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Microcontact Printing of N-heterocyclic Carbene Molecules Onto Gold Surfaces

This project was supervised by Dr. Hugh Horton from the Department of Chemistry at Queen’s University.

Self-assembled monolayers (SAMs) have extensive applications in chemical resistance, biocompatibility, nanofabrication, and control of wetting and adhesion. Particularly for metals, thiol-based SAMs have attracted widespread attention due to their simple preparation from gas or solution phases, as well as their high stability resulting from strong sulfur-metal bonds and intramolecular forces. The resulting monolayers possess molecular order and stability under ambient conditions. However, n-heterocyclic carbene SAMs are gaining stride as they show greater resistance to heat and chemical reagents, compared to the thiol-based SAMs, explained by the gold-carbon bond being stronger than the gold-sulfur bond. While considering this progress in creating more favourable SAMs, this project will incorporate hydrophilic NHCs onto gold surfaces using the microcontact printing process. This will be done following the work of Whitesides, with the end goal of designing lab-on-a-chip devices. The microcontact printing device will be made by chemically etching a pattern on to a silicon wafer, which acts as a mold for the PDMS liquid polymer. Once set, the polymer is peeled off the mold, becoming a patterned stamp to be coated with the molecule to be adsorbed on its surface. Air-stable bicarbonate salt-NHCs will be stamped onto a gold surface, replicating the desired pattern created by the chemical etching. X-ray photoelectron spectrometry as well as surface wettability measurements will be used to characterize the product. This project will demonstrate the proof of concept of microcontact printing with NHCs and allow for greater control over surface properties, compared to their thiol-based counterparts.