Microphase separation in oil-water mixtures containing hydrophilic and hydrophobic ions

TL;DR

This study introduces a lattice-based Monte Carlo simulation to explore phase behaviors in oil-water mixtures with hydrophilic and hydrophobic ions, revealing complex spatially modulated structures influenced by ion interactions.

Contribution

The paper presents a novel simulation method capable of handling dielectric heterogeneities and uncovers diverse microphase-separated structures driven by ion-mediated interactions.

Findings

Identification of lamellar, tubular, droplet, and gyroid phases

Ion partitioning between water-rich and water-poor regions

Phase behavior tunable via concentration, ionic properties, and temperature

Abstract

We develop a lattice-based Monte Carlo simulation method for charged mixtures capable of treating dielectric heterogeneities. Using this method, we study oil-water mixtures containing an antagonistic salt, with hydrophilic cations and hydrophobic anions. Our simulations reveal several phases with a spatially modulated solvent composition, in which the ions partition between water-rich and water-poor regions according to their affinity. In addition to the recently observed lamellar phase, we find tubular, droplet, and even gyroid phases reminiscent of those found in block copolymers and surfactant systems. Interestingly, these structures stem from ion-mediated interactions, which allows for tuning of the phase behavior via the concentrations, the ionic properties, and the temperature.