Electrical, Mechanical, and Electromechanical Properties of Screen-Printed Piezoresistive Polydimethylsiloxane with Multiwalled Carbon Nanotube Nanocomposites

Polydimethylsiloxane (PDMS) with multiwalled carbon nanotubes (MWCNT) fillers is a piezoresistive nanocomposite which is conformable, printable, and biocompatible. It is widely employed as a sensing layer in flexible pressure sensors, electronic skin (e-skin) of humanoid robots and as wearable sensors. Piezoresistive nanocomposites show significant increase in their electrical conductivity above a certain percolation threshold. In this work, PDMS + MWCNT-based sensing layers with different nanofiller MWCNT concentrations (2, 4 and 7 wt.%) are screen-printed and their electrical, mechanical, and percolation threshold responses are verified. The static I-V characteristics of the samples for a biasing DC voltage of 0-6 V are studied. The tensile test confirms maximum elongation of more than 50 mm. The change in resistance was minimal for 2 wt.% sample as the MWCNT's are sparsely distributed and no conducting channels are formed; for the 7 wt.% sensing layer, negligible change in resistance was observed as the conducting channels are broken. The highest change in resistance of 2.4 M ohm was observed after the percolation threshold value of 4 wt.% of the nanofiller concentration was reached. Overall, the 4 wt.% screen-printed piezoresistive nanocomposite layer showed highest sensitivity with a gauge factor of 4.76 and a linear response suitable for industrial applications.