Ultrahigh Sensitive Carbon‐Based Conducting Rubbers for Flexible and Wearable Human–Machine Intelligence Sensing

Abstract

polymeric elastomers are promising materials for the flexible and wearable applications. These conducting elastomers possess an acquiescent nature with human skin that undergoes mechanical deformation while performing physical actions such as stretching, bending, twiddling, and folding. [4,5] The sensitivity over such mechanical strain has been measured by the performance metric like gauge factor (GF) and calculated by measuring the change in resistance (δR) to the external strain (δε). Achieving the high-performing, flexible, and wearable strain sensors by silicon and metal-based systems are ambiguous due to its low GF. [6] It leads to the use of polymeric elastomers to fabricate strain sensors that can mount directly on human skin to sense signals corresponding to human bodily motions. In line with this, numerous materials and methodologies have been reported in developing high-performing strain sensors. The library of conducting filler materials like carbon black, [7,8] CNTs, [9,10] nanoparticles, [11] nanotubes, [12,13] graphene, [14-17] conducting polymers, [18] and hydrogels [19-21] has been used to fabricate strain sensors. Also, the fabrication methods like photolithography, [22] screen printing, [23] inkjet printing, [24,25] and spray coating [26] are employed to develop strain sensors. Though these strain sensors have demonstrated superior performance than that of metal and silicon-based strain gauges, the extension of lab-scale technology to the commercial use is hitherto unrealized due to the complicated pre-treatments, instability, and inadequate sensitivity. More importantly, the realization of a highly conductive and stretchable platform to transduce both the low-and high-strain functions of the human body remains challenging. It means the sensor component must be highly sensitive to detect the subtle involuntary functions such as heartbeat, breathing, and voice recognition that produce ultra-low strains. Contrastingly, the same sensor components should work under high-strain voluntary functions of the human body. To detect these arrays of functions, developing the ideal material/component with a high and broad range of gauge factor (GF) is essential. In general, The wearable strain sensors with multifunctional applications can fuel the rapid development of human-machine intelligence for various sectors like healthcare, soft robotics, and Internet of Things applications. However, achieving the low-cost and mass production of wearable sensors with ultrahigh performance remains challenging. Herein, a simple, cost-effective, and scalable methodology to fabricate the flexible and highly sensitive strain sensors using carbon black and latex rubbers (LR) is presented. The LR-based strain sensor demonstrates excellent flexibility, fast response (≈600 ms), ultra-high sensitivity (maximum gauge factor of 1.2 × 10 4 at 250% strain), and long-term stability over 1000 cycles. The LR-based strain sensors are sensitive to monitor subtle human motions such as heart pulse rate and voice recognition along with high...

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