Dual Functioning Deep Eutectic Solvents and Imidazolium‐Based Ionic Liquids for Synergistic Toughening of Thermoset System

ABSTRACT A greener strategy for toughening thermoset epoxy resin by the combination of imidazolium based ionic liquid (IL) and a newly synthesized salicylic acid (HBA) and triethylenetetramine (HBD) based deep eutectic solvent (DES) is demonstrated in this work. DES served as both a fracture‐toughening agent and curing activator for IL(1‐butyl‐3‐methylimidazolium chloride, bromide, and 1‐ethyl‐3‐methylimidazolium acetate) cured epoxy systems, outperforming the traditional triethylenetetramine (TETA)‐cured systems. Fourier transform infrared spectroscopy (FTIR) and differential scanning calorimetry (DSC) confirmed a single‐phase curing mechanism, with a 30% increase in glass transition temperature ( T g ), indicating effective curing. Mechanical properties showed marked improvement, with tensile strength increasing by up to 55%, impact strength by 60–235%, and fracture toughness by up to 301%, depending on the type of IL involved. Acetate‐based IL and TETA systems also showed enhanced properties, albeit with slightly lower crosslinking density. Dynamic mechanical analysis (DMA) revealed lower tan delta values, indicative of a flexible network and scanning electron microscopy (SEM) confirmed the brittle‐to‐ductile transition on the fractured surfaces. The results demonstrate the potential of DES as a multifunctional additive, leveraging hydrogen bonding, etherification, and esterification to enhance epoxy performance.