Aggregation behavior of sodium dioctyl sulfosuccinate in water-contained choline chloride-ethylene glycol deep eutectic solvent and its effects on electrochemical behavior of copper ions

Deep eutectic solvents (DESs) are attractive due to their advantages as solvents and electrolytes. Self-aggregation of surfactants would affect physico-chemical properties of DESs and thus electrochemical behavior of electroactive species in DESs. Aggregation behavior of sodium dioctyl sulfosuccinate (AOT) in choline chloride-ethylene glycol mixture containing 4 wt.% water (ethaline-4% H2O) was evaluated by surface-tension measurement. And surfactant effects on electrochemical behavior of copper ions in ethaline-4% H2O electrolyte were investigated by viscosity and ionic conductivity measurements, electrochemical experiments, and morphology analysis. The results show that critical micelle concentration value is 5.32 mM, and viscosity of ethaline-4% H2O increases upon increase of AOT concentration, while ionic conductivity decreases. Two redox couples relating to Cu(II)/Cu(I) and Cu(I)/Cu(0) from cyclic voltammograms were observed at both GCE and Pt electrodes. Using cyclic voltammograms of copper ions at Pt, diffusion coefficients and rate constants of Cu(II) were calculated and found to decrease when AOT concentration increases from 0 to 20 mM. Nucleation and growth processes are fitted well with instantaneous nucleation mode regardless of AOT concentrations from chronoamperometric data of Cu(I)/Cu(0) at GCE. Furthermore, scanning electronic microscopy analysis indicates that aggregation of surfactant AOT near critical micelle concentration plays important role in copper morphology control.

Automated summary

This study evaluated the aggregation behavior of a surfactant in deep eutectic solvents (DESs) and its effects on the electrochemical behavior of copper ions. The results showed that increasing the concentration of the surfactant led to an increase in the viscosity of the DES and a decrease in its ionic conductivity. The rate of the oxidation-reduction reactions of copper ions was also influenced by the surfactant concentration. Additionally, the aggregation of the surfactant near the critical micelle concentration played an important role in controlling the morphology of copper.