Investigation of Structure-Property Relationships in Imidazolium-Based Deep Eutectic Solvent Systems, Polymers, and Their Composites

Author

Anita SapkotaFollow

Abstract

This research focuses on the synthesis, characterization, and property evaluation of novel deep eutectic solvents (DESs) and halometallate ionic liquid (HIL)-based polymers, aiming to develop environmentally benign materials with tunable physicochemical and functional properties. A number of plant-derived phenolic chemicals, including phenol, guaiacol, 4-methoxyphenol, syringol, eugenol, and pyrogallol, were used as hydrogen bond donors (HBDs) and imidazolium bromide ionic liquids (EMImBr and BMImBr) as hydrogen bond acceptors (HBAs) to create a series of DESs. To study hydrogen-bonding interactions and the structural impact of HBD substitution, IL:HBD ratio, and alkyl chain length on bonding strength, the synthesized DESs were examined using FT-IR and ¹H NMR spectroscopy. Red shifts in the O–H stretching region and corresponding downfield or upfield NMR shifts confirmed the formation of strong Br⁻···H–O hydrogen bonds, while computational studies of bond lengths further complemented these findings, confirming hydrogen-bond formation and electron delocalization within the DES network. Furthermore, a comprehensive study was conducted on the physicochemical properties of the DES, encompassing density, viscosity, refractive index, thermal stability, and glass transition temperatures.

A family of solvent-free HIL polymers (C_nVImBr:ZnBr₂, n = 2, 4, 6) as well as their composites with non-polymerizable HILs (C_nMImBr:ZnBr₂), were successfully synthesized with different molar proportions (1:0.1, 1:0.3, 1:0.5). The proton NMR spectroscopy confirmed the coordination of ionic liquid monomers with zinc bromide. The swelling study and miscibility test across the polymer series demonstrated a polarity-dependent trend, which varied with changing carbon atom length, from hydrophilic for C₂ systems, to relatively polar materials for C₄ systems, to hydrophobic for C₆ systems. Swelling decreases with increasing ZnBr₂ content, with looser networks (1:0.1) showing higher uptake and tighter ones (1:0.5) showing minimal swelling. Minor deviations were observed, like the slightly higher swelling of the 1:0.3 composition in chloroform. It was, however, noted that C₆ polymers and composites, which were insoluble in water, had high swelling capacities at low concentrations of zinc bromide. Using E. coli, the preliminary antibacterial test revealed no significant inhibitory activity, indicating that ZnBr₂ in the polymer matrix is not bioavailable in the investigated conditions. In summary, this work illustrates how tailored ionic interactions can be used to create multifunctional, sustainable materials with tunable chemical and physical properties by integrating the design principles of DESs and halometallate ionic polymers.

Year manuscript completed

2025

Year degree awarded

2025

Author's Keywords

Deep Eutectic Solvents, Imidazolium, Halometallate Ionic Liquids, Polymers

Degree Awarded

Master of Science

Department

Chemistry

College/School

Jesse D. Jones College of Science, Engineering and Technology

Dissertation Committee Chair

Sourav Chatterjee

Thesis Advisor

Sourav Chatterjee

Committee Chair

Sourav Chatterjee

Committee Member

Kevin Revell

Committee Member

Jonathan Lyon

Committee Member

Caleb Morris

Document Type

Thesis - Murray State Access only

Recommended Citation

Sapkota, Anita, "Investigation of Structure-Property Relationships in Imidazolium-Based Deep Eutectic Solvent Systems, Polymers, and Their Composites" (2025). Murray State Theses and Dissertations. 422.
https://digitalcommons.murraystate.edu/etd/422