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

Abstract

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 k 0 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.

Structural, Viscoelastic, and Electrochemical Characteristics of Self-Assembled Amphiphilic Comblike Copolymers in Aqueous Solutions

“…More recently, some supramolecular polymers based on self-assembled bis-urea in apolar solvents exhibited a viscoelastic behavior. − They correlatively displayed most of the features previously reported on subjecting them to the flow of a rotating disk, that is, deviation of the mass-transfer rate from Newtonian behavior for a critical angular velocity and the presence of instabilities …”

“…21−25 They correlatively displayed most of the features previously reported on subjecting them to the flow of a rotating disk, that is, deviation of the mass-transfer rate from Newtonian behavior for a critical angular velocity and the presence of instabilities. 26 It must be emphasized that all of these compounds that display such viscoelastic properties in laminar flow also present the ability to reduce the friction in turbulent flow (so-called drag-reduction phenomenon) viz. linear high-molecular-weight polymers, 27,28 surfactants, 29−34 or even supramolecular polymers.…”