Wetting Dynamics of 2D Interface Materials and Metal-Organic Frameworks


Student thesis: Doctoral Thesis

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Award date9 Jan 2020


Since the discovery of graphene, nanomaterials have received tremendous research interest due to their extraordinary physical and chemical properties, such as ultrathin thickness, high surface area, excellent electrical and thermal conductivity. Nanomaterials are of scientific significance in versatile applications, including nano-electronic and optoelectronic devices, energy conversion and storage. Most of these applications involve the elegant interplay of these nanomaterials with the ambient conditions such as air and liquid. For those conformal coatings and nano-devices, the water wetting ability exerts strong influences on material properties including uniformity, crystallinity, thermal stability and photoelectric property, thus impacting overall performances ultimately. Therefore, this thesis is to explore the fundamental wettability of the nanomaterial and develop nanomaterial induced structures with tailored properties, which may have potential applications in anti-aging, heat transfer and water harvesting.

Two-dimensional (2D) transition metal dichalcogenide (TMD) is one family of these emerging nanomaterials. The way how TMDs materials such as WS2 and MoS2 interact with dynamical environments dictates many important applications. Previous studies have suggested that these materials are susceptible to the aging effect due to the airborne contaminations. However, it is not clear whether such a hydrophilic-to-hydrophobic wetting transition is general to other materials and different substrates. Thus, in the first part of the thesis, we systematically investigate the evolution of wetting properties of 2D layered InSe film of different layers on different substrates, and reveal a general, but more pronounced hydrophilic-to-hydrophobic wetting transition of 2D materials. We experimentally identify the specific adsorbed species and theoretically reveal the intricate interplay between hydrocarbon contaminations and wettability. The aging effect and mechanism we reveal would shed light on the 2D material induced coatings for a wide range of applications in industry.

Another material, which possesses stable physio-chemical property and high water adsorption capacity, namely porous metal–organic frameworks (MOF) has been recently proven to be effective in capture, storage and separation of gas, heterogeneous catalysis and water harvesting. Despite extensive progress of MOF structures in the relatively normal conditions, our ability to give full scopes of MOF at extreme conditions, especially at the temperature below dew point remains limited. In this regard, we design a novel hierarchical multiscale structure with an uppermost MOF coating that yield a global hydrophobicity as well as partial hydrophilic nucleation sites. By harnessing the heterogeneous wettability, high water adsorption of porous MOF and hierarchical roughness feature in the multiscale structure, the droplet nucleation density, growth rate and overall heat transfer efficiency in the condensation system are effectively enhanced. The synergetic coupling of MOF and multiscale structures can find potential applications in surface engineering, adsorption-based heat pumps, water dehumidification and so on.

In addition to further advancing the MOF with high water adsorption into practical use, we develop a novel approach to encapsulate the MOF crystals into a matrix. The macroscopic structure is a composite involving an alginate induced spherical bead incorporated with a mixture of calcium chloride and MOF-MIL101(Cr). With an approximate diameter of 2 mm, the matrix is capable to generate 0.5 kg kg-1 water adsorption from air at 9.5 mbar water vapor pressure and 25 °C. More intriguingly, the matrix can not only inhibit high water uptake stability in adsorption/desorption cycles without additional input of energy, but also outperform other conventional adsorbents in terms of mechanical and chemical stability. Leveraging all the poses, we believe that our new MOF-derived matrix will open up new and exciting vistas in water harvesting, energy conversion and refrigeration field.

    Research areas

  • 2D Interface, Metal-Organic Frameworks, Wetting, wetting aging effect, water harvesting