Recent advances in liquid mixtures in electric fields

Jumping In and Out of the Phase Diagram Using Electric Fields: Time Scale for Remixing of Polystyrene/Poly(vinyl methyl ether) Blends

We demonstrate it is possible to repeatedly jump polystyrene (PS)/poly(vinyl methyl ether) (PVME) blends from the one-phase to two-phase region by simply turning on and off an electric field at a fixed temperature near the phase boundary. This builds on our previous work that established electric fields enhance the miscibility of PS/PVME blends by shifting the phase separation temperature T_S(E) of 50/50 blends up by 13.5 ± 1.4 K when field strengths of E = 1.7 × 10⁷ V/m are applied (J. Chem. Phys. 2014, 141, 134908). Monitoring the early stages of phase separation and remixing by fluorescence, we measure the remixing time scale τ(T) with and without electric fields, finding τ(T) is unchanged by the presence of the field and well fit by a Vogel-Fulcher-Tammann expression. These observations are consistent with a mobility-limited process several degrees from the phase boundary where electric fields have shifted the miscibility transition.

Electric Double Layer Composed of an Antagonistic Salt in an Aqueous Mixture: Local Charge Separation and Surface Phase Transition

We examine an electric double layer containing an antagonistic salt in an aqueous mixture, where the cations are small and hydrophilic but the anions are large and hydrophobic. In this situation, a strong coupling arises between the charge density and the solvent composition. As a result, the anions are trapped in an oil-rich adsorption layer on a hydrophobic wall. We then vary the surface charge density σ on the wall. For σ>0 the anions remain accumulated, but for σ<0 the cations are attracted to the wall with increasing |σ|. Furthermore, the electric potential drop Ψ(σ) is nonmonotonic when the solvent interaction parameter χ(T) exceeds a critical value χ_{c} determined by the composition and the ion density in the bulk. This leads to a first-order phase transition between two kinds of electric double layers with different σ and common Ψ. In equilibrium such two-layer regions can coexist. The steric effect due to finite ion sizes is crucial in these phenomena.