Self-aggregation of sodium dodecyl sulfate within (choline chloride + urea) deep eutectic solvent

Area of Science:

• Green chemistry
• Supramolecular chemistry
• Materials science

Background:

• Deep eutectic solvents (DESs) are gaining traction as environmentally friendly alternatives due to their low toxicity and cost.
• Choline chloride-based DESs, like Reline (choline chloride:urea, 1:2 molar ratio), are easily prepared and inexpensive.
• Understanding molecular aggregation in DESs is crucial for optimizing their applications and overcoming limitations.

Purpose of the Study:

• To investigate the self-aggregation behavior of sodium dodecyl sulfate (SDS), an anionic surfactant, within a DES environment.
• To explore the impact of SDS aggregation on the solubility of organic solvents in DESs.
• To characterize the formed aggregates and their potential as nanoreactors.

Main Methods:

• Fluorescence probe experiments, electrical conductivity, and surface tension measurements.
• Dynamic light scattering (DLS) and small-angle X-ray scattering (SAXS).
• Density, dynamic viscosity, and fluorescence probes (pyrene, 1,3-bis(1-pyrenyl)propane) for characterizing aggregates.

Main Results:

• Evidence of sodium dodecyl sulfate (SDS) self-aggregation in the Reline DES, forming well-defined assemblies.
• Significant enhancement in the solubility of organic solvents, such as cyclohexane, within SDS-added Reline.
• Formation of water-free cyclohexane-in-DES microemulsions attributed to SDS aggregation.

Conclusions:

• SDS spontaneously forms aggregates in DESs, leading to the creation of novel oil-in-DES microemulsions.
• These microemulsions exhibit enhanced solubility for immiscible organic solvents.
• The characterized nanoreactor-sized microemulsions offer potential for new chemical applications.