Dynamics of fluorinated imide-based ionic liquids using nuclear magnetic resonance techniques

Area of Science:

• Physical Chemistry
• Materials Science
• Chemical Physics

Background:

• Ionic liquids (ILs) are gaining attention for their unique transport properties.
• Understanding molecular dynamics in ILs is key to unlocking their potential applications.
• Fluorinated imide-based ILs are a class of materials with tunable properties.

Purpose of the Study:

• To investigate the rotational and translational dynamics of fluorinated imide-based ionic liquids.
• To elucidate the influence of anion conformational flexibility, fluorination, and mass on IL molecular dynamics.
• To correlate molecular motion with transport properties in ILs.

Main Methods:

• Fast field cycling relaxometry
• Pulsed field gradient nuclear magnetic resonance (PFG-NMR)
• Study of six 1-butyl-3-methylimidazolium ([BMIM]+) based ionic liquids with modified bis((trifluoromethyl)sulfonyl)imide ([NTf2]-/[TFSI]-) anions at varying temperatures.

Main Results:

• Anion conformational flexibility emerged as the dominant factor influencing both rotational and translational ion dynamics.
• The effects of anion fluorination and mass on molecular motion were secondary.
• Fluorination and mass effects were only significant when anion conformational flexibility remained comparable across different ILs.

Conclusions:

• Conformational flexibility of the anion is the primary determinant of molecular dynamics in these ILs.
• Tailoring anion structure for flexibility is a key strategy for controlling IL behavior.
• This study provides fundamental insights into structure-dynamics relationships in ionic liquids.