How Dimethyl Sulfoxide Disrupts the Hydrogen Bond Network in Hydroxy-Functionalized Ionic Liquids

Area of Science:

• Physical Chemistry
• Materials Science
• Computational Chemistry

Background:

• Ionic liquids (ILs) with hydroxyl functional groups exhibit complex hydrogen bond (HB) networks.
• Understanding these networks is crucial for designing ILs with tailored properties.
• Dimethyl sulfoxide (DMSO) is investigated as a hydrogen bond catching agent to modify IL behavior.

Purpose of the Study:

• To investigate the influence of DMSO on the HB network of a hydroxy-functionalized ionic liquid.
• To quantify the thermodynamic stability and kinetics of different HB species.
• To correlate HB network changes with the viscosity of the IL-DMSO mixture.

Main Methods:

• Molecular dynamics (MD) simulations were employed.
• Analysis of hydrogen bond populations and their thermodynamic stability using van 't Hoff analysis.
• Investigation of HB kinetics using HB population correlation functions.

Main Results:

• Three characteristic HBs were identified: cation-anion (c-a), cation-cation (c-c), and cation-DMSO (c-m).
• DMSO addition significantly disrupts the native IL HB network.
• Stable cation-DMSO HBs facilitate DMSO dispersion at low concentrations, while DMSO-DMSO contacts compete.
• Cation-anion HBs are generally weakest; cation-DMSO HBs are stronger than cation-cation HBs.
• HB kinetics correlate well with viscosity, which decreases significantly upon DMSO addition.

Conclusions:

• DMSO acts as an effective HB catching agent, altering the IL's HB network structure.
• The observed changes in HB network and kinetics explain the significant decrease in viscosity.
• Simulation results show good agreement with available experimental data, validating the approach.