Breathable Encapsulated Liquid Metal Foam‐Based Soft Stress Sensor

Abstract

soft electronics based on intrinsically stiff materials (graphene, carbon nanotube, MXene, etc.), soft electronics based on LMs have better deformability, stretchability, and durability. [2] Among LMs-based electronics, LMs-based soft sensors have attracted extensive research attention due to the high consistency and low hysteresis.LMs-based soft stress sensors are typically based on one of two mechanisms: piezoresistive [3] or piezocapacitive. [4] The piezoresistive LMs-based soft stress sensors can be fabricated by three methods: 1) injecting LMs into an elastomer (polydimethylsiloxane, PDMS) channel. [3b,5] 2) mixing LM particles with elastomers (PDMS, Ecoflex, Dragon skin). [6] 3) depositing LMs on a subtract (elastomers or textiles). [7] Applying stress deforms the geometry of the LM conductive paths and changes the resistance, which provides a route to measure stress. The piezocapacitive LMs-based soft stress sensors consist of LM particles dispersed in elastomer to form a dielectric layer prepared by mixing LM and elastomers. [4a,8] The piezocapacitive soft stress sensors achieve high initial capacitance and capacitance variation benefiting from the equipotential characteristic of LM particles. In summary, LMs-based soft stress sensors exhibit the advantages Liquid metal (LM)-based soft and wearable sensors have great potential for applications in human motionmonitoring and human-machine interfaces. To avoid smearing of exposed LM, it is necessary to encapsulate LM with elastomers, which decreases the breathability and results in discomfort and even skin irritation. To solve this problem, this work proposes a breathable encapsulated LM foam (BELMF)-based soft stress sensor. By using two polydimethylsiloxane foam layers, the BELMF-based sensor achieves non-smearing and breathability. Meanwhile, a three-dimensional electrode is designed to implement the electric connection without decreasing breathability. Appling stress to the BELMF-based sensor makes the LM foam collapse and forms new conductive paths, which reduces the resistance of the sensor. The sensitivity of the BELMF-based sensor can reach 1.4 Pa −1 . The mechanisms of the breathable encapsulation and the sensor are investigated through experiments and simulations. In addition, the potential applications of the BELMFbased sensor for monitoring human motion are demonstrated.

Recent Advances in Stretchable and Permeable Electrodes for Epidermal Electronics

“…They have been used to create permeable conductors. [35,48,64,[74][75][76][77][78][79][80] In a typical fabrication process, a liquid metal layer was coated on a soft fiber mat and activated into a porous microstructure under ≈1800% strain (Figure 4a,b). [64] The resulting liquid metal fiber mat exhibits excellent stretchability and steam permeability.…”

Single-Line Multi-Channel Flexible Stress Sensor Arrays

“…Novel materials and structures are the most common approaches to enhance the performance of flexible stress sensors, which are determined by the mechanism [ 49 ]. Piezoresistive [ 50 , 51 , 52 ], capacitive [ 53 , 54 , 55 ], triboelectric [ 56 , 57 ], and piezoelectric [ 58 ] are the four mechanisms for flexible stress sensors, as shown in Figure 2 .…”

3D printed modular piezoionic sensors using dynamic covalent bonds

“…[13][14][15][16] At a minimum, the operational device must be conductive, elastomeric, and maintain functionality after storage under ambient conditions. Traditional sensor materials such as carbon nanotubes, [17][18][19] liquid metals, 8,20,21 or organic field effect transistors (OFET) [22][23][24][25] show great promise, however, when placed inside a soft matrix such as silicone, these conductive elements often limit the amount of deformation the material can withstand. The trade-offs between electronic performance, device shape, and mechanical flexibility also place limitations on the implementation and versatility of these sensors.…”