Superhydrophobic (SH) surfaces have tremendous applications potential for essentially non-contact water and aqueous solution processing aboard spacecraft for life support. However, such surfaces have not been aptly exploited aboard spacecraft to date. In our Phase I work we (1) successfully demonstrated the marked improvements in system performance that can be achieved in microgravity environments with the use of SH surfaces, (2) we identified the many life support systems that can benefit from such surfaces, (3) we identified and documented an exhaustive variety of SH monolithic materials and coatings suitable for spacecraft deployment with holistic considerations of the complete life support system, and (4) we designed, constructed, low-g demonstrated, and delivered a high-performance passive urine collection and transport device. We also (5) devoted a significant effort to demonstrate the impact of surface contamination and fouling for 8 substrates during 57-day trials. The impact of the SH surface is to render the ‘wetted parts’ largely untouched by the contaminated urine streams. The result is that the device remains ‘contaminant-free’ and the number of replacement hoses can be substantially reduced or eliminated saving on cost, mass, volume, and crew time. We intend to develop and deliver a flight certified urine receptacle/hose device to NASA for flight tests aboard the ISS. Our long term objective is to deploy our manufacturing capabilities and judiciously apply the overall approach to any number of water processing unit operations for life support including urine collection and distillation elements, bubble separations, droplet/mist filters, plant watering systems, condensing heat exchangers, and more. The design approach provides a dramatic reduction of fouling and contamination in the microgravity environment because urine jets and drops simply rebound from the internal non-wetting surfaces without making physical contact.
In general, spacecraft are replete with applications for superhydrophobic surfaces including potable water storage and transport, hydrolysis for breathing oxygen, condensing heat exchangers, urine processors, portable life support systems, laundering and hygiene, food rehydration and dispensing, plant and animal habitats, and others. In fact, nearly all liquid systems on spacecraft might benefit from such wettability gradients: coolants, water, aqueous solutions, bio-fluids, experimental fluids, lubricants, propellants, and fuels.
We expect the resulting products to appeal to commercial space operators and as well as certain terrestrial markets. Potential products include passive bubble diverters, passive two-phase flow separators, low pressure-drop distillation systems, and the novel combination of complex geometry in the superhydrophobic non-wetting state: non-occluding conduits, fittings, and valves.