Facile preparation of stretchable and multifunctional ionic gels via frontal polymerization of polymerizable ternary deep eutectic monomers with a long pot life

The weak or brittle mechanical properties, icing and water evaporation under very low or high temperatures, the complex preparation process and high costs limited the application of ionic hydrogels and ionogels. Here, we designed and prepared stretchable and multifunctional ionic gels via frontal polymerization (FP) of polymerizable ternary deep eutectic monomers (DEMs) with a long pot life. The highly stretchable ionic gels can be obtained by altering the molar ratio of polymerizable and non-polymerizable hydrogen bond donors (HBDs), acrylamide (AM) and urea (U), together with hydrogen bond acceptor (HBA), choline chloride (ChCl), respectively. FTIR and 1 H-NMR spectra were used to characterize the chemical structure of DEM. Preliminary experiment indicated the pot lives of ternary DEM were much longer than that of the corresponding binary DEM without U. The obtained DEMs were investigated for preparing multifunctional ionic gels by FP. As the molar ratio of U to M changed from 0.7:1.3 to 1.3:0.7, the tensile and compressive strength of ionic gel decreased from 225 KPa and 3129 KPa to 24.7 KPa and 210 KPa, respectively. However, the elongation at break of the ionic gel increased from 283% to 680%. After FP, the DES composed of U and ChCl embedded in the cross-linked PAM not only acted as a plasticizer, but also as a conductive and anti-freezing agent of ionic gels. This work provides a rapid, green and low energy consumption method to construct stretchable, conductive, self-healing and anti-freezing ionic gels, which can be used in flexible bio-electronic devices in the future.