Ultra-stretchable MWCNT-Ecoflex piezoresistive sensors for human motion detection applications

Ultra-stretchable sensors are highly desirable for wearable electronic applications. In this paper, we manufactured self-standing piezoresistive sensors using a simple method based on blending multiwall carbon nano-tubes (MWCNTs) with a stretchable elastomeric matrix (Ecoflex). The sensors showed a low electrical percolation threshold of 0.3 wt%, with an elastic modulus as soft as the human skin in the forearm and palm dermis. An increase in the cross-linking degree of the matrix from 17.43 +/- 0.20 mol/m(3) up to 28.55 +/- 2.07 mol/m(3) was observed with the incorporation of MWCNTs, revealing that the conductive filler is covalently bonded to the elastomeric matrix. The piezoresistive sensors showed high stretchability with an outstanding linearity between the resistance change with the applied strain, up to 200%, with significant sensitivity which is essential to use these sensors in human motion applications, e.g. forger bending, walking or speaking, and even detecting a hot liquid poured into a cup. Finally, MWCNT-Ecoflex sensors showed remarkable mechanical and electromechanical response features which are essential for wearable applications to monitor human motion with minimal discomfort.