On the molecular correlations that result in field-dependent conductivities in electrolyte solutions

Abstract

Employing recent advances in response theory and nonequilibrium ensemble reweighting, we study the dynamic and static correlations that give rise to an electric field-dependent ionic conductivity in electrolyte solutions. We consider solutions modeled with both implicit and explicit solvents, with different dielectric properties, and at multiple concentrations. Implicit solvent models at low concentrations and small dielectric constants exhibit strongly field-dependent conductivities. We compare these results to Onsager–Wilson theory of the Wien effect, which provides a qualitatively consistent prediction at low concentrations and high static dielectric constants but is inconsistent away from these regimes. The origin of the discrepancy is found to be increased ion correlations under these conditions. Explicit solvent effects act to suppress nonlinear responses, yielding a weakly field-dependent conductivity over the range of physically realizable field strengths. By decomposing the relevant time correlation functions, we find that the insensitivity of the conductivity to the field results from the persistent frictional forces on the ions from the solvent. Our findings illustrate the utility of nonequilibrium response theory in rationalizing nonlinear transport behavior.

Conductance of concentrated electrolytes: multivalency and the Wien effect

“…The system parameters match the implicit solvent simulation parameters in Ref. [48]: z+ = z− = 1, n salt = 0.1 M, T = 300 K, ε = 10, µ = 3.14 s/Kg and a = r+ + r− = 3.49 Å. The molar conductuvity in our numerical results (Eq.…”

“…Recently, field-dependent ionic conductivities were calculated from molecular dynamics simulations, using generalized fluctuation-dissipation relations [48,49]. This method yields the differential conductivity, κ diff ≡ d J /dE 0 , related to the standard conductivity, κ = J /E 0 , by κ = (1/E 0 ) E0 0 κ diff (E) dE.…”

“…9, the simulation results of Ref. [48] for the molar conductivity are reproduced, where the differential conductivity is converted by integration to the standard conductivity. The simulations take into account the solvent only implicitly and do not account for the conductivity correction due to the counterflow of the solvent.…”

Bridging Database and Experimental Analysis to Reveal Super-hydrodynamic Conductivity Scaling Regimes in Ionic Liquids

“…The NE model, in this form, assumes that ion transport can be characterized by continuum hydrodynamics and that cation mobility and anion mobility are independent. Although ionic liquids do not rigorously meet these assumptions, the NE model is often used to understand conductivity scaling in ionic liquids, showing that many ionic liquids deviate from NE predictions. − …”

Intrinsic Interface Adsorption Drives Selectivity in Atomically Smooth Nanofluidic Channels

“…This framework is general and can be used to understand and engineer other functionality in nanofluidic systems. Employing recent generalizations of response theory, − our approach could be extended outside the regime of linear response to provide insight into performance at high driving strengths and between multiple driving forces.…”