Dynamic Acid/Base Equilibrium in Single Component Switchable Ionic Liquids and Consequences on Viscosity.

Area of Science:

• Chemical Engineering
• Materials Science
• Environmental Science

Background:

• Nonaqueous solvent systems for carbon dioxide (CO2) capture often suffer from high viscosity, limiting their practical application.
• Understanding molecular factors controlling viscosity is crucial for developing efficient CO2 capture technologies.

Purpose of the Study:

• To identify key molecular features governing the bulk viscosity of single-molecule CO2-binding organic liquids.
• To propose a molecular design strategy for reducing viscosity in CO2 capture solvents.

Main Methods:

• Investigated the relationship between molecular structure and bulk viscosity in organic liquids designed for CO2 capture.
• Analyzed the role of hydrogen bonding and proton transfer equilibrium in determining solution viscosity.
• Utilized single-molecule CO2 binding organic liquids as a model system.

Main Results:

• Fast CO2 uptake kinetics are linked to the proximity of alcohol and amine sites, forming a zwitterionic species.
• The population of internal hydrogen bonds significantly influences solution viscosity.
• Viscosity can be controlled by chemically tuning the proton transfer equilibrium towards neutral species.

Conclusions:

• Hydrogen bonding networks, rather than ion pair interactions, are key to viscosity in these novel CO2 capture solvents.
• A molecular design strategy focusing on shifting proton transfer equilibrium can effectively reduce solvent viscosity.
• These design principles are applicable to a broader range of CO2 capture technologies.