Molecular Dynamics Simulations of Tension Amplification in Tethered Bottle-brushes

Bottle-brush polymers are grafted comb polymers in which the density of side chains grafted to the polymer backbone is large enough that steric repulsions between the side chains force the backbone to stretch and preclude it from forming random-coil configurations. Tethering one end of the bottle-brush backbone to a solid substrate restricts the conformations of the side chains near the surface and leads to side-chain repulsion that induces significant amplification of the tension along the polymer backbone. Depending on the grafting density on the substrate, the density of side chains and the length of the side chains, this tension amplification may be large enough break bonds along the bottle-brush backbone, especially at the site of the link with the substrate, where the tension is maximized. We have performed coarse-grained molecular dynamics simulations to understand the interplay between the factors affecting backbone tension amplification and whether the amplification effects can be controlled in such a way as to predict, for a given architecture and surface coverage, the maximum allowable packing of chains on the substrate surface prior to tethering failure.