Rate-dependent and self-healing conductive shear stiffening nanocomposite: a novel safe-guarding material with force sensitivity

A novel rate-dependent and self-healing conductive composite with a well-defined shear stiffening (S-ST) effect was facilely fabricated by dispersing multi-walled carbon nanotubes (MWCNTs) into a shear stiffening polymer matrix. The storage modulus (G') of the multi-functional composite automatically increased 4 orders of magnitude when encountering external shear stimuli and the G'(max) was over 1 MPa, demonstrating an obvious shear stiffening effect and good safe-guarding performance. It was found that the electrical conductivity changed accordingly when shear stiffening occurred, therefore it can be applied as a force sensor during the attacking process. The rate-dependent piezoresistance effect of the composite was investigated. In quasi-static compression and high rate impact tests, different force signals can be obtained because of the negative and positive piezoresistivity effect. Self-healing tests indicated that the as-prepared composite can maintain its mechanical and electrical properties after destruction and healing treatments. Owing to the shear stiffening performance, the rate dependent conductive composite could both absorb impact energy and sense the attacking forces. Finally, a mechanism was proposed and it was believed that the glass transition induced by B-O interactions and the changes in the microstructure during the external action can be attributed to the S-ST performance and rate dependent electrical conductivity, respectively.