The selective recovery of critical materials, including metals, enables a wide range of important technologies. Owing to its scalability and low input energy requirements, liquid-liquid extraction (LLE) is a predominant method for separations of metals, including rare earth elements, actinides, and platinum group elements. In LLE, amphiphilic extractant molecules bind metals, transferring them from a polar aqueous phase to an immiscible nonpolar organic phase. The distribution of metals between the two phases depends on the difference in solvation free energy between those phases. As the energy difference needed for effective, reversible separations processes can be relatively small, even as small as the thermal energy, a frontier of separations research is understanding the impact of organic phase structure beyond the primary metal coordination sphere. To that end, LLE systems are often modeled as microemulsions, where organic phase structure is treated as colloidal particles representing reverse micellar aggregates. An important limitation of LLE is third phase formation, a liquid-liquid phase transition where, upon sufficient loading of polar solutes into the nonpolar organic phase, it splits into "heavy" and "light" phases. The heavy phase contains most of the extractant molecules and extracted polar species, while the light phase primarily consists of the organic solvent, also called the diluent. The resulting three-phase system is incompatible with processing equipment, resulting in a limit to the per-contact loading capacity of the organic phase.