Transparent, mechanically robust, and ultrastable ionogels enabled by hydrogen bonding between elastomers and ionic liquids

Abstract

A general strategy for the fabrication of mechanically robust ionogels by hydrogen bonding between elastomers and [NTf2]-based ILs is demonstrated.

Conductive and Tough Smart Poly(N‐isopropylacrylamide) Hydrogels Hybridized by Green Deep Eutectic Solvent

“…The Fourier transform infrared (FTIR) spectra of OH characteristic absorption presented a slight red shift from 3460 cm −1 of the pure AA to 3315 cm −1 of DES, which could well prove the formation of intermolecular hydrogen bonds between ChCl and AA inside DES (Figure 1b). As another powerful evidence of hydrogen bonds, the 1 H NMR spectra of pure AA and DES [ 22 ] also displayed the integral movement to the lower field, which was attributed to the enhancement of the deshielding effect caused by the decrease of H electron cloud density (Figure 1c and Figure S1, Supporting Information). On account of abundant hydrogen bonds, the AA/ChCl‐based DES could generate the compact interaction with NIPAM as well as the filled water during the copolymerization of monomers and the gelation of hydrogel.…”

A Mechanically Robust and Versatile Liquid‐Free Ionic Conductive Elastomer

“…[ 25 ] Strategies such as fabricating conductive nanochannels and employing ILs that can form hydrogen bonds with polymer chains have been proposed to prevent the loss of ILs. [ 25,26 ] Meanwhile, the tradeoff between ionic conductivity and mechanical robustness should be addressed as well—in general, using a large amount of ILs can enhance the conductivity of gels but cause degradation of mechanical properties (e.g., strength and modulus). [ 3,22,25 ] More recently, ionotronic diodes and transistors have been demonstrated with the use of ionic conductive elastomers that are comprised entirely of polymer networks and mobile ions and contain no liquid components, such that these devices are non‐volatile without the hassles of leaking liquid materials.…”

“…At the molecular scale, dense arrays of hydrogen bonds form between the anions and copolymer network, with the hydrogen atoms in the P(MEA‐ co ‐IBA) chains acting as hydrogen bond donors and the electronegative atoms (such as F and N) in the TFSI anions serving as the acceptors. [ 26 ] In addition, a large number of lithium bonds formed between lithium cations and carbonyl oxygens on polymer chains are confimed by attenuated total reflectance Fourier transform infrared spectroscopy (Figure S10, Supporting Information). Lithium bonds are much stronger than hydrogen bonds.…”

Advances in Materials for Soft Stretchable Conductors and Their Behavior under Mechanical Deformation

“…Ionic conductors are not confined to hydrogels and can also be formed as ionogels—ionic liquid-based gel systems—and also elastomers that include ions or ionic liquids. Ionogels are a new class of soft materials with ionic conductivity and thermal stability, and unlike most hydrogels, do not dry out in open air, offering a promising option for soft stretchable conductors [ 13 , 120 , 128 , 129 , 130 , 131 , 132 ]. Figure 5 depicts examples of transparent ionogels ( Figure 5 a,b) along with a representative demonstration of mechanical strain ( Figure 5 b).…”

“… ( a ) Schematic description of a transparent, mechanically robust, and stable ionogel enabled by hydrogen bonding. Reproduced with permission from [ 128 ]. Copyright 2020, Royal Society of Chemistry ( b ) Mechanical characterization of a 3D printed crosslinked ionogel.…”