Self-Assembled Monolayers at the Solid-Liquid Interface: Design, Post-Modification and Effects of Molecular Variations as Compared to Homogenous Systems

Abstract

Since the dawn of chemistry, the study of reactions has taken place in homogenous systems. There is a wealth of knowledge relating to the kinetics and thermodynamics of such reactions. However, the increasingly smaller materials used in today’s advancing technology requires novel heterogeneous chemistries at solid-liquid interfaces. Control over surface chemistry has numerous applications, including increasing biocompatibility for medical use, catalysis, improving cosmetic products and developing novel electronic devices. As we move toward a world with self-healing materials, single molecule circuits and nanoscale machines, the ability to attach molecules to a surface in a well-organized fashion is increasingly important.

Astoundingly, under appropriate conditions, single molecules self-arrange into highly ordered nanomaterials using guidelines internally coded by its elements and their arrangement in the molecule. Being able to exploit self-assembly is invaluable to successful fast-paced engineering of nanomaterials. However, quantifying the interplay between forces and developing a predictive model for 2D self-assembly is to date unsolved. An additional question that largely remains unanswered is, to what extent can relationships known from homogenous chemistry aid in understanding the self-assembly of heterogeneous systems? The work in thesis was motivated by these fundamental problems.

This thesis includes studies of both physisorbed and chemisorbed systems. Chapters 3 and 4 explore the effect of H-bonding and van der Waals interactions on physisorbed self-assembled monolayer (SAM) morphology using a series of 5-alkoxyisophthalamides and 5-alkoxyisophthalic acids on HOPG. The relationship between self-assembly in heterogeneous versus homogenous phases was examined in Chapter 3 and continued in chemisorbed systems in Chapter 5. The results of substituent effects on formation kinetic studies of chemisorbed styrene SAMs on H-Si fit to equations quantifying substituent effects in homogenous reactions. These studies provide evidence for the success in applying well quantified homogeneous relationships to lesser explored chemistry at a solid-liquid interface.

As interest in unique surface functionalization grew, this thesis expanded to include collaborations requiring surfaces exhibiting specific properties. These projects, described in Chapter 6 and 7, include surface assemblies for fullerene bombardment and SAMs for quantum control experiments. The design, post-modification and characterization of Si-phosphonate and Au-carbene linked SAMs for designated applications are presented.