Session: Research Posters

Paper Number: 120263

120263 - Structural Radiative Cooling in Highly Reflective White Snail Shells as Adaptation to Extreme Heat Environments 

In recent years, a worldwide trend continues of record high temperatures, heat waves, and severe weather as the effects of climate change continue to manifest. With these changes comes an unprecedented need for populations to survive increasingly extreme environments and conditions, and as a result a pressing need to develop technologies to improve quality of life while avoiding further contributions to climate change in the form of fossil-fuel dependent or greenhouse gas emitting traditional cooling and heating technologies. Radiative cooling is a passive cooling technique utilizing the heat sink effects of low temperatures in deep space to create an energy exchange, allowing for surfaces on earth to cool several degrees below ambient temperatures even in direct sunlight without relying on technologies that further harm the environment. While many technologies utilizing radiative cooling have been developed in the form of coatings, films, and other integrated photonic structures, there is a source of inspiration for further innovations that has been largely unexplored: nature itself.

            Looking to nature for structures that have evolved over millions of years to survive their habitats, we can find examples of biological systems that utilize the same radiative cooling phenomena to cool themselves in severe heat environments. One such system is that of the strikingly white shell of Sphincterochila zonata, a desert snail that lives in the Negev desert of Israel where temperatures can reach extreme highs of 46 degrees Celcius on the hottest of days. Unlike other snail species living in this habitat, which survive using climbing or burrowing techniques, Sphincterochila zonata is known to remain visible in direct sunlight and instead utilize its white shell for cooling via reflection of solar irradiation. In this work, the structure of this shell is analyzed to understand how it achieves radiative cooling via a measured 90.8% total solar reflectance, a record high for a biological system. The porosity, nanostructure, and material composition are analyzed, and compared to relative biological systems in other white shells, including those living in the same Negev desert and highly contrasting ocean dwellers. Structural analysis demonstrates feature sizes of ~200 nm averages and layered platelet-like morphologies that optimize for light scattering in solar wavelengths. Furthermore, mechanical properties of the shell are optimized via the structure that features nanoscale air voids, which also contribute to light scattering, and organic chitin-based matrix materials creating a brick-and-mortar structural effect when interspersed between calcium carbonate nanoplatelet layers. This study aims to find inspiration for future developments of radiative cooling multifunctional technologies through understanding of how the structures of this phenomenal biological system contribute to optical properties, radiative cooling potential, mechanical robustness, and overall survival in its extreme environment.

Presenting Author: Andrea Felicelli Purdue University

Presenting Author Biography: Andrea Felicelli is a PhD student in Mechanical Engineering at Purdue University, working in the laboratories of Professor Xiulin Ruan and Professor George Chiu. Her work focuses on development, manufacturing, and bio-inspiration of nanocomposites and multifunctional materials with applications in cooling technologies.

Authors:

Andrea Felicelli Purdue University
Emily Barber Purdue University
Sultan Alnajdi Purdue Mall
Xiulin Ruan Purdue University
George Chiu Purdue University
Dror Hawlena Hebrew University of Jerusalem
Pablo Zavattieri Purdue University