Angle-Dependent Atomic Force Microscopy Single-Chain Pulling of Adsorbed Macromolecules from Planar Surfaces Unveils the Signature of an Adsorption–Desorption Transition

Abstract

The adsorption–desorption behavior of polymer chains is at the heart of macromolecular surface science and technology. With the current developments in atomic force microscopy (AFM), it has now become possible to address the desorption problem from the perspective of a single macromolecule. Here, we report on desorption of single polymer chains on planar surfaces by AFM-based single molecule force spectroscopy (SMFS) as a function of the pulling angle with respect to the surface-normal direction. SMFS experiments were performed in water with various substrates using different polymers covalently attached to the AFM probe tip. End-grafting at the AFM tip was achieved by surface-initiated polymerization using initiator functionalized tips. We found that the desorption force increases with a decreasing pulling angle, i.e., an enhanced adhesion of the polymer chain was observed. The magnitude of the desorption force shows a weak angular dependence at pulling angles close to the surface normal. A significant increase of the force is observed at shallower pulling from a certain pulling angle. This behavior carries the signature of an adsorption–desorption transition. The angular dependence of the normalized desorption force exhibits a universal behavior. We compared and interpreted our results using theoretical predictions for single-chain adsorption–desorption transitions.

Thin Polymer Film Force Spectroscopy: Single Chain Pull-out and Desorption

“…This suggests that the peak represents a phenomenon where the SBR chains are desorbed from the substrate, but are not completely removed from the film. This is more likely to occur when the polymer chains have long loop and tail conformations next to trains, that is, adsorbed chain segments. , The desorption of a train segment will result in a step with a value equal to the force associated with substrate desorption, as long as the rest of the polymer chain is still adsorbed to the substrate (by other segments) and, at the same time, still embedded within the film. Such desorption of individual train segments is fairly common on the mica, but not on the silicon or graphite.…”

Polymer single chain imaging, molecular forces, and nanoscale processes by Atomic Force Microscopy: The ultimate proof of the macromolecular hypothesis

“…5H. Here, train-like desorption force curves are depicted at different pulling angles, with the angle values shown below the scheme of the experiment [65]. A systematic experimental study allowed us to interpret the directional dependence of the desorption forces using a molecular theory, including pulling-angle-dependent desorption-adsorption transitions [75,76].…”

Angle-dependent strength of a single chemical bond by stereographic force spectroscopy

“…S1 †). [13][14][15] Note that several potential confounding effects, such as vertical or lateral deections and torsions of the cantilever, as well as the accuracy of the piezo system, may induce errors in stereographic pulling. We have largely eliminated these effects in our experiments and shown that the remaining uncertainties are negligible.…”