Nano-segregation in ionic liquids: scorpions and vanishing chains

Area of Science:

• Materials Science
• Physical Chemistry
• Computational Chemistry

Background:

• Ionic liquids (ILs) exhibit unique nanostructured properties influenced by alkyl chain length.
• Ether-substituted alkyl chains in ILs can alter their structural organization.

Purpose of the Study:

• To analyze structural differences between 1-alkyl-3-methylimidazolium ([Cnmim][Ntf2]) and ether-substituted ([ (C1OC1)(n/3)mim][Ntf2]) ionic liquids.
• To elucidate the molecular mechanisms behind the suppressed nanostructure in ether-chain ILs.

Main Methods:

• X-ray diffraction was used for initial observation of structural differences.
• Molecular dynamics (MD) simulations with a non-polarizable atomistic force field were employed.
• Analysis focused on the polar and non-polar networks within the ILs.

Main Results:

• Ether-substituted ionic liquids ([ (C1OC1)(n/3)mim][Ntf2]) show a persistent suppression of nanostructure compared to [Cnmim][Ntf2].
• This suppression is attributed to altered non-polar region morphologies, not changes in the polar network.
• Non-polar regions shift from bulky segregated domains to thin enveloping ones.

Conclusions:

• The packing inefficiency of oxygen-substituted alkyl chains, chain kinking, and interactions with cations via ether oxygen lone pairs cause the altered non-polar morphologies.
• These findings explain the loss of nanostructure in ether-chain ILs and offer insights for designing ILs with specific properties.