Ethanolamine-mediated microstructural transitions within terpenoid- and fatty acid-based deep eutectic solvents

Area of Science:

• Green chemistry
• Materials science
• Physical chemistry

Background:

• Deep eutectic solvents (DESs) are tunable media with unique physicochemical properties.
• Hydrogen bonding extensively influences DES formation and properties.
• Tailoring DES properties is crucial for their application.

Purpose of the Study:

• To investigate the effect of ethanolamine (MEA) addition on the viscosity of DESs.
• To explore the role of fatty acids in MEA-modified DESs.
• To understand the microstructural changes induced by MEA in DESs.

Main Methods:

• Formulation of DESs using terpenes (menthol/thymol) and fatty acids (decanoic acid).
• Addition of ethanolamine (MEA) as a co-solute.
• Characterization using viscosity measurements, density, conductivity, UV-Vis, FTIR, DSC, and fluorescence probes.
• Analysis of Kamlet-Taft parameters.

Main Results:

• MEA addition caused an unprecedented increase in dynamic viscosity for DA-based DESs, while maintaining Newtonian fluid behavior.
• Non-DA based DESs did not exhibit this viscosity increase.
• Microstructural changes were confirmed by various spectroscopic and thermal methods, and fluorescence probes.
• The carboxylic acid group of decanoic acid was identified as critical for the observed changes.

Conclusions:

• The judicious addition of a co-solute like MEA can effectively manipulate DES physicochemical properties.
• Fatty acid functionality is key to inducing microstructural changes and viscosity enhancement in DESs.
• This study provides an efficient strategy for tailoring environmentally benign DES media.