Integrated Resistive-Capacitive Strain Sensors Based on Polymer–Nanoparticle Composites

Stretchable electronics, including bioelectronics, electronic skins, and artificial intelligence devices have attracted widespread attention. Stretchable nanocomposites have generated a great deal of interest from scientists because of their tunable properties. In this paper, stretching-induced conductive-dielectric transformations in nanocomposites are proposed and demonstrated for the first time. The transformations have been made possible with the use of four types of nanocomposites. For nanocomposites composed of polydimethylsiloxane (PDMS) and multiwalled carbon nanotubes (MWNTs, diameters 8–15 nm), the critical weight fraction of MWNTs in the transformation is 8.03%, and the specific tensile strain at the transformation point is 37%. When the applied tensile strain reaches the transformation point, the conductive nanocomposites transform into dielectrics. It has been speculated that electron hopping and tunnel currents become obstructed, and, hence, transformations are triggered. One application of this phenomenon is integrated resistive-capacitive strain sensors, which show potential in e-skin applications. A reusable e-skin switch was tested at a person's knuckle. The performance of the fabricated switch exhibited reversibility and repeatability of the conductive-dielectric transformations. The critical transformation weight fractions and transformation points of the three other nanocomposites were also found, but the matrix was replaced with Eco-flex, and the conductive carriers were silver nanoparticles and carboxyl MWNTs.