Zhang, Jianhui; (2024) Robust nanoengineered surfaces using reticular materials. Doctoral thesis (Ph.D), UCL (University College London).

Text Jianhui Zhang-Thesis-E copy.pdf - Accepted Version Access restricted to UCL open access staff until 1 January 2026. Download (14MB)

Abstract

Nature-inspired nanoengineered surfaces with superwettability, such as superhydrophobic and slippery lubricant-infused porous surfaces (SLIPS), have been investigated widely. A key reason is the potential for widespread applications in areas such as contamination prevention, anti-icing, anti-fouling, nanogeneration (of energy), and more. However, such non-wetting surfaces tend to be mechanically fragile and/or thermodynamically unstable, limiting their use in practical engineering applications. This thesis focuses on improving robustness and functionality by incorporating emergent reticular (porous) materials such as metal-organic frameworks (MOFs) and covalent organic frameworks (COFs). These materials are known to offer ordered, sub-nanoscale pores, rich chemical tunability, and design flexibility. The thesis shows how these features can be exploited to improve function of various non-wetting surface applications. To start with, an anti-icing, superhydrophobic coating was prepared using hydrophobic MOF nanoparticles and supramolecular polyurethane, demonstrating excellent self-healing under heating. The surface could also be infused with silicone oil (lubricant) to obtain SLIPS with low ice adhesion. However, although lubricant depletion occurred readily which is well known issue for such surfaces. The need for thermal treatment for self-healing of dry superhydrophobic surfaces and lubrication depletion were thus targeted next. To achieve room-temperature self-healing and all-day icephobicity, a photothermal superhydrophobic coating was prepared by adding carbon nanotubes (CNTs) decorated with surface-grown MOFs, i.e. MOF coated CNTs, as a filler in a self-healing matrix of polydimethyl siloxane. These coatings benefitted from an interfacial nanoconfinement effect from the sub-nm MOF pores to achieve a passive ice nucleation delay. Next, we show that a rational combination of MOFs (with suitable pores size), pore functional group and lubricant molecules can be used to realize a robust SLIPS with unprecedented durability in complex dynamic environments, such as under long-term droplet shedding and high-speed liquid jet impacts. The combination of MOF and lubricants formed an unconventional supramolecular structure via host-guest interactions which helped anchor lubricant molecules in MOF. Following this we focussed on overcoming the chemical susceptibility of MOFs by developing a solid slippery COF surface with nanoprecision roughness and optical transparency. A simple solid-vapour interfacial polymerization followed by post-synthetic silanisation with rationally selected silanes enabled the development of a slippery surface with nanoprecision texture. The resulting nano-confinement effect could be exploited to delay nucleation of CaCO3 and water on these COF surfaces. The phenomenon was also investigated through ab initio molecular dynamics, which helped understand experimental results. Finally, as novel example of use of such surfaces to tackle the interlinked energy and water crises, we developed a dew nanogenerator which combined radiative cooling and triboelectric nanogeneration (energy production). The system therefore enabled a simultaneous and passive harvesting of water and electricity production. Overall, the thesis offers a series of new insights into advancing surface nanoengineering and underscores the promise of such surfaces in realising sustainable development.

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