Stretching an adsorbed polymer globule

TL;DR

This study uses molecular dynamics to analyze how an adsorbed homopolymer in a poor solvent responds to stretching, revealing force-extension behavior and the effects of substrate interaction strength.

Contribution

It introduces a theoretical model that predicts force-extension relations and detachment forces for adsorbed polymers under different adsorption regimes.

Findings

Force reaches a plateau at large extensions.

Plateau force increases linearly with substrate interaction energy in strong adsorption.

Polymer globule deforms elastically in weak adsorption, with layered structure.

Abstract

Using molecular dynamic simulation, we study the stretching of an adsorbed homopolymer in a poor solvent with one end held at a distance $z_e$ from the substrate. We measure the vertical force $f$ on the end of the chain as a function of the extension $z_e$ and the substrate interaction energy $w$. The force reaches a plateau value at large extensions. In the strong adsorption limit, we show that the plateau value increase linearly in $w$ in good agreement with a theoretical model. In the weak adsorption limit, a polymer globule with a layered structure is formed and elastically deformed when stretched. In both cases a simple theoretical model permits us to predict the relation between the necessary force to fully detach the polymer and its critical extension.