Investigating Nucleophilic Reactions of Organic Thin Films at the Molecular Scale Using Chemical Force Microscopy

Abstract

Surface reactions are central to many scientific and technological processes, including industrial catalysis, environmental remediation, and energy conversion. A detailed understanding of interfacial interactions at the nanoscale requires insight into the chemical, physical, and mechanical processes that govern surface behaviour. This thesis investigates the chemical interactions of functional organic thin films with defined surface terminations using chemically modified atomic force microscopy (AFM) probes in chemical force microscopy (CFM). The work addresses two objectives: first, to examine nucleophile–electrophile interactions and the influence of solvent media; and second, to investigate the tribological aspects of surface reaction kinetics. Chapter 3 uses force–distance measurements to quantify adhesion forces and elucidate probe–surface interactions. Chapter 4 uses lateral force microscopy (LFM), also known as friction force microscopy (FFM), to examine reaction-related frictional behaviour. Two hypotheses are tested: that CFM can measure interaction forces between nucleophiles and electron-deficient carbon centers, and that CFM can probe bond-formation processes during nucleophilic reactions. More than 64 systems, including silane- and thiol-based self-assembled monolayers, were examined. The results show that adhesion and friction forces increase with the mole fraction of reactive functional groups. Amino-functionalised surfaces exhibit pronounced time-dependent evolution, consistent with progressive interfacial chemical transformation. Distinct contributions from hydrogen bonding, van der Waals interactions, and covalent bond formation are identified, with adhesion enhanced in nonpolar environments. Notably, the nucleophilic-electrophilic reaction between the tip and the sample occurred within ~14 min.