Effects of dielectric inhomogeneity in polyelectrolyte solutions

Abstract

We illustrate the effects of dielectric inhomogeneity on the statistical Polyelectrolytes in solution form an important class of macromolecules that are essential in biology and colloidal science, and have been the subject of intensive theoretical and experimental investigations; see ref. 1 for an extensive review of the issues and relevant literature.The standard model for polyelectrolytes in solution typically assumes some chain models for the polymer, such as the beadspring model, 2 lattice model 3 or Gaussian thread model, 4 in implicit solvents. The charges are taken to interact with Coulomb potential in a dielectric medium, with a uniform dielectric constant of the solvent. Some studies account for the solvent explicitly by treating the solvent molecules as LennardJones particles, 5 but the electrostatic interactions are still included at the level of dielectric continuum with a uniform dielectric constant. In reality, however, the typically hydrophobic polymer backbone can have a very different dielectric response than the solvent, which will alter the electrostatic interactions between the charges in the vicinity of the polymer. While the use of a uniform dielectric constant of the solvent can be rationalized when the segmental concentration of the polymer is low, as in the case of dilute, good-solvent conditions, it can no longer be justied when the polymer concentration becomes high. The latter can correspond either to a concentrated bulk solution, or to a single polymer in or near a collapsed or partially collapsed state. Even under dilute, goodsolvent conditions, the degree of charge condensation can be affected by the local dielectric response of the polymer backbone. 6In this communication, we demonstrate the importance of including the dielectric inhomogeneity in modeling polyelectrolytes in solution by considering a single polyelectrolyte chain in solvent with no added salt. The decrease of the local dielectric response in the vicinity of the polymer leads to two effects: rst, it alters (strengthens) the Coulomb interactions between the charged species, and second, it expels the counterions from the polymer-rich regions due to the unfavorable solvation energy. The combination of these two effects substantially inuences the chain conformation and degree of charge condensation. For example, we show that upon decreasing the dielectric constant of the polymer backbone from that of the solvent, a collapsed polyelectrolyte chain can turn into the coil state.For computational efficiency, we adopt a lattice formulation by combining the bond uctuation model (BFM), 7,8 a standard lattice Monte Carlo method for polymers, 9 with a local algorithm developed by Maggs et al.10-12 for computing the electrostatic interactions. This algorithm requires a computational effort of order N, 10 and can be directly implemented on a lattice, making it naturally compatible with lattice models of polymers. Furthermore, the dielectric difference between the polymer and the solvent can be easily incorporated. Thus, the la...

Importance of Varying Permittivity on the Conductivity of Polyelectrolyte Solutions

“…In Figure 3 we have also plotted simulation results where there is a sharp dielectric interface (thin green line) at the surface of the polyelectrolyte, with a discrete rise from 2 within the polyelectrolyte to 78.5 in the fluid. As observed in other studies [9,13], the discrete change in the dielectric interface also produces a thickening of the Debye layer. However, the difference in the distribution compared to the Poisson-Boltzmann (thick black line) result is significantly less than in our simulations with a permittivity adapted to the local salt concentration (dotted line).…”

Conformation Change, Tension Propagation and Drift-Diffusion Properties of Polyelectrolyte in Nanopore Translocation

“…The definitions of these quantities are given in Section 4.1. It has been reported that the three quantities have the mean values of about 6.4, 0.45 and 0.57 for neutral chains in bulk solutions [26,45,46], whereas for polyelectrolytes, the values are around 7.1, 0.52 and 0.72, respectively [26,47]. Therefore, charged chains are more elongated or stiff than neutral chains.…”

Dielectric pearl‐necklace model of flexible polyelectrolytes for electrostatic solvation energy calculations

“…Nakamura and Wang have already incorporated the discontinuity of the dielectric medium on a lattice model of partially charged self avoiding walks of N sites, associating different dielectric constant to the links that connect two nearest‐neighbors sites or two monomer sites. Their Monte Carlo simulation of a weakly charged chain in poor solvent (N = 100) demonstrates that the end‐to‐end distance increases from a collapsed state (at ε in = ε w ) to a more expanded conformation when the dielectric constant of the polymer is decreased.…”