Quantitative nanoscale analysis of polymeric materials and their interactions with solvents using scanning force microscopy

The goal of this project was to study the frictional and adhesive interactions between AFM probes and surfaces. Poly(2-dimethylamino)ethyl methacrylate) (PDMA) and poly(glycerol penta(ethylene oxide)methacrylate) (PAGEO5MA) polymer brushes were synthesized to investigate them and examine the impact of grafting density on the constant formation of hydrogen bond complexes in different medium.
This study comprehensively examines the frictional behaviour of PDMA brushes fabricated across various scales, from nanometers to micrometers, using Friction Force Microscopy (FFM). The investigation reveals how solvent interactions influence frictional properties, with water promoting adhesion-dominated, sublinear friction-load relationships, while ethanol induces polymer collapse and linear friction-load relationships governed by molecular ploughing. The findings highlight that smaller PDMA features exhibit reduced adhesion and lower friction coefficients in water, whereas ethanol causes densely packed, collapsed polymer structures, increasing resistance to mechanical deformation, and enhancing the ploughing effect. These insights deepen our understanding of the frictional dynamics of polymer brushes and their dependence on environmental conditions and polymer characteristic.
This research examines the synthesis of PDMA brushes via Surface-Initiated Atom Transfer Radical Polymerization (SI-ATRP) and their frictional behaviours as influenced by varying grafting densities. The brush conformation was found to be significantly dependent on grafting density and the surrounding environment. Friction forces were analysed into load-dependent and shear-dependent components, revealing how normal and lateral forces affect the interactions between an AFM tip and PDMA surfaces. At high grafting densities, extensive contact leads to adhesive sliding, while lower densities result in fewer contact points and ploughing mechanisms. These findings, supported by modelling the friction-load relationship, indicate shifts in polymer chain conformations and underscore the complex relationship between grafting density and frictional properties.
This research explores the fabrication of PAGEOMA brushes through Surface-Initiated Activator Regenerated by Electron Transfer Atom Transfer Radical Polymerization (SI-ARGET ATRP) and their frictional behaviours across varying grafting densities. The brush conformation significantly influences grafting density and the surrounding environment, which in turn affects the physical properties of PAGEOMA brushes. Friction forces between an AFM tip and the PAGEOMA surface are categorized into load-dependent and shear-dependent terms, determined by normal and lateral forces, respectively. High grafting densities lead to extensive contact and adhesive sliding, while lower densities result in fewer contact points and a transition to ploughing mechanisms. Variations in surface shear strength (τ) indicate shifts from brush-like to mushroom or pancake configurations. These findings are crucial for optimizing PAGEOMA brush-based materials for applications in coating, surface treatment, and medical materials by understanding the relationship between grafting density and frictional properties.