Structure of bottlebrush polymers end-grafted to a planar surface

Polymer brush is a hybrid material composed of a solid substrate coated with end-grafted polymers. We conducted coarse-grained molecular dynamics simulations and scaling theory of the equilibrium structure of planar brushes formed by bottlebrush polymers. Bottlebrushes are branched macromolecules consisting of densely spaced linear side chains grafted along a central (linear) backbone. We elucidate the relationship between bottlebrush architecture, surface coverage σ and polymer brush thickness H. We study the impact of three length scales on the brush height H: D₀ , the cross-section radius of bottlebrushes determined by the degree of polymerization of side chains N_sc , R₀ the (overall) size of bottlebrushes controlled by the degree of polymerization of backbone N_bb and d the distance between nearest-neighbor tethering sites. The latter quantity provides a measure of molecular coverage σ of a substrate defined as the number of bottlebrush polymers per unit surface area σ ∝ 1/d² . Our theoretical analysis identifies three conformational regimes for the height H, which gradually establish upon increasing substrate coverage and stem from interplay between relevant length scales: d, D₀ and R₀.