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

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, σ eff , 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.

Polymer Brushes on Silica Nanostructures Prepared by Aminopropylsilatrane Click Chemistry: Superior Antifouling and Biofunctionality

“…The 2 kg/mol PEG chains are small enough to assemble quite densely on the surface (0.51 nm –2 ) but the brush does maintain a degree of hydration (at least 80% on a planar surface as shown above). The pore geometry may contribute to a slightly increased volume fraction of polymer when the radius is smaller than the expected brush extension . Considering all these factors together, the conductance changes seem very reasonable for pores with walls coated by a few nm of compact APS-SMCC and the rest of the volume containing hydrated PEG.…”

polyGraft 1.0: A program for molecular structure and topology generation of polymer‐grafted hybrid nanostructures

“…In addition, the backbone topology and side chain length affect the structural and hydration properties, revealed by atomic MD simulations using the structure and topology generated by polyGraft. 50 Apart from the backbone topology and chain length of backbones and grafts, the grafting density is also an important parameter determining the structural properties of bottlebrush polymers. To accommodate for this factor, polyGraft can generate molecular structures with various grafting densities, as shown in Figure 5D.…”

“…experiments or theories alone are hard to address. Using MD simulations, polymer-grafted hybrid materials can be studied, such as polystyrene-grafted silica nanoparticle, 27 poly(L-lactic acid) grafted graphene brush, 28 poly(acrylic acid) grafted polyelectrolyte brush, 29 and PEO grafted gold planar/spherical/cylindrical brushes [30][31][32][33] using atomistic MD simulations, and polymer grafted nanoparticles using coarse-grained MD simulations. [34][35][36] Performing reliable MD simulations of these systems, however, is not trivial.…”

“…Therefore, a good starting structure is very important, for example, no close contact of composing atoms especially for hybrid systems with high grafting densities such as polymer-grafted nanopores. 33 Not only the starting structure, but the topology (and corresponding force field parameters) is also very important, which are usually obtained from carefully validated simulation tests against experiments or theories. It is therefore very clear that an MD simulation-oriented program is highly desired for automated generation of the molecular structure and topology of polymer-grafted hybrid materials.…”

Thermally Switchable Nanogate Based on Polymer Phase Transition

“…The design of bioinspired nanopores brings the ability to manipulate and control ionic and molecular transport inside a confined environment and provides insight into ionic and molecular transport processes of biological channels. − Synthetic nanopores have many advantages over biological ones, such as their stability, tunable dimensions (size and shape), and the possibility of integration into nanofluidic systems. , By functionalizing the surface of the nanopore, their physical and chemical properties (e.g., hydrophobicity, selectivity, surface charges, and specific molecular recognition) and thus the ionic and molecular transport properties can be modified ,− and modeled using simulations. − …”