PEO-Grafted Gold Nanopore: Grafting Density, Chain Length, and Curvature Effects

Polymer-grafted nanopores have found various nanotechnological applications such as separation membranes and nanopore-gated control of materials transportation (e.g., nanofluidic devices). The morphological change of the grafted polymers facilitates precise control of materials transportation, making them promising in numerous fields. In order to design these nanomaterials with desired properties, a good understanding of the structural and hydration properties of grafted layers and the interaction between polymers and solvents is essential. Here, by atomistic molecular dynamics simulations of poly(ethylene oxide) grafted gold nanopore, we elucidate the effects of polymer grafting density and chain length, as well as the curvature of the nanopore on the properties of the grafted PEO layer. We show that the polymer layer starts from an adsorbed pancake shape at a low grafting density, transitions to a mushroom-like or overlapped chain at a moderate grafting density, and to a densely packed brush at a high grafting density. Correspondingly, PEO transforms from a well-hydrated state to a dehydrated state when grafted at low to high grafting densities. The layer thickness follows the scaling found in a planar brush when the height is less than the pore radius (weak confinement) while when confined in a nanopore with high curvature, PEO chains rearrange themselves into a conical shape (strong confinement). Different regimes of polymer layers have been identified and a unified diagram of states is provided which could be used as guidance for polymer-grafted nanopore design.