Dynamics of Binary Mixtures with Ions: Dynamic Structure Factor and Mesophase Formation

TL;DR

This paper develops dynamic equations for polar binary mixtures with ions, analyzing their structure factor and mesophase formation, revealing microphase separation and mesophase structures influenced by ion solvation and electric effects.

Contribution

It introduces a theoretical framework for ion-influenced dynamics in binary mixtures and demonstrates mesophase formation through simulations, highlighting the role of solvation asymmetry.

Findings

Microphase separation occurs with large solvation asymmetry.

Mesophases exhibit a sharp peak in structure factor at intermediate wave numbers.

Surface tension diminishes in mesophases with increased quench depth due to electric double layers.

Abstract

Dynamic equations are presented for polar binary mixtures containing ions in the presence of the preferential solvation. In one-phase states, we calculate the dynamic structure factor of the composition accounting for the ion motions. Microphase separation can take place for sufficiently large solvation asymmetry of the cations and the anions. We show two-dimensional simulation results of the mesophase formation with an antagonistic salt, where the cations are hydrophilic and the anions are hydrophobic. The structure factor S(q) in the resultant mesophase has a sharp peak at an intermediate wave number on the order of the Debye-Huckel wave number. As the quench depth is increased, the surface tension nearly vanishes in mesophases due to an electric double layer.