consisting of alternating organic and inorganic layers with a highly-ordered crystalline structure. By replacing some of the carbon-carbon chains in the organic layers with a tailored combination of benzene rings, the researchers can control the stiffness and thermal conductivity of the materials.
Specifically, the researchers made an azobenzene ethyl ammonium lead iodine thin film. When the researchers tested it, they found that the material had a thermal conductivity of approximately 0.04 W m-1 K-1 at room temperature. To put that in context, this stiff material has a thermal conductivity that is five times lower than silicone - which has a thermal conductivity of 0.2 W m-1 K-1. And silicone is used to insulate against heat in applications such as oven mitts.
"So, if we want to compare this material to silicone, the material we made is 700-10,000 times stiffer than silicone and five times better at insulating against heat," says Liu.
"And the method we used to produce this material can be scaled up fairly easily," says Liu. "You can produce it at fairly large scales, apply it as a coating, and so on.
"We're exciting about this material because of its properties," Liu says. "But we're also excited because this work highlights the potential of molecular engineering to fine-tune these hybrid layered materials for use in applications that require novel combinations of stiffness and thermal insulation."
The paper, "Extremely Low Thermal Conductivity in Rigid Layered Hybrid Perovskites," is published in the open-access journal Science Advances. Co-lead authors are Ziqi Wang and Ankit Negi, Ph.D. graduates of NC State; Liang Yan of the University of North Carolina at Chapel Hill; and Qingxuan Wang of Nanjing Normal University. Co-corresponding authors are Liu and Sun; Wei You of UNC Chapel Hill; and Jun Zhou of NNU. The paper was co-authored by Zarif Ahmad Razin Bhuiyan, Andrew Comstock, Subhrangsu Mukherjee, Cong Yang, Aryan Jouneghaninaseri, Shehzad Khan, Saqlain Raza, Yoji Nabei and Harald Ade at NC State; Xiaowei Zhong and Jun Hu at UNC Chapel Hill; Yeonju Yu and Qing Tu at Texas A&M University; Tyler Wang and Mengxia Liu at Yale University; Xiaokun Gu at Shanghai Polytechnic University; and Hezhu Shao at Wenzhou University.
This work was done with support from the National Science Foundation, under grants 1943813, 2154791, 2143642, 2311573 and 2521954; the U.S. Department of Energy, under grant DE-SC0020992; the Office of Naval Research, under grant N000142012155; and the Goodnight Innovation Distinguished Professor Endowment.
