Shape and stiffness memory ionogels with programmable pressure-resistance response

Abstract

Flexible pressure sensors usually require functional materials with both mechanical compliance and appropriate electrical performance. Most sensors based on materials with limited compressibility can hardly balance between high sensitivity and broad pressure range. Here, we prepare a heterophasic ionogel with shape and stiffness memory for adaptive pressure sensors. By combining the microstructure alignment for stiffness changing and shape memory micro-inclusions for stiffness fixing, the heterophasic ionogels reveal tunable compressibility. This controllable pressure-deformation property of the ionogels results in the pressure sensors’ programmable pressure-resistance behavior with tunable pressure ranges, varied detection limits, and good resolution at high pressure. Broad pressure ranges to 220 and 380 kPa, and tunable detection limit from 120 to 330 and 950 Pa are realized by the stiffness memory ionogel sensors. Adaptive detection is also brought out to monitor tiny pressure changes at low stiffness and distinguish different human motions at high stiffness. Using shape and stiffness memory materials in pressure sensors is a general design to achieve programmable performance for more complex application scenarios.

Emerging Iontronic Sensing: Materials, Mechanisms, and Applications

“…Ionic Gels. Considering the water evaporation problem of the hydrogel, ionic gels have emerged as an alternative option for ionic skin and artificial intelligence [70][71][72][73][74][75][76][77]. Ionic gels are typically formed by swelling polymer networks in ionic liquids.…”

Bio-Inspired Ion-Conducting Foam Elastomer for Human Motion Monitoring

“…Ionic conductive elastomers, including hydrogels, ionogels, and liquid-free ionic conductors, have drawn great attention for flexible electronics due to their softness, self-healing, and stretchable properties. − Although great progress in the flexible ionic pressure sensors has been achieved, the sensitivity and detectable range are still the limited factors for their practical applications. To solve the problem, porous ionic conductors, such as gradient ionogels and ionic liquid-doped porous polymers, were prepared for high-performance pressure sensors. , Although these strategies could greatly increase the sensitivity and broad the detection range, the preparation processes of these porous ionic conductors are very complicated. Moreover, the leakage of liquid solvent of the porous ion gel may also limit their practical applications.…”

Humanoid Ionotronic Skin for Smart Object Recognition and Sorting

“…More specifically, the failure strength, Young’s modulus, and toughness of CIIS are 4-fold, 18-fold, and 8-fold higher than those of the hydrated BNC aerogel (Table S1). The advantages of CIIS in terms of the balance between toughness and Young’s modulus, i.e., two of the most important mechanical properties for biomaterials, are also significant even when compared with the previously reported ISs and other commonly used biomaterials such as PAA-ISs, ,,, PAM-ISs, − PVA-ISs, ,, cellulose-ISs, − and SF-ISs. ,− For example, although hydrogel-elastomer hybrid materials have a toughness of up to 41.5 MJ m –3 , their Young’s modulus is only 134 kPa, which is more than 380 times lower than that of CIIS. By contrast, the Young’s modulus of P­(AAm- co -AA) IS can reach 289.7 MPa, while its toughness is only 9.7 KJ m –3 , i.e., 165 times lower than that of CIIS (Table S2).…”

“…In addition to the challenges related to mechanical endurance, another limitation of humanoid ISs is their weak capability for tactile perception. The available tactile object recognition of ISs is mostly based on pressure/force/strain sensing. ,− However, mechanics-based sensing is insufficient for complex object recognition tasks, e.g., intelligent sorting. For example, substances with similar mechanical features, e.g., hard rubber ball and wood ball with similar stiffness, cannot be distinguished by the contact pressure alone.…”