Shape, Size, and Internal Dynamics of Loosely Bound Colloidlike Ionic Clusters in Ternary Solvent Systems

Abstract

We characterize the influence of preferential solvation on the dynamic self-assembly process between small dianionic salts and a macrocyclic tetraimidazolium molecular box into highly defined, colloidlike ionic clusters in solution, called ionoids. Here, we substitute individual solvents in the established optimal ternary solvent mixture dimethyl sulfoxide (DMSO)/glycerol/water 50:43:7 (v/v/v), namely, DMSO through dimethyl formamide, glycerol through ethylene glycol and water through N-methylpropionamide, and such can characterize the changes in shape and size of the structures of loosely bound ionic clusters induced by the substitution of a specific solvent component. Using dynamic light scattering we associate size, shape, and initial durability of ionic clusters with solvent parameters like dynamic viscosity and relative permittivity to highlight the importance of solvent composition for the build-up of globular ionoids as well as anisotropic ionic clusters. To further analyze the solvation state of our dianionic building unit inside the initial ion cloud state, which later affects the self-assembly process of ionic clusters, we perform continuous wave (CW) electron paramagnetic resonance spectroscopy measurements at X-band (∼9.4 GHz) and Q-band (∼34 GHz) frequencies.