Planetary centrifugal mixing for robust, ultrahighly sensitive sensors with positive piezoresistive effect across an exceptionally broad pressure range based on polyurethane/carbon black composite foam

The pursuit of high sensitivity across a broad measurement range has been a significant and intriguing subject in developing piezoresistive sensors. However, it is important to acknowledge that high sensitivity often comes at the cost of sacrificing the measurement (pressure or strain) range due to the negative piezoresistive coefficient. In this study, a robust piezoresistive sensor based on aqueous polyurethane (APU)/conductive carbon black (CCB) composite foam was fabricated through a planetary centrifugal mixing (PCM) strategy. Under the dual action of high centrifugal and tangential forces in PCM, nano-scaled dispersion of CCB particles and resulting conductive network were embedded within the foam skeleton, combined with a unique thick-wall pore structure through the high viscosity APU/CCB blending during the foaming process. This robust sensor exhibited a distinctive positive piezoresistive behavior. It demonstrated impressively high sensitivity (gauge factor up to 211 at strain over 35 %) across an exceptionally broad pressure range (0.5 kPa-2.84 MPa), far exceeding previously reported piezoresistive sensors. Good durability and reproducibility were also testified over 2000 compression cycles, even at high pressures of 500 kPa,1000 kPa and 1500 kPa after an initial stabilization process. The sensor can monitor diverse stimuli and give stable real-time feedback, ranging from low-pressure fingertip bending to extremely high-pressure vehicle rolling. Without the need for complex preparation processes or expensive materials, the developed strategy opens up an attractive pathway for designing advanced piezoresistive sensors with high sensitivity across a broad measurement range.