Nonmonotonic adsorption behavior of semiflexible polymers

Abstract

We study the adsorption behavior of semiflexible polymer chains with finite concentrations onto a structureless, planar, and impenetrable surface using polymer density functional theory based on a discretization of the Kratky-Porod wormlike chain model. Adsorption characteristics are investigated at different attractive interactions between the surface and polymers of various intrinsic stiffnesses. We analyze the density distributions in the vicinity of the surface and find, in the adsorption regime (when the surface attraction is strong: ϵw≳ϵw c, where ϵw c is the critical surface potential of adsorption transition), a nonmonotonic adsorption behavior for polymer chains with various intrinsic stiffnesses: the adsorption amount first decreases and then increases with the intrinsic stiffness, and the minimum adsorption amount (as well as the maximum critical surface potential of adsorption transition) occurs at lp ∼ Δ (Δ and lp are the attractive range of surface potential and persistence length, respectively), while in the depletion regime (ϵw≪ϵw c), the depletion depth and range are increased monotonically with the intrinsic stiffness. Furthermore, we find βϵw c∼lp/Δ-0.185 for lp ⋗ Δ and βϵw c∼lp/Δ0.366 for lp < Δ.