PEO-Grafted Gold Nanopore: Grafting Density, Chain Length, and Curvature Effects
Guang Chen, Elena E. Dormidontova
Abstract
Polymer-grafted nanopores are used in several nanotechnological applications which demand control of structural and hydration properties of the grafted polymers. By means of atomistic molecular dynamics simulations, we systematically investigate the chain length and grafting density effects on the conformation and hydration of poly(ethylene oxide) (PEO) grafted to gold nanopores of different radii. We find that if the pore size exceeds the polymer length, increasing the grafting density or chain length for a given pore results in conformational changes of the polymer from pancake-like shapes to well-hydrated overlapping mushrooms to a denser less hydrated polymer brush. We demonstrate that an increase of pore curvature results in considerable polymer crowding within the pore, which translates into an increase of the effective grafting density, σeff, which has to be taken into consideration when concave nanopores and planar and convex surfaces are compared. We show that for a given polymer grafting density and chain length, a decrease in the pore radius R results in an increased radial orientation, and for a low grafting density, there is a slight increase of the grafted layer height H until the polymer chains fill the pore (R ∼ H) and start folding near the pore surface, conforming into a cone-shape with a further brush height decrease until the high-density limit is reached. The properties of polymer-grafted nanopores, such as water exchange and gating capability, depend on the polymer conformation and hydration, which are strongly influenced by the polymer grafting density and differ for polymer-filled and open nanopores.