Nanostructuration Effect on the Thermal Behavior of Ionic Liquids

Area of Science:

• Materials Science
• Physical Chemistry
• Chemical Engineering

Background:

• Ionic liquids (ILs) exhibit complex thermal behaviors influenced by molecular structure.
• Understanding the relationship between alkyl chain length and phase transitions in ILs is crucial for their application.

Purpose of the Study:

• To investigate how nanostructuration in imidazolium-based ionic liquids affects their glass and melting transitions.
• To identify the critical alkyl chain size (CAS) where thermal behavior trends shift.

Main Methods:

• Synthesis and characterization of [Cn C1 im][NTf2 ] and [Cn Cn im][NTf2 ] ionic liquid series.
• Differential scanning calorimetry (DSC) to determine glass transition temperature (Tg) and melting temperature (Tm).
• Analysis of the impact of varying alkyl chain lengths on IL thermal properties.

Main Results:

• A trend shift in glass transition temperature (Tg) was observed at the critical alkyl size (CAS) of n=6.
• Above CAS, nanostructuration leads to a plateau in Tg due to intensified van der Waals interactions.
• Melting temperature (Tm) shows a V-shaped profile, influenced by electrostatic interactions and packing ability below CAS, and by nonpolar domain formation above CAS.

Conclusions:

• Nanostructuration significantly governs the glass and melting transitions of ionic liquids.
• The critical alkyl size (CAS) of n=6 marks a transition in how alkyl chains influence IL thermal properties.
• Above CAS, the thermal behavior of ILs resembles alkanes, emphasizing the role of nonpolar alkyl domains.