Enhanced Interface Bonding of Segregated Conductive Elastomeric Foams by Dynamic Cross-Linking Reshuffling: Toward Highly Sensitive Piezoresistive Sensors

Conductive polymer composites with a segregated structure have been developed for flexible piezoresistive sensors, but segregated composites usually suffer from the problem of poor interfacial bonding. In this work, ethylene-vinyl acetate copolymer (EVA)/carbon nanotube (CNT)/hydroxylated carbon nanotube (CNT-OH) composites with segregated structures were prepared by ball-milled coating and the following hot-press molding, in which dynamic boron-centered three-dimensional cross-linking networks were constructed in EVA granules. The interfacial bonding was significantly improved by molecular bridges at the interface based on thermo-activated transesterification between CNT-OH and EVA vitrimer granules. As a result, the composites with the ratio of CNT to CNT-OH of 3:1 showed a superior elongation-at-break of 563.69%, strength of 12.6 MPa, and conductivity of 13.6 S/m. Furthermore, a 3D porous structure was constructed in the EVA composites by supercritical carbon dioxide foaming. Benefiting from the segregated conductive structure and strong interfacial bonding, the segregated conductive EVA foams exhibited an excellent piezoresistive sensing sensitivity with a GF of −23.6 and compression stability. It provided an approach for interface strengthening of segregated conductive polymer composites, and the resulting conductive foams exhibited great potential for the application as a flexible piezoresistive sensor.