Electrochemical characterization of viscoelastic solutions of supramolecular polymers in phosphonium-based ionic liquids

• Formation of bis urea supramolecular polymer in an ionic liquid/toluene mixture.
• Measurement of the rate constant for the ferrocene oxidation in this mixture.
• Measurement of the ferrocene diffusivity in this mixture.
• Evidence of viscoelastic character of the solution from the mass transfer rate.
• PF6− more efficient chain stopper than (C2F5)3PF3−.

We have combined electrochemical, rheological and light scattering measurements to investigate the viscoelastic character of solutions of (2,4-bis (2-ethylhexylureido) toluene) (EHUT) in toluene in the presence of two ionic liquids: (trihexyl(tetradecyl) phosphonium hexafluorophosphate “Cyphos 110”) and (tris(pentafluoroethyl) trifluorophosphate “aph4-cph12”) used to substantially increase the solution conductivity required for the electrochemical study.The heterogeneous rate constant k0 of the Fc/Fc+ redox couple, the diffusivity (DFc), and the equivalent capacitance values of the double layer were measured in the presence and in the absence of EHUT. For Cyphos 110, the viscosity of solutions increases in the presence of EHUT, but the diffusion current exhibited no fluctuations. By opposition, for aph4-cph12, strong fluctuations of the diffusion current allowed to assign a viscoelastic character to the solutions when EHUT is added.Rheological and light scattering measurements revealed that the two ionic liquids act as chain stoppers for EHUT supramolecular chains. However, aph4-cph12 maintains the viscoelastic character of the EHUT solution whereas Cyphos 110 destroys the supramolecular structure.