Tension enhancement in branched macromolecules upon adhesion on a solid substrate

Abstract

The effect of self-generated tension in the backbone of a bottle-brush (BB) macromolecule, adsorbed on an attractive surface, is studied by means of Molecular Dynamics simulations of a coarse-grained bead-spring model in the good solvent regime. The BB-molecule is modeled as a backbone chain of $L$ beads, connected by breakable bonds and with side chains, tethered pairwise to each monomer of the backbone. Our investigation is focused on several key questions that determine the bond scission mechanism and the ensuing degradation kinetics: how are frequency of bond scission and self-induced tension distributed along the BB-backbone at different grafting density $\sigma_g$ of the side chains? How does tension $f$ depend on the length of the side chains $N$, and on the strength of surface adhesion $\epsilon_s$? We examine the monomer density distribution profiles across the BB-backbone at different $\epsilon_s$ and relate it to adsorption-induced morphological changes of the macromolecule whereby side chains partially desorb while the remaining chains spread better on the surface. Our simulation data are found to be in qualitative agreement with experimental results and recent theoretical predictions. Yet we demonstrate that the interval of parameter values where these predictions hold is limited in $N$. Thus, at high values of $\epsilon_s$, too long side chains mutually block each other and freeze effectively the bottle-brush molecule.