Unraveling the Effect of the Structure of Surfaces Having Attached Polymer Chains on the Adhesion Behavior

ABSTRACT Chain stretching, interpenetration, and entanglement are crucial for adhesion between polymer surfaces and the performance of adhesives, fiber‐reinforced composites, self‐healing polymers, and elastomers. The goal of this work was to study the effect of different structural parameters of surfaces containing attached polymer chains on these phenomena in order to design adhesives and self‐healing polymers, among others, with improved performances. To this end, atomic force microscopy was used to measure the forces between surfaces with attached poly(tetramethylene oxide)‐based soft polyurethane chains. Chains were grafted onto both an atomic force microscopy probe and the impenetrable surfaces of inorganic substrates with varying areal densities. Results showed that the density of grafts fundamentally affected the adhesion process between the grafted surfaces. Larger adhesion forces were observed for surfaces with lower values of areal density of grafts due to interpenetration. Thus, applications (adhesives, composite interfaces, etc.) that depend upon adhesion should pursue high levels of chain interpenetration. The atomic force microscopy results were successfully fitted to the ideal rubber elasticity theory. This suggests that the experimental setup allowed the unraveling of many factors associated with the behavior of interacting soft polymers: affine deformation, chain stretching, temporary crosslinks, and the random coil conformation of polymer strands.