Physico-chemical properties and nanoscale morphology in N-alkyl-N-methylmorpholinium dicyanamide room temperature ionic liquids

Abstract

A series of new room temperature ionic liquids based on N-alkyl-N-methylmorpholinium cations (the alkyl chain ranging from ethyl to nonyl) and a hydrophilic anion (dicyanamide), a mostly unexplored class of room temperature ionic liquids (RTILs), has been synthesized and characterized. Selected physico-chemical properties (density, viscosity and ionic conductivity) have been measured and the salts' propensity to organize into ionic clusters has been explored. The inspection of their Walden plots and electrospray ionization spectra strongly prompts for the occurrence of clustering phenomena, especially for salts bearing long alkyl chains. This structural organization has been confirmed using X-ray scattering techniques and the existence of a high degree of intermediate range order has been detected, as fingerprinted by distinct diffraction features at low Q. These evidences are rationalized in terms of a structural model where, similarly to other RTILs, the alkyl chains tend to segregate from the charged moieties.