Monolayer to Bilayer Structural Transition in Confined Pyrrolidinium-Based Ionic Liquids.
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 confinement. The ionic liquids containing cations with shorter alkyl chain substituents form alternating cation-anion monolayer structures on confinement to a thin film, 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 confined inside the pores of a nanoporous electrode, for example, in devices such as supercapacitors or batteries.
†Department of Chemistry, Physical and Theoretical Chemistry Laboratory, University of Oxford, South Parks Road, Oxford OX1 3QZ, United Kingdom.
Alexander M
AM
Smith
‡Department of Chemistry, Imperial College London, London SW7 2AZ, United Kingdom.
Kevin R J
KR
Lovelock
§Department of Mechanical Engineering and Applied Mechanics, University of Pennsylvania, 220 South 33rd Street, Philadelphia, Pennsylvania 19104, United States.
Nitya Nand
NN
Gosvami
∥School of Chemistry, The University of Nottingham, University Park, Nottingham NG7 2RD, United Kingdom.
Peter
P
Licence
‡Department of Chemistry, Imperial College London, London SW7 2AZ, United Kingdom.
Andrew
A
Dolan
‡Department of Chemistry, Imperial College London, London SW7 2AZ, United Kingdom.
Tom
T
Welton
†Department of Chemistry, Physical and Theoretical Chemistry Laboratory, University of Oxford, South Parks Road, Oxford OX1 3QZ, United Kingdom.
Susan
S
Perkin
confinement; double-layer; ionic liquids; self-assembly; surface forces