Microheterogeneity of Calcium Chloride-Based Deep Eutectic Solvents

Area of Science:

• Materials Science
• Physical Chemistry
• Computational Chemistry

Background:

• Metal salt-based deep eutectic solvents (DESs) are increasingly used in applications like electrodeposition and nanoparticle synthesis.
• Calcium chloride hexahydrate is a key component for creating inexpensive, biodegradable DESs with controlled water content.
• Despite practical interest, the microstructure and molecular dynamics of these hydrated DESs remain poorly understood.

Purpose of the Study:

• To investigate the microstructure and molecular dynamics of two specific DESs based on CaCl2·6H2O using molecular dynamics simulations.
• To characterize the phase behavior and interactions within DESs formed with choline chloride (DES1) and ethylene glycol (DES2).

Main Methods:

• Utilized molecular dynamics (MD) simulations with a validated, polarizable force field.
• Developed a new molecular model for ethylene glycol for accurate simulation.
• Analyzed structural properties, phase segregation, and hydrogen bonding networks.

Main Results:

• Both DESs exhibit significant microheterogeneity, with interweaving organic and aqueous phases linked by calcium chloride domains.
• DES1 (choline chloride) shows distinct choline-rich domains within a connected aqueous environment.
• DES2 (ethylene glycol) displays continuous microphases of water and ethylene glycol, with fewer Ca2+·Cl- complexes than DES1.
• A rich hydrogen bond network involving all components was observed in both systems.

Conclusions:

• Molecular dynamics simulations with polarizable force fields are effective for elucidating the microstructure of hydrated metal salt DESs.
• The findings provide detailed molecular-level insights into the structural organization of these complex solvent systems.
• Understanding microstructure is crucial for optimizing DES applications in various chemical processes.