Polymer Nanocomposites Containing Carbon Nanofibers as Soft Printable Sensors Exhibiting Strain‐Reversible Piezoresistivity

Designed as flexible and extendable conductive print media for pervasive computing as strain sensors, nanocomposites composed of a plasticized thermoplastic or a cross-linked elastomer and containing carbon nanofibers at concentrations just above the percolation threshold are observed to exhibit a uniquely strain-reversible piezoresistive response upon application of quasi-static tensile strain. At small strain levels, the electrical resistance of these nanocomposites reduces with increasing strain, indicative of negative piezoresistivity. Beyond a critical strain, however, the resistance reverses and increases with increasing strain, revealing the existence of a negative-to-positive piezoresistivity transition that is fully strain-reversible and repeatable upon strain cycling. These characteristics imply that the nanocomposite morphologies are highly stable with little evidence of mechanical hysteresis. The mechanism underlying this transition is attributed to reorientation of high-aspect-ratio nanofibers (initially homogeneously dispersed) at low strains, followed by separation at high strains. While deposition of these nanocomposites as robust print coatings on textile fabric alters the percolation threshold, strain-reversible piezoresistivity is retained, confirming that they are suitable as printable strain sensors.