The Role of Interfaces in Ionic Liquid‐Based Hybrid Materials (Ionogels) for Sensing and Energy Applications

Abstract

Ionogels have established themselves as an intriguing type of composites, owing to their distinctive properties, including superior thermal stability, non‐flammability, tunable electrochemical stability window, and high ionic conductivity. Hybrid materials based on ionic liquids (ionogels) are held together by interfaces arising out of intermolecular interactions, including electrostatic, van der Waals, solvophobic, steric, and hydrogen bonding. The interfaces within the ionic liquid (ILs) and its multifaceted interplay with the encapsulating matrix greatly influence the physicochemical and electronic/ionic interactions within the composite resulting in exceptional characteristics, allowing for the design of ionogels for targeted applications. Though ionogels have shown superior properties comparable to neat ILs, they still exhibit relatively low mechanical strength, limiting their application in several practical technologies. Simultaneous enhancement of mechanical durability while retaining high ionic conductivity is indispensable, which requires understanding interfaces and related influencing parameters. This review provides a synergetic comprehension, focusing on the interactive forces and factors affecting the conductivity, stability, and robustness of ionogels. Correlating with interfaces, several strategies, including the implications of nanofiller incorporation on the electromechanical properties of ionogel, are also elaborated. Finally, a primer is provided on the application of ionogels in sensors and energy harvesting technologies.

Machine Learning-Enabled Environmentally Adaptable Skin-Electronic Sensor for Human Gesture Recognition

“…Obviously, the concentration of ionic liquid (IL) could have a strong effect on the electrical properties and the mechanical properties as well. 22 Nevertheless, the high content of IL can be the main reason for serious liquid leakage and poor mechanical properties. In this study, the solution containing more than 30% IL failed to cure due to separation during the photocuring process.…”

“…In recent years, there has been a significant increase in the development of stretchable electronic sensors due to the growing demand for wearable applications. − These stretchable sensors can detect and collect physical changes from the various parts of the human body, consequently modulating the mechanical stimuli into electrical signals for monitoring physiological healthcare information. − Viscoelastic polymers, often conformally attached to human skin, have emerged as one of the most promising material choices for such stretchable sensors, arising from their desirable inherent characteristics of flexibility, stretchability, body friendliness, and durability, and have further led to the adoption of various novel materials and device configurations for improved aforementioned performances. − However, many extensive attempts have been made to focus on and improve the stretchability and sensitivity of stretchable sensors, even exhibiting several thousand stretchability and excellent sensitivity. These attempts include multilayered composite stretchable films, nanoparticle-embedded films, microcrack or groove structures, and novel device structural architectures to improve stretchability and sensitivity. − Among the stretchable materials, ionic liquid-based films have attracted much attention owing to their advantageous potential in terms of a wide range of stretchability and recovery as well as optical transparency and biocompatibility. − It is well-known that these ionic liquid-containing polymer films represent an important viscoelastic electronic material in which the conducting ionic liquid molecules embedded in the insulating elastic solid polymer matrix give rise to the conductivity change due to their increased hopping distance when stretched. − …”

Ionogels: recent advances in design, material properties and emerging biomedical applications

“…Generally, piperidinium and pyrrolidiniumbased ILs usually exhibit higher oxidation potentials than imidazolium-based ILs but lower ionic conductivity. 224,245 For instance, solid-state ionogel electrolyte prepared by confining IL [Py 13 ] + [TFSI] À and [Li] + [TFSI] À within sol-gel prepared TiO 2 gelators exhibited high electrochemical stability with the anodic limiting potential reaching about 5 V versus Li/Li + . 246 Another work done by Guo et al 206 demonstrated the ionogel membranes consisting of hydrogen-bonded supramolecular PIL-UPy copolymer networks and [DEIM] + [TFSI] À .…”

An ultra-tough and ultra-sensitive ionogel pressure/temperature sensor enabled by hierarchical design of both materials and devices

“…10,11 Ionogels integrate the advantages of non-volatility, transparency, wide-range operating temperatures, high conductivity and good electrochemical stability, endowing their suitability in pressure sensors. [12][13][14][15][16][17][18][19][20] However, most existing ionogels suffer from low strength and toughness due to the high content of liquids. 21 Increasing the amount of permanent covalent crosslinking sites can readily enhance the mechanical strength but will inevitably lead to high rigidity and non-reversibility.…”