MCE: EAS Trailblazers Department Seminar

Mechanical and Civil Engineering Seminar Series

Title: Physics and Engineering of Extremely Moisture-Capturing Hydrogels for Freshwater Production and Energy Storage

Abstract: Humidity in the air is a vast water and energy resource available at any location. Air in the atmosphere contains six times more freshwater than that in all rivers and lakes. This moisture also carries over a thousand times more power than the global electricity demand. For over two centuries, numerous water sorbent materials have attempted to harness these resources. However, their performance, optimization, scalability, and durability have severely limited their potential. In this work, we demonstrate the material-level to application-level development of low-cost (<$1/kg of material) and durable (>8-month) hydrogel-salt composites that can capture record amounts of water from the air.

We first developed physics-based models that accurately predict the sorption and transport mechanisms in hydrogel-salt composites, enabling their targeted design and optimization. We leveraged these models to establish the fundamental connections between hydrogel chemical and mechanical properties with their sorption performance. We then used these insights to synthesize hygroscopic hydrogels with the highest capability ever demonstrated of any material to capture and store water from the air (~2 kg of water/kg of material), even in arid conditions (30% relative humidity). Beyond performance, we studied the hydrogel degradation mechanisms, probing an unexplored, yet critical parameter. Specifically, by preventing metal ion-mediated hydrogel degradation, we demonstrated >8-month material durability, exceeding previous state-of-the-art works and yielding novel insights into polymer degradation.

Finally, we have worked towards the integration of these materials into two devices: a passive atmospheric freshwater harvester that uses hydrogels to convert ambient moisture to drinking water and a thermal battery capable of storing and reusing air-conditioning waste heat via the hydrogel absorption enthalpy. Enabled by our models and rational syntheses, these devices promise to meet drinking water requirements per capita (>5 L/day) and to increase the coefficient of performance of air conditioning by >40%. Our rational, physics-based development of hydrogel-salt composites represents a significant step towards the utilization of ambient moisture and its energy to address grand humanity challenges.

Bio: Carlos D. Díaz-Marín is a PhD candidate in Mechanical Engineering at MIT. His work, under the supervision of Professors Gang Chen and Evelyn N. Wang, has utilized polymer physics, transport phenomena, and scalable hydrogel synthesis to push the performance limits of water capture from the air to enable large-yield freshwater production from the air and high energy density sorption-based energy storage. He obtained his M.S. in Mechanical Engineering from MIT (2021) and double B.S. degrees in Mechanical Engineering (2017) and Physics (2018) from the University of Costa Rica. Carlos is a Martin Family Sustainability Fellow and a selectee of the Mechanical Engineering Rising Stars (University of California, Berkeley, 2023) workshop.

NOTE: At this time, in-person Mechanical and Civil Engineering Lectures are open to all Caltech students/staff/faculty/visitors.