A multiscale model for charge inversion in electric double layers

Abstract

Charge inversion is a widely observed phenomenon. It is a result of the rich statistical mechanics of the molecular interactions between ions, solvent, and charged surfaces near electric double layers (EDLs). Electrostatic correlations between ions and hydration interactions between ions and water molecules play a dominant role in determining the distribution of ions in EDLs. Due to highly polar nature of water, near a surface, an inhomogeneous and anisotropic arrangement of water molecules gives rise to pronounced variations in the electrostatic and hydration energies of ions. Classical continuum theories fail to accurately describe electrostatic correlations and molecular effects of water in EDLs. In this work, we present an empirical potential based quasi-continuum theory (EQT) to accurately predict the molecular-level properties of aqueous electrolytes. In EQT, we employ rigorous statistical mechanics tools to incorporate interatomic interactions, long-range electrostatics, correlations, and orientation polarization effects at a continuum-level. Explicit consideration of atomic interactions of water molecules is both theoretically and numerically challenging. We develop a systematic coarse-graining approach to coarse-grain interactions of water molecules and electrolyte ions from a high-resolution atomistic scale to the continuum scale. To demonstrate the ability of EQT to incorporate the water orientation polarization, ion hydration, and electrostatic correlations effects, we simulate confined KCl aqueous electrolyte and show that EQT can accurately predict the distribution of ions in a thin EDL and also predict the complex phenomenon of charge inversion.

Extended coarse-grained dipole model for polar liquids: Application to bulk and confined water

“…In the past few years, EQT has been shown to accurately predict the structure and potential of mean force profiles for confined LJ fluids [46,47], CO2 [48], water [40,41] and electrolytes [30,49]. It has also been used within the classical density functional theory (cDFT) to predict various thermodynamic properties of confined LJ fluids and their mixtures [50][51][52].…”

Effect of charge inversion on nanoconfined flow of multivalent ionic solutions

“…0.6 nm away from the solid surface in accordance with the distance previously reported by Lorenz and Travesset 20 and Mashayak and Aluru. 64 Moreover, we observe an increase in the CI for higher concentrations of the multivalent counter-ions, as depicted in Fig. 2.…”

“…It is worth noting that the global electroneutrality in the channel is enforced by including a higher number of counter-ions in the electrolyte solution to screen the negative surface charge of the channel walls. 12,15,23,63,64 The simulations of the nanoconfined electrolyte solution are conducted in the NVT ensemble at 300 K for 10 ns to ensure proper equilibration of the system. Afterward, production simulations are performed for 10 ns.…”

Rectification of bipolar nanopores in multivalent electrolytes: effect of charge inversion and strong ionic correlations

“…Charge inversion is a key phenomenon that highlights the shortcomings of the mean field treatment of PB-type theories. [53,15,46,8,69,70,9] To summarize, in the ON state, the electrolyte has a high density in the pore, so the dominant effect that originates from larger ionic charges is that cations and anions correlate more strongly. That elevates the concentrations of both ionic species inside the pore that, in turn, results in increased currents.…”

“…While there are a lot of charge inversion studies in the literature both for planar double layers [44,45,13,46,15] and negatively charged pores, [25,47,11,48] studies for the behavior of multivalent ions in bipolar pores are virtually absent. One notable example is the paper of Li et al, [11] where the bipolar charge pattern is created by reversible adsorption of multivalent ions on the wall of a symmetric hourglass nanopore only on one side.…”