Expanding the Scope of Bidentate Adsorbate Monolayer Films on Gold Materials and their Applications



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The ability of materials engineers and surface scientists to control the properties of metal surfaces at the nanoscale is critical. Among the methods developed to achieve such control is the use of self-assembled monolayers (SAMs), which have found widespread application in a variety of fields ranging from biologically relevant surfaces to lubricants for microelectromechanical systems (MEMs) and corrosion inhibitors. Among the various types of SAMs, the most studied systems involve the use of alkanethiols on gold substrates due to their ease of preparation, inertness, strong Au–S interaction with a bonding energy of 50 kcal/mole, and well-defined structural features. However, SAMs based on monodentate alkanethiols are only moderately stable. The introduction of multidentate headgroup architectures (e.g., bidentate and tridentate adsorbates) offers enhanced substrate-adsorbate bonds and the formation of chemically and thermally stable SAMs, particularly for bidentate adsorbates, due to the good balance of stability and crystallinity/packing density. The "chelate effect" is responsible for the increased stability conferred by multiple bonding moieties. Despite the increased stability provided by bidentate adsorbates, several disadvantages must be addressed: (1) a limited ability to fine-tune tailgroups containing two chemically distinct functional groups within a single molecule; (2) a low packing density of films generated from bidentate adsorbates having sterically bulky headgroups; and (3) a low thermal stability due to the facile formation of intramolecular disulfides. The aim of this dissertation is to synthesize and characterize bidentate adsorbates on an Au substrate for the purpose of improving the performance of monolayer thin films and their application toward nanoscale anti-fouling surface coatings. The first study reports on the use of the "chelate effect" in conjunction with mole-fractional control of the adsorbate to generate stable nanoscale coatings with readily tunable interfacial properties. Additionally, this dissertation describes the design and synthesis of new classes of bidentate adsorbates by modifying the spacer unit with an olefin linker unit to create organic thin films with similar film properties to n-alkanethiol thin films. Additionally, the third set of studies in this dissertation discusses the synthesis and characterization of modulating bidentate monolayer thin films using an asymmetric headgroup between thiol and cyanide moieties to create highly stable organic thin films. The final section of this dissertation discusses possible applications of these adsorbates for the generation of antifouling interfaces. All the organic thin films prepared in this dissertation, including mixed phase-incompatible SAMs, olefin-linker-based SAMs, and modulating bidentate adsorbates with headgroup asymmetry, are promising materials for enhancing thin-film capabilities as adhesion-resistant nanoscale coatings.



self-assembled monolayers, surfaces, interfaces


Portions of this document appear in: Sakunkaewkasem, Siwakorn, Maria D. Marquez, Han Ju Lee, and T. Randall Lee. "Mixed Phase-Incompatible Monolayers: Toward Nanoscale Anti-adhesive Coatings." ACS Applied Nano Materials 3, no. 5 (2020): 4091-4101; and in: Sakunkaewkasem, Siwakorn, Mario A. Gonzalez, Maria D. Marquez, and T. Randall Lee. "Olefin-Bridged Bidentate Adsorbates for Generating Self-Assembled Monolayers on Gold." Langmuir 36, no. 36 (2020): 10699-10707.