Direct ink writing of piezoresistive isoprene rubber nanocomposites

Abstract Despite the growing interest in flexible electronics and wearable sensors, research in piezoresistive polymer nanocomposites has stagnated in consideration of the polymer matrices, particularly in additive manufacturing (AM) applications. This research focuses on using a low‐molecular isoprene rubber (IR) as a matrix filled with carbonaceous nanoparticles conductive carbon black (CCB) and carbon nanotubes (CNT) to create piezoresistive sensors printed via direct ink writing (DIW). Using IR as a matrix not only provides an avenue for an alternate sensor matrix, but also offers a distinct advantage for retrofit sensor applications to other diene rubber substrates due to both the feedstock and substrate possessing the same vulcanization mechanism. Thereby, the rheological, mechanical, and piezoresistive properties of the IR nanocomposites are fully investigated, with emphasis on non‐ambient conditions (temperature and durability). In this work it is shown that while CCB exhibits a lower gauge factor (between 1.5 and 8) across all strain rates, strain ranges, and temperatures when compared to CNT compounds (gauge factors between 1.5 and 260), CCB compounds possess better linearity, less temperature deviation, and overall better performance under cyclic loading conditions. This is followed by demonstrations for real‐world applications, including the direct‐to‐product printing of a CCB strain gauge on a chloroprene rubber substrate. Highlights AM via DIW of piezoresistive isoprene sensors filled with conductive CB and multi‐wall carbon nanotubes. Printed samples capable of achieving tensile strength >3.5 MPa. CB sensors showed less sensitivity, but better durability and repeatability compared to carbon nanotube filled sensors. Piezoresistive isoprene strain gauge printed on chloroprene substrate with direct adhesion.