# Thermodynamic Study of Amine-Based Deep Eutectic Solvents with H2O

## TL;DR

This study explores how water interacts with amine-based deep eutectic solvents, revealing structural changes that could improve their use in CO2 capture.

## Contribution

The paper identifies molecular-level interactions and structural rearrangements in amine-based DES-water mixtures, offering insights for solvent design.

## Key findings

- Density and enthalpy data show nonmonotonic behavior with extrema near xDES ≈ 0.4–0.5.
- Negative excess molar volumes suggest enhanced molecular packing due to DES-H2O interactions.
- Viscosity profiles indicate structural rearrangements and formation of compact microstructures in DES-water mixtures.

## Abstract

The densities and viscosities of ([C
n
mimCl]­[MEA] + H2O) systems (n =
2, 4,
6) were measured over 288.15–323.15 K, and the enthalpies of
mixing were determined at 298.15 and 308.15 K. Density data showed
nonmonotonic composition dependence with extrema near x
DES ≈ 0.4–0.5, and negative excess molar
volumes indicated enhanced molecular packing. Viscosity increased
sharply at low DES content and more gradually toward pure DESs, exhibiting
S-shape deviation profiles that reflect structural rearrangements
in both DES-rich and H2O-rich regions. Negative enthalpies
of mixing confirmed exothermic mixing due to strong DES–H2O interactions, and the data were well correlated by the NRTL
model. The coincidence of extrema in density and enthalpy of mixing,
together with viscosity transitions, suggests the formation of complexes
among the DES constituents and H2O, probably leading to
compact ternary DES-like microstructures. Further comparative analysis
revealed that H2O addition reorganizes the hydrogen-bond
network, forming extensive MEA–H2O associations.
These findings offer molecular-level insights for the rational design
of DES-based solvents for CO2 capture and related separation
processes.