Ultra‐Stretchable, Adhesive, and Anti‐Swelling Ionogel Based on Fluorine‐Rich Ionic Liquid for Underwater Reliable Sensor

Abstract

ideal ionic conductors for flexible electronics because of their high stretchability, transparency, and excellent ionic conductivity. [2] However, ascribed to the introduction of hydrophilic groups, the hydrogel swelling is unavoidable and has become the major technical bottleneck of underwater sensing. Many efforts have been made to address the issue of hydrogel swelling, such as solvent exchange, [3] multiple crosslinking, [4] and supramolecular strategy. [5] For instance, Cui et al. [6] established a type of hydrogels enabled a process of self-hydrophobization produced by Fe 3+ that endow the hydrogels excellent underwater adhesion and stability. Zhao et al. [7] constructed double network hydrogel consisting of poly (acrylamideco-acrylic acid) and sodium alginate with extremely high crosslinking density, which exhibited excellent swelling-resistance underwater. Although these specially created anti-swelling hydrogels can be submerged in water for a period of time, it is still extremely difficult to prevent the ion dispersion due to the concentration gradient, which will severely depress or even completely eliminate their conducting and sensing capacities.Moreover, for consistent and steady signals, the sensor must be securely adhered to the target substrates with a high signalto-noise ratio when utilized underwater. However, achieving strong underwater adhesion remains a challenge for commercial electrodes. [8] The adhesion strength of the substrate will be greatly decreased or even eliminated because water molecules will create a hydration layer on its surface, preventing direct Creating flexible materials that can work underwater has the potential to broaden applications to aquatic and marine environments. Hydrogels have long been thought to be excellent ionic conductors for wearable electronics, because of their high stretchability, transparency, and excellent ionic conductivity. However, due to the huge differences between the underwater and air environments, the previously reported soft materials can rarely satisfy the critical needs of adhesive, underwater stability, and steady conductivity. Herein, an ionogel is proposed with abundant physical and chemical crosslinked, involving ion-dipole, electrostatic, and hydrogen bonding interactions, to achieve excellent mechanical strength, resilience, and underwater stability. The ionogel with long-lasting underwater adherence and durability is further assembled into a high sensitivity, fast response, and excellent durability underwater wearable sensor. The ionogel sensor demonstrated high precision in various human motion detection and Morse code is used to transmit information both in the air and underwater. In addition, the tough underwater adhesion and the distinct discrepancy in electrical properties in different concentration solutions enable the ionogel sensor to adhere to the surface of marine animals and monitor the water quality in their habitats. It is identified that the designed ionogel possesses great promise in wearable devices and soft ionotronics.

A Low‐Hysteresis and Highly Stretchable Ionogel Enabled by Well Dispersed Slidable Cross‐Linker for Rapid Human‐Machine Interaction

“…As indicated, the low-hysteresis property and ionic conductivity of EA-PR-IL-100% stand out compared with similar gel systems. [26,[56][57][58][59][60][61][62][63][64][65] Subsequently, to figure out the resistance change of the ionogel during stretching process, the resistance test during stretching process was implemented. As indicated in Figure 4b, the relative change of resistance was almost linear with the tensile strain and the GF (gauge factor) was ≈0.5, indicating that the ionogel can be deemed as a desirable candidate for strain sensing materials.…”

Underwater Self-Healing and Recyclable Ionogel Sensor for Physiological Signal Monitoring

“…As shown in Figure a and Movie S1, the ionogel could quickly and firmly adhere to a variety of substrate surfaces underwater, such as wood, iron, rubber, polypropylene (PP), glass, and Teflon. It is known that, in the aquatic environment, a hydrated layer can develop at the interface of an adhesive material and the substrate, which reduces the adhesion strength drastically. , In contrast, the hydration layer can hardly be formed between the substrate and hydrophobic ionogel, which is intrinsically water-repelling, while diverse interactions are established between different substrates and the ionogel, such as ion–dipole, dipole–dipole, metal complexation, electrostatic, cation−Π interactions, and van der Waals interactions (Figure b). To characterize the adhesion force, the lap shear test was performed (Figure c).…”

Organohydrogel Strain Sensors with Low Mechanical Hysteresis and Adhesion for High‐Quality Signals

“…[15] Zhao et al reported an adhesive ionogel-based strain sensor for underwater communication. [16] Bai's group has demonstrated the adhesive, biocompatible, and breathable organohydrogel-based strain sensor. [17] Despite these reports having emphasized that the low mechanical hysteresis and adhesion are essential for outputting high-quality signals, the relationship between the intrinsic mechanical properties of material and sensing performance isn't clearly clarified, especially relying on the control samples.…”