Water-harvesting and self-cleaning on air/liquid independent surfaces (Solicitation: W911NF-17-S-0002)
Abstract
The uneven distribution of freshwater on the earth leads to severe water scarcity in some regions, such as part of the United States, northern Mexico, the Middle East, and northern Africa. However, the moisture in the air is widely distributed across all countries, so water harvesting from the air is one of the promising technologies. Even though electricity-based active water-harvesting technologies are commercialized to provide fresh and clean drinking water, the active technologies are far from optimization owing to a few weaknesses: (a) it consumes a lot of electricity, which is not available in impoverished regions, (b) the systems are complex and heavy, and (c) the fundamental mechanism of moisture capture and removal process is not well understood. Passive water harvesting consumes no external energy but can efficiently harvest water from air with optimized designs of surface topography and surface chemistry. There are two important processes in water harvesting: moisture nucleation and droplet removal. In nature, Namib desert beetles absorb tiny water droplets from the fog for their survival. The hydrophilic bumps on the beetle surface favor water capture and hydrophobic domains help to remove water droplets. A fundamental understanding at the molecular level will gain deep insights into the water-surface interactions and provide important rationales for the moisture-capturing materials design. Droplet removal is another significant process in water harvesting and is also critical for self-cleaning. Existing technologies rely on either patterned superhydrophobic surfaces (rely on air lubricant) or liquid infused surfaces (rely on liquid lubricant), resulting in lubricant displacement and unsatisfactory durability. A fundamental study of the interfacial mobility on air/liquid independent surfaces is critical for the materials design of water harvesting and self-cleaning. The goal of this proposal includes: (i) understanding the basic sciences of moisture nucleation and removal, (ii) providing fundamental rationales for materials design, and (iii) developing self-cleaning materials to mitigate surface contamination. The water-harvesting and self-cleaning surfaces have some common sciences at the liquid-surface interface. Unlike the air lubrication on superhydrophobic surfaces and liquid lubrication on liquid infused surfaces, we proposed to chemically bond mobile molecular chains on the solid surface for boundary lubrication. The grafted flexible polymers behave like a liquid lubricant for droplet removal. This enables air/liquid-independent surfaces for rapid droplet repellency and self-cleaning in durable operations. Moreover, the water harvesting surface needs both water-affinitive functional groups (e.g., -OH or -NH2) for moisture capture and water-repellent functional groups (e.g., -CH3 or -CF3) for droplet removal. While beetle-inspired surfaces use microscale hydrophilic/hydrophobic patterns, creating molecular scale hydrophilic and hydrophobic patterns can significantly optimize the rate of water harvesting. The moisture capture and repellency processes are also preferred in self-cleaning applications. The proposed non-sticky surface can capture water droplets can self-clean the dust and dirt. Our fundamental studies in water capture and repellency will elucidate the basic sciences for the materials design of durable water-harvesting and self-cleaning surfaces, in line with DoDÕs needs.
Document Details
- Document Type
- DoD Grant Award
- Publication Date
- Jul 24, 2019
- Source ID
- W911NF1910416
Entities
People
- Xianming Dai
Organizations
- Army Contracting Command
- United States Army
- University of Texas at Dallas