Conformational Studies of bottle-brush polymers absorbed on a flat solid surface

Abstract

The adsorption of a bottle-brush polymer end-grafted with one chain end of its backbone to a flat substrate surface is studied by Monte Carlo simulation of a coarse-grained model, that previously has been characterized in the bulk, assuming a dilute solution under good solvent conditions. Applying the bond fluctuation model on the simple cubic lattice, we vary the backbone chain length $N_b$ from $N_b=67$ to $N_b = 259$ effective monomeric units, the side chain length $N$ from N=6 to N=48, and the grafting density $σ=1$, i.e., parameters that correspond well to the experimentally accessible range. When the adsorption energy strength $ε$ is varied, we find that the adsorption transition (which becomes well-defined in the limit $N_b \rightarrow \infty$, for arbitrary finite $N$) roughly occurs at the same value $ε_c$ as for ordinary linear chains (N=0), at least within our statistical errors. Mean square end-to-end distances and gyration radii of the side chains are obtained, as well as the monomer density profile in the direction perpendicular to the adsorbing surface. We show that for longer side chains the adsorption of bottle-brushes is a two step process, the decrease of the perpendicular linear dimension of side chains with adsorption energy strength can even be non-monotonic. Also the behavior of the static structure factor $S(q)$ is analyzed, evidence for a quasi-two-dimensional scaling is presented, and consequences for the interpretation of experiments are discussed.