Micellization behavior of morpholinium-based amide-functionalized ionic liquids in aqueous media

Area of Science:

• Physical Chemistry
• Supramolecular Chemistry
• Materials Science

Background:

• Ionic liquids (ILs) are versatile solvents with tunable properties.
• Functionalized ILs offer enhanced performance for specific applications.
• Understanding micellization is crucial for surfactant and IL design.

Purpose of the Study:

• To synthesize and characterize morpholinium-based amide-functionalized ionic liquids (ILs) with varying alkyl chain lengths (n=8, 12, 16).
• To investigate the micellization and adsorption behavior of these ILs in aqueous media.
• To compare their performance against non-functionalized ILs and conventional cationic surfactants.

Main Methods:

• Synthesis and characterization of [C(n)AMorph][Br] ILs.
• Surface tension measurements to determine critical micelle concentration (cmc) and surface tension at cmc (γ(cmc)).
• Conductivity measurements for cmc, degree of counterion binding (β), and standard free energy of micellization (ΔG(m)°).
• Isothermal titration calorimetry (ITC) for micellization thermodynamics.
• Steady-state fluorescence spectroscopy for cmc, micropolarity, and aggregation number (N(agg)).
• Dynamic light scattering (DLS) and atomic force microscopy (AFM) for micelle size and shape.
• 2D (1)H-(1)H nuclear Overhauser effect spectroscopy (NOESY) for micelle structure.

Main Results:

• The synthesized [C(n)AMorph][Br] ILs demonstrated significantly better adsorption and micellization behavior than non-functionalized ILs and conventional surfactants.
• Key performance indicators such as higher adsorption efficiency, lower γ(cmc), and much lower cmc were observed.
• [C16AMorph][Br] exhibited distinct micellization behavior compared to [C8AMorph][Br] and [C12AMorph][Br], corroborated by multiple techniques.
• Thermodynamic and structural insights into micelle formation were obtained.

Conclusions:

• Morpholinium-based amide-functionalized ILs represent a promising class of surfactants with superior performance.
• The alkyl chain length plays a significant role in modulating micellization behavior.
• These functionalized ILs hold potential for applications requiring efficient interfacial activity and self-assembly.