Electrically conductive yet insulating aramid nanofiber Janus films via gel–gel assembling for flexible motion sensing and Joule heating

The growing high demand for electronic sensors with both wearability and multi-functional integration has attracted tremendous attention in the field of flexible electronic devices like artificial intelligence and human–computer interaction. The nanocomposites with the Janus structure are being developed into the new generation sensor applied in flexible wearable electronic devices. Herein, boron nitride nanosheets (BNNS) and carbon nanotubes (CNT) were introduced to the aramid nanofibers (ANF) matrix and prepared to gels, respectively. The (B/A)-(C/A) (BNNS/ANF-CNT/ANF) Janus film that contains BNNS/ANF layer and CNT/ANF layer was further fabricated via a vacuum-assisted filtration method. A robust and steady interfacial adhesion was achieved based on a unique gel-gel assembling. It was found that the mechanical, conductive and thermal management properties of the entire Janus film were affected by the synergies between BNNS and CNT with different content combinations. The (30B/A)-(40C/A) Janus film (30 wt% BNNS and 40 wt% CNT) integrated the properties of high mechanical strength (86.8 MPa), electrical insulation (88.6 kV/m), conductive (221.4 S·m−1) and good through-plane thermal transmission (0.42 W/(m·K)) was used as a sensor for motion monitoring, showing good stability and reliability (1000 cycles). Additionally, the Janus film exhibited good Joule heating performance. Overall, the prepared (B/A)-(C/A) Janus film showed promising prospects in lightweight, flexible and multifunctional electronics.