Ionic Liquids with Symmetric Diether Tails: Bulk and Vacuum-Liquid Interfacial Structures

Area of Science:

• Physical Chemistry
• Materials Science
• Supramolecular Chemistry

Background:

• Biphilic ionic liquids with alkyl tails are well-understood.
• The behavior of ionic liquids with non-apolar tails, like ether functionalities, is less clear.
• Understanding interfacial properties is crucial for designing novel ionic liquids.

Purpose of the Study:

• To investigate the structural characteristics of C2OC2OC2-mim+/C2OC2OC2-OSO3- at the bulk and vacuum interface.
• To compare the interfacial behavior of ether-functionalized ionic liquids with alkyl-functionalized ones.
• To elucidate the influence of tail functionality on ionic liquid structure and interface properties.

Main Methods:

• Molecular dynamics simulations were employed to study the structural properties.
• Analysis of ion distribution and orientation at the bulk and vacuum interface.
• Comparison with previously studied isoelectronic C[8]-mim+/C[8]-OSO3- ionic liquids.

Main Results:

• The vacuum interface affects C2OC2OC2-mim+/C2OC2OC2-OSO3- only on the nanometer length scale.
• This contrasts with the long-ranged interface effects observed for C[8]-mim+/C[8]-OSO3-.
• Ether-functionalized ions maintain a tail-outward orientation at the vacuum interface.
• The bulk phase shows a less defined alternation between charged networks and tails, diminishing the first sharp diffraction peak.

Conclusions:

• Ionic liquids with ether functionalities exhibit unique interfacial properties compared to those with alkyl tails.
• The nanometer-scale interface effect suggests potential applications where localized interfacial control is desired.
• The diminished structural alternation in the bulk indicates altered intermolecular interactions due to ether functionalities.