CAREER: Programmable Negative Water Adsorption of Bioinspired Hygroscopic Materials

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Hygroscopic materials typically absorb water and swell when the local relative humidity (RH) increases and then release water and shrink when the RH decreases. A counterintuitive phenomenon has been observed in trees, where they store water when the local environment is dry and deplete water when it is humid. Inspired by this natural phenomenon, the investigator will develop a new class of materials with negative water adsorption capabilities, such that water is released when the RH increases. This project will explore the opportunities for designing hygroscopic materials with programmable negative water adsorption properties. The research is expected to elucidate the underlying mechanisms of the counterintuitive phenomenon of negative water/gas adsorption. This knowledge will lead to breakthroughs related to dynamically regulating material properties and responsive soft condensed matter and reveal how nature designs different micro/nanofluidic systems to harness water evaporation as an energy source. The research will also enable the development of new low-cost water harvesting devices that autonomously collect water in a dry environment without using electrical energy. Educational activities are integrated with the research to promote K-12 students’ interest in STEM and increase the public’s understanding of scientific concepts. The educational activities include developing visible and touchable learning kits and competitions, allowing local students and New Yorkers to interact with state-of-the-art science engagingly. The negative water adsorption phenomenon is achieved when domains of materials with distinctive water-responsive actuation and cavitation characteristics are carefully integrated. A range of hygroscopic materials will be fabricated such that the confined water cavitation behaviors and material water responsiveness are systematically varied through changes to the confining geometry and surface chemistry. Using these materials/structures, the confining geometry and surface chemistry will be correlated with the confined water cavitation behavior. Additionally, the research will program hygroscopic material water-responsive actuation by tuning the properties of confined water. Negative water adsorption materials will be developed by integrating the domains of materials with distinct water-responsive and water cavitation properties. The overarching educational goal is to communicate the concepts and importance of natural water evaporation to students and the public. The City University of New York (CUNY) students will be taught through hands-on learning activities. The investigator will host an annual “Evaporation Energy Challenge” for local high school students and teachers and communicate evaporation science in public venues. The investigator will also redesign an interdisciplinary graduate-level course. The desired educational outcome is to ignite the students’ and the public’s excitement about the potential of natural evaporation as an energy source and attract talented and motivated students to pursue STEM careers.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.