Temperature Effects in Adsorption of a Primitive Model Electrolyte in Disordered Quenched Media:  Predictions of the Replica OZ/HNC Approximation

Abstract

A theoretical study of a quenched−annealed system where both components were modeled as charge symmetric +1:−1 primitive model electrolytes is presented. The adsorbed model electrolyte, mimicking lithium chloride solution, was assumed to be in thermodynamic equilibrium with an external reservoir of the same electrolyte. This partly quenched system was studied by applying the replica Ornstein−Zernike (ROZ) integral equation in the hypernetted chain (HNC) approximation and the grand canonical Monte Carlo technique. The effects of the concentration of matrix ions, pre-quenching conditions, and the electrolyte and solvent conditions on the adsorption of electrolyte were examined. The results indicate that the mean activity coefficient of the adsorbed electrolyte may differ substantially from the value of the corresponding quantity in the equilibrium bulk solution. The concentration of the annealed electrolyte in the matrix can be higher (sorption) or lower (rejection) than the corresponding equilibrium bulk concentration, depending on conditions of matrix preparation and on the temperature of adsorption. An important observation of this study is that the ROZ/HNC approximation can be solved for very high couplings, i.e., we can obtain valid results in the region of parameters where the regular OZ/HNC, applied to the equivalent bulk electrolyte solution, fails to converge. The agreement between the computer simulations and ROZ/HNC results for the adsorption isotherms is good.

Electrolyte Exclusion from Charged Adsorbent: Replica Ornstein−Zernike Theory and Simulations

“…The scheme was developed and already applied successfully in the cases where the matrix and the annealed fluid were both electroneutral. [18][19][20][21][22][23][24] The same scheme was applied for the present system, and the corresponding renormalized functions were obtained.…”

“…16 The model studied here differs from those presented before. [18][19][20][21][22][23][24][25] We assume again that the distribution of "frozen" charges corresponds to an equilibrium distribution of ions in an electrolyte solution with dielectric constant and temperature T 0 . However, in contrast to the previous studies, we assume that only anions are "frozen" (quenched) and the cations are allowed to equilibrate.…”

Chemical potential of a hard sphere fluid adsorbed in model disordered polydisperse matrices

“…The approaches based on Eqs. (11) and (17) are expected to perform much better for fluids with long-range interaction; see, e.g., [34,35] for explicit proof of this statement. Having this in mind, we show only the results of PY theory together with Monte Carlo data for the case of very dense polydisperse matrices in Fig.…”

“…Then the concept of affinity of fluid species to matrix medium in addition to the concept of porosity considered in the present work could be discussed (see, e.g., [35]). It is important to mention that for such models the affinity/porosity would depend on the adsorbent preparation conditions, e.g., on the temperature at which the matrix has been formed, as well as on the conditions at which an imaginary adsorption experiment is performed.…”

“…It has been extended to partly quenched fluids and then used to describe the activity coefficients of electrolyte solutions in charged matrices [34,35]. The expression for the excess chemical potential of fluid species generalized here to a polydisperse system reads …”