Monolayer to Bilayer Structural Transition in Con?ned Pyrrolidinium- Based Ionic Liquids

摘要

Ionic liquids can be intricately nanostructured in the bulk and at interfaces resulting from a delicate interplay between interionic and surface forces. Here we report the structuring of a series of dialkylpyrrolidinium-based ionic liquids induced by con?nement. The ionic liquids containing cations with shorter alkyl chain substituents form alternating cation-anion monolayer structures on con?nement to a thin ?lm, whereas a cation with a longer alkyl chain substituent leads to bilayer formation. The crossover from monolayer to bilayer structure occurs between chain lengths of n = 8 and 10 for these pyrrolidinium-based ionic liquids. The bilayer structure for n = 10 involves full interdigitation of the alkyl chains; this is in contrast with previous observations for imidazolium-based ionic liquids. The results are pertinent to these liquids' application as electrolytes, where the electrolyte is con?ned inside the pores of a nanoporous electrode, for example, in devices such as supercapacitors or batteries.