Nanoengineering surface wettability via metal-phenolic networks

Abstract

Surface engineering is extensively involved in many industrial processes as well as diverse research applications including the engineering of catalysts, nanoparticles, coatings, membranes, gels, and other materials. In general, the purpose of surface engineering is to alter the physical or chemical surface properties on the molecular, nano-, micro-, or macroscale in order to target desired applications. Surface wetting, a ubiquitous natural interfacial phenomenon, is one of the most important yet least understood surface properties useful for addressing a broad range of practical and scientific issues. Surface wetting is also important for various global challenges such as the emerging energy and environment crises, and various health and safety concerns. One particularly “hot” scientific topic surrounding surface wetting is engineering coatings to render surfaces with tailored wettability, including coatings that are hydrophilic, hydrophobic, oleophobic, responsive, or versatile.

Metal-phenolic networks, coordination assemblies between metal ions and polyphenols, are emerging conformal coating materials useful for versatile surface engineering, including the engineering of nanomaterials and bio-interfaces. Polyphenols, which are abundant in natural sources as well as synthetic chemicals, have outstanding physicochemical properties besides metal chelation, such as reactive chemical groups, special interfacial interactions, and controllable bioactivity, and thus provide vast potentials in the field of advanced surface modifications. However, the potential of polyphenols in surface wetting has rarely been investigated, leaving the fundamental understanding necessary for advanced surface design and surface wetting largely unclear and incomplete. Therefore, this thesis aims to provide an overview of the wetting potential of metal-phenolic networks and to provide fundamental understandings for engineering advanced surface wetting. Specifically, this thesis investigates engineering surfaces on the levels of chemical structure, coating composition, and substrate hierarchy. Finally, some emerging applications for metal-phenolic networks with tailored surface wetting are presented.

The scope of this thesis is the engineering and exploitation of the surface wetting of metal-phenolic networks. The wetting fundamentals of metal-phenolic networks are first explored through the systematic study of coatings prepared from a wide range of polyphenolic ligands and a collection of metal ions on diverse substrates utilizing a series of coating methods. The intrinsic wetting properties, together with the active surface nature, were then successfully exploited for various applications including catalysis, oil-water separations, air filtration, and self-cleaning. The toolbox applicable building blocks for making metal-phenolic materials was enlarged by introducing the concept of host-guest chemistry—host functionality is incorporated into metal-phenolic networks where guest molecules can specifically bind with the host motifs within the surface coating. In addition to the facile control over surface wetting and specific binding, the host-guest metal-phenolic networks can also potentially help tackle incompatibility problems encountered in the design of materials for advanced interfacial interactions. Finally, dynamic metal-phenolic networks capable of adaptively interacting with a range of liquids were engineered. The resultant adaptive surface wetting, along with the broad wetting potentials of the metal-phenolic networks, is expected to contribute to the engineering of advanced surface coatings and find applications in other fields requiring tunable interactions.