Ionogels Containing Ternary Mixtures of Ionic Liquids and Water in One-Pot Synthesized Poly(Acrylamide-co-HEMA) Matrix

Abstract:

Lonogels are a highly attractive class of materials owing to their nonvolatility, ionic conductivity, and electrochemical stability. Direct-ink-writing (DIW) is a powerful method to achieve freeform manufacturing; however, formulating ionogels with both DIW printability and mechanical toughness has been a challenge. Here, we present a one-pot, 3D-printable ionogel that provides high ionic conductivity, DIW printability, and mechanical toughness. The ionogels incorporate a copolymer network made of acrylamide (AAm) and 2-hydroxyethyl methacrylate (HEMA) with a tricomponent solution mixture of water and the 1-butyl-3-methylimidazolium tetrafluoroborate-based based ionic liquids with two anions, [BMIM]BF4 and [BMIM]Cl. Carbopol 940 microgel, a rheology modifier, enables printability. The composition ratio between the solution components impacts ionic conductivity and mechanical properties, which are correlated with the interactions between the anionic and cationic species in the solvent. At optimized solvent compositions, electrochemical impedance spectroscopy shows that the ionogel has an ionic conductivity of up to 4.91 mS cm−1 and is capable of uniaxial stretching up to 400% while supporting a 750 g load with thin thread samples with cross sectional areas of ∼5 mm2. The addition of Carbopol 940 results in a shear-thinning behavior that allows printability. Potential applications include flexible/wearable electronics, energy storage devices, and soft actuators.