Multifunctional Flexible Ionic Skin with Dual-Modal Output Based on Fibrous Structure

Abstract

Flexible wearable electronic devices with multiple sensing functions that simulate human skin in all aspects have become a popular research topic. However, the current expensive and time-consuming means of integration and the complex decoupling process are hampering the further development of multifunctional sensors. Here, an ultraflexible ionic fiber membrane (IFM) prepared by a simple electrospinning technique is reported, which exhibits pressure and humidity sensing properties. With the help of different electrode structures, the IFM-based multifunctional sensor achieved pressure and humidity detection with different sensing mechanisms. Pressure sensing with high sensitivity (49.7 kPa–1 at 0–30 kPa) and wide detection range (0–220 kPa) was indicated by the capacitive signal. Humidity sensing with high linearity (1.086% per percent relative humidity (RH)) in the range 15%–90% RH was indicated by the resistance signal. In particular, the multimodal output of capacitance/resistance corresponding to pressure/humidity in this study directly addresses the problem of accurately distinguishing the two stimuli. Furthermore, we have demonstrated that the impact between pressure and humidity is negligible when measured simultaneously and independently. Because of the excellent pressure/humidity sensing performance, we have fabricated a smart bracelet and mask for pulse, skin moisture, and breathe monitoring, which indicates the promising future of multifunctional flexible sensors based on IFM in the healthcare field.

Facilely Prepared Reprocessable High-Performance Polyurea Ionic Conductive Elastomers Based on HUBs with Strain- and Temperature-Sensing Capability

“…The sample can achieve complete stress relaxation within 2000 s at 140 °C, which means that the dynamic urea bonds in the cross-linked network of the HUBTPU IL20 are sufficiently activated at this temperature so that the cross-linked network exhibits dynamic characteristics. We calculated the activation energy of dynamic urea bonds using the Arrhenius equation, and the result is shown in Figure b, and the activation energy Ea decreased from 109.66 kJ/mol of HUBTPU to 91.18 kJ/mol . We speculate that the decrease in activation energy may be due to the doping of ionic liquids reducing the T g of the hard segments.…”

“…We calculated the activation energy of dynamic urea bonds using the Arrhenius equation, and the result is shown in Figure 4b, and the activation energy Ea decreased from 109.66 kJ/mol of HUBTPU to 91.18 kJ/ mol. 32 We speculate that the decrease in activation energy may be due to the doping of ionic liquids reducing the T g of the hard segments. It facilitates the movement of the chain segments in which the HUBs are located, allowing the HUBs to dissociate more rapidly at the molecular level, thus promoting the stress relaxation of the material.…”

“…Polyurethane is a typical block polymer consisting of soft segments with low glass transition temperature and rigid hard segments; − at room temperature, the soft segments are free to move and can build channels for ionic motion, thus enabling the transfer of electric current; meanwhile, the rigid hard segments endow the material with excellent mechanical properties. Therefore, in recent years, a great deal of research has reported ICEs based on polyurethane/polyurea elastomers. ,,− Zhao et al recently constructed a novel ICE based on waterborne polyurethane, introducing carboxylic acids into the hard segment, constructing a hard segment region with regular arrangement of hydrogen bonding to form an efficient ion conductive channel, which effectively improves the electrical conductivity. However, the linear structure restricts the strength of the materials, which is no longer suitable for application scenarios where high strength is required .…”

Research Progress and Application of Multimodal Flexible Sensors for Electronic Skin

“…It can be seen from the above that under the identical active material, the signal interference problem of the dual-mode sensor can be solved by the design of the structure. For example, Zhou et al 98 prepared force-humidity dual-modal sensors with different sensing mechanisms by using different electrode structures to realize different output signals when detecting force and humidity. As depicted in Figure 3B, the IFM is positioned between two PI/Au electrodes to create a sandwich structure for a flexible capacitive pressure sensor.…”

Self-Perceptional Soft Robotics by a Dielectric Elastomer

“…Inspired by biology, a large number of precontact sensing techniques have been investigated in soft robots, such as ultrasonic sensing, , infrared sensing, optical sensing, − biosensing, laser sensing, magnetic sensing, , and capacitive sensing. , Among these techniques, capacitive sensing in soft robotics has some significant advantages. It owns the advantages of simple structure, high sensitivity, flexible design, low detection limit, wide application range, and endurability, which have been widely studied in pressure sensing, − strain sensing, , and noncontact sensing. , This makes capacitive sensing a promising approach to soft robot perception.…”