Dielectric Effects on Ion Transport in Polyelectrolyte Brushes

Abstract

Surface-grafted polyelectrolytes provide a versatile way to create functionalized interfaces and nanochannels with externally controllable properties. Understanding the behavior of ions within the brush-like assemblies is crucial for the further development of these devices. We demonstrate that the ion transport through the brushes is governed by the interplay of electrostatic ion–polymer binding and steric effects, leading to a mobility that depends nonmonotonically on grafting density. However, the ion–polymer binding can be modulated by the dielectric properties of the substrate. As a result, surface polarization suppresses ion mobility near insulating interfaces and enhances it near conducting interfaces, even causing a shift from nonmonotonic to monotonic variation with grafting density.

Molecular Dynamics Simulations of Ion-Containing Polymers Using Generic Coarse-Grained Models

“…Using generic CG MD simulations, the Luijten group showed that dielectric mismatch between polyelectrolyte solution and the substrate creates image charges (surface polarization) that have significant impacts on ion mobilities (Figure 7c). 216 Nguyen and Olvera de la Cruz also demonstrated that the chain conformation of polyelectrolytes confined in a spherical cavity is influenced by the dielectric mismatch between the media inside and outside of the cavity. 217 Overall, all the selected works demonstrate the significance of incorporating a more comprehensive description of dielectric mismatch into MD simulations; proper modeling of dielectric mismatch may allow for deeper insights specifically into ion transport or ion distribution in ion-containing polymers.…”

“…(c) Generic CG simulations of polyelectrolyte chains grafted on a substrate and the ion mobilities as a function of graft density for different dielectric substrates. Adapted with permission from ref .…”

“…Ions on each side of the interface respond to electric fields differently, leading to different degrees of polarization and a net surface charge. Using generic CG MD simulations, the Luijten group showed that dielectric mismatch between polyelectrolyte solution and the substrate creates image charges (surface polarization) that have significant impacts on ion mobilities (Figure c) . Nguyen and Olvera de la Cruz also demonstrated that the chain conformation of polyelectrolytes confined in a spherical cavity is influenced by the dielectric mismatch between the media inside and outside of the cavity .…”

Structure of Polyelectrolyte Brushes on Polarizable Substrates

“…We employ the same coarse-grained model as in our recent work on ion transport through PEBs . We model anionic PE oligomers as bead–spring chains , of N = 10 monomers, each carrying an elementary charge − e .…”

HSMA: An O(N) electrostatics package implemented in LAMMPS

“…Furthermore, many materials interfaces are characterized by a discontinuity in the permittivity, resulting in induced surface polarization charges. This induced charge may significantly affect the ionic distributions [21,22,23,24,25,26] and dynamics [27,28,29], so that developing efficient methods for modeling spatially varying dielectrics has received considerable research attention [30,31,32,33,34,35,36]. Whereas this is typically costly, the special situation of planar interfaces (as well as systems that can be approximated as such) can be treated highly efficiently and accurately via the wellknown image-charge method (ICM) [37].…”