Molecular Features of Reline and Homologous Deep Eutectic Solvents Contributing to Nonideal Mixing Behavior

Area of Science:

• Physical Chemistry
• Materials Science
• Computational Chemistry

Background:

• Deep eutectic solvents (DES) are tunable materials with applications in various chemical processes.
• Understanding the molecular basis of their nonideal mixing behavior is crucial for optimizing their performance.
• Choline chloride and urea derivatives form a significant class of DES with unique properties.

Purpose of the Study:

• To investigate the molecular mechanisms behind the nonideal mixing of choline chloride-based DES with urea derivatives.
• To identify specific molecular features that influence the activity coefficients and mixing behavior.
• To explore the relationship between chemical structure and nanoscale organization within these solvents.

Main Methods:

• Molecular dynamics (MD) simulations were employed to study DES composed of choline chloride and various urea derivatives.
• Analysis focused on hydrogen bonding networks, anion-cation interactions, and spatial distribution of solvent components.
• Calculations of activity coefficients were used to quantify deviations from ideal mixing.

Main Results:

• In reline (choline chloride:urea, 1:2), urea's hydrogen bond donors effectively solvate chloride anions.
• Methyl substitution on urea shifts anion interactions towards alkyl chains, increasing choline chloride activity coefficients.
• Nanoscale segregation and formation of nonpolar domains are observed upon alkyl group introduction to urea.

Conclusions:

• The nonideal mixing behavior of these DES is strongly influenced by the specific interactions between anions, cations, and the urea derivative structure.
• Alkyl substitutions on urea disrupt the polar network, promoting interactions with nonpolar regions and leading to deviations from ideal behavior.
• The findings provide molecular insights into the design of DES with tailored properties for specific applications.