Abstract
Owing to the multi-dimensional complexity of human motions, traditional uniaxial strain sensors lack the accuracy in monitoring dynamic body motions working in different directions, thus multidirectional strain sensors with excellent electromechanical performance are urgently in need. Towards this goal, in this work, a stretchable biaxial strain sensor based on double elastic fabric (DEF) was developed by incorporating carboxylic multi-walled carbon nanotubes(c-MWCNTs) and polypyrrole (PPy) into fabric through simple, scalable soaking and adsorption-oxidizing methods. The fabricated DEF/c-MWCNTs/PPy strain sensor exhibited outstanding anisotropic strain sensing performance, including relatively high sensitivity with the maximum gauge factor (GF) of 5.2, good stretchability of over 80%, fast response time < 100 ms, favorable electromechanical stability, and durability for over 800 stretching–releasing cycles. Moreover, applications of DEF/c-MWCNTs/PPy strain sensor for wearable devices were also reported, which were used for detecting human subtle motions and dynamic large-scale motions. The unconventional applications of DEF/c-MWCNTs/PPy strain sensor were also demonstrated by monitoring complex multi-degrees-of-freedom synovial joint motions of human body, such as neck and shoulder movements, suggesting that such materials showed a great potential to be applied in wearable electronics and personal healthcare monitoring.
Highlights
In recent years, flexible strain sensors have experienced rapid development and achieved a series of progresses in many fields like soft robotics [1], artificial skin [2], human motion detection [3,4], personal health monitoring [5], and human-machine interface [6]
To get better sensitivity and larger workable range, which are the main parameters of the strain sensor, many conductive materials based on semiconductors, nanomaterials, and conductive polymers were used to design strain sensitive sensors, such as ZnO [7,8], ZnSnO3 [9], silver nanowire [10], silver nanoparticles [11], carbon nanotube [12,13], graphene [14,15,16], polypyrrole [17], and polyaniline [18], have been applied and coupled to stretchable substrates
Given the flexibility of double elastic fabric as a substrate, and the use of c-MWCNTs and PPy with relatively low cost, excellent mechanical, electrical, and thermal conductivity properties to function as conductive agents, we developed a stretchable biaxial strain sensor by dip-coating in c-MWCNT dispersions and adsorption-oxidizing pyrrole methods to realize real-time monitoring of complicated human body motions
Summary
Flexible strain sensors have experienced rapid development and achieved a series of progresses in many fields like soft robotics [1], artificial skin [2], human motion detection [3,4], personal health monitoring [5], and human-machine interface [6]. To get better sensitivity and larger workable range, which are the main parameters of the strain sensor, many conductive materials based on semiconductors, nanomaterials, and conductive polymers were used to design strain sensitive sensors, such as ZnO [7,8], ZnSnO3 [9], silver nanowire [10], silver nanoparticles [11], carbon nanotube [12,13], graphene [14,15,16], polypyrrole [17], and polyaniline [18], have been applied and coupled to stretchable substrates. These successfully prepared sensors can respond quickly to a large range of testing strain with high stretchability and sensitivity Examples of such flexible sensors include carbonized silk fabric and cotton fabric [19], conductive film made of graphene and ionic conductor [20], thin slice composed of silver nanoparticles and nanowires [21], and conductive fabrics that are polypyrrole-coated [17]. Our findings will manifest that the DEF/c-MWCNTs/PPy strain sensor has favorable anisotropic sensing property, and demonstrate this functional material as a promising candidate for use in wearable electronics and personal healthcare monitoring
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