Schmidt, Malica Marleen; (2023) Nature-Inspired, Multifunctional Surfaces for Sustainable Life-Support in Extreme Environments on Earth and in Space. Doctoral thesis (Ph.D), UCL (University College London).

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Abstract

Ensuring human survival requires access to water, food, and a habitable environment. However, these resources are becoming increasingly scarce due to climate change and population growth. The resources are even more limited in extreme environments on Earth and in space, and Environmental Control and Life-Support Systems (ECLSS) are required to sustain human life. Current ECLSS, including those on the International Space Station (ISS), provide insufficient water recycling capabilities and rely on costly resupply, which is not feasible for future human spaceflight missions to the Moon and Mars. Additionally, excessive relative humidity, local moist areas, and microbial contamination pose risks to crew health and habitat integrity. Regenerative ECLSS offer a promising solution by enabling food generation, O2 production, CO2 breakdown, and bio-recycling of water and organic matter. However, these systems are still in the demonstration phase, and novel technologies are required for improved efficiency, sustainability, and reliability. This research focuses on the development of Nature-Inspired, Multifunctional Surfaces (NIMFS) to support ECLSS in extreme environments. Inspired by nature, the NIMFS exhibit multiple properties, with water and microbial absorption and transport, as well as microbial reduction as the primary functions. The surfaces were fabricated, using direct laser writing, and assessed through ground-based and microgravity experiments during parabolic flights and inside the ISS. The NIMFS demonstrated hydrophobic characteristics, with adhesive droplet behaviour in Wenzel state and up to ~50% higher contact angles compared to a flat surface. Over time, receding angles were observed due to water and microbial intake, as well as multilateral fluid flow into up to ~70% of the microstructures and channels, covering ~44% of the total surface area. In microgravity, enhanced capillary action facilitated the intake with increased speeds of up to ~54%, confirmed with a 100 times smaller Bond number. Secondary functions of the NIMFS involve light guidance and mechanical strength by adapting the surface geometry and material. Additional exploratory functions include ionising radiation shielding and the integration of organisms, resulting in water filtration, light generation, O2 production, and CO2 reduction. The results of this research aim to improve human health and comfort in extreme environments, reduce the energy consumption for freshwater conservation in terrestrial and space applications, and contribute positively to addressing climate change.

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