Self-Assembly Versus Surface Charge: Interfacial Response of Ionic Liquids

Abstract

The bulk and surface charge-driven interfacial structuring of two 1-decyl-3-methylimidazolium (C10C1Im) orthoborate ionic liquids (ILs), dispersed at various concentrations in the polar aprotic solvent propylene carbonate (PC), were studied using small angle neutron scattering (SANS) and neutron reflectivity (NR). In the bulk, the larger bis(mandelato)borate anion reduced the self-assembly capabilities of the blend relative to bis(oxalate)borate. At a charged Au electrode interface, a distinct interfacial region was detected in all the IL mixtures studied, which was attributed to two interdigitated bilayers of the cation, containing intercalated anions and solvent, and with bulk IL concentration dependence. Under applied potential, higher concentrations showed clear anion effects on the electro-structuring, whereas dilute solutions were anion independent. The complex bulk and electro-responsive interfacial structuring of such self-assembling IL systems in polar media are pertinent to the application of ILs as designer electrolytes for advanced electrochemical technologies, including next-generation batteries and control over the electrical double layer in capacitors.