Development of a simple, molecular dynamics‐based method to estimate the thickness of electrical double layers

Abstract

Electrical double layers (EDL) exist for all interfaces and determination of EDL thicknesses remains a difficult task. In this study, molecular dynamics (MD) simulations are employed aiming to develop a simple method for effective evaluation of EDL thicknesses. The EDL thicknesses at clay minerals/water interfaces are calculated by MD simulations and empirical Debye lengths, considering different electrolyte solutions (NaCl, KCl, CsCl, PbCl2 and CaCl2), electrolyte concentrations (0∼1.28 mol/L) and charge locations (tetrahedral and octahedral substitutions). Both methods predict the comparable EDL thicknesses at very low concentrations and more EDL compressions at higher concentrations, while MD simulations show the significant improvements in three aspects, as more rational declining trends with increase of concentrations (Critical for estimating EDL thicknesses especially in highly concentrated solutions), inclusion of ion‐specific effects (More EDL compression for divalent than univalent metal ions, and distinct EDL thicknesses for different alkali ions) and reflection of strong dependence on charge locations (EDL thicknesses differ for montmorillonite and beidellite and have a milder declining rate for montmorillonite). Insights are also offered regarding the microstructure of EDLs, and results promote the understanding of EDLs that determine all interfacial properties and processes.

Unraveling the Molecular Interface and Boundary Problems in an Electrical Double Layer and Electroosmotic Flow

“…Therefore, applying a precise boundary at the interface can reduce the deviation between the EDL thickness values obtained using MD simulations and the continuum approach at a high ionic concentration. Gu et al reported that the EDL thickness differs with the ion concentration, and at a higher ionic concentration, the deviation between MD simulation and empirical Debye length is larger than that at a low ionic concentration …”

“…Gu et al reported that the EDL thickness differs with the ion concentration, and at a higher ionic concentration, the deviation between MD simulation and empirical Debye length is larger than that at a low ionic concentration. 73 Effects of Dissimilar Atomistic Boundary and Hydrodynamic Property on Electroosmotic Flow. Figure 8 shows the effect of the dissimilar molecular boundary on the EOF velocity profiles obtained from both MD simulation and continuum perspectives.…”

Continuous-flow macromolecular sieving in slanted nanofilter array: stochastic model and coupling effect of electrostatic and steric hindrance

“…Results of the mPB are qualitatively and quantitatively different from those of the original PB equation, such as a higher electrostatic potential drop across the electrical double layer (EDL) and thicker EDL for larger ions. [46][47][48][49] The counterion used in this study is Tris, whose radius estimated from atom models is approximately 4 Å, 50 larger than that of monovalent cations often used in buffer solutions. 51 Thus, the mPB equation can estimate the Δφ electrostatic potential difference between shallow and deep regions of the SNA more accurately than the original PB equation.…”

Calculation of Shear Layer Thickness of Ionic Rare Earth Particles in Mixture Electrolytes during In-Situ Leaching Process

“…The most famous one, the Gouy-Chapman theory, applied the Poisson-Boltzmann equation to the diffuse double layer and obtained its analytical solution in 1910-1913 [14]. Related research works [15,16] used 1/k to calculate the thickness of the double layer and analyzed the effects of various factors, including concentration and particle shape, on it. Chang et al [17] obtained the influence of electrolyte type and surface charge density on the diffuse layer by solving the Poisson-Boltzmann equation that considers parameters such as ion radius and Minerals 2023, 13, 733 2 of 9 electrolyte concentration.…”