Polydopamine/Carbon Black/Carbon Nanofiber/Thermoplastic Polyurethane Composite Nanofiber Strain Sensor with Ultrahigh Loading Rate for Human Activity Monitoring

Developing flexible wearable strain sensors that combine high performance and cost-effectiveness remains a challenge. We proposed the polarity-induced adsorption theory based on the like dissolves like principle, which can dramatically increase the loading rate of carbon nanomaterials on TPU electrospun nanofiber substrates, and constructed flexible PDA/CB/CNF/TPU strain sensors (PCCT) with dual-mode three-dimensional nanobrush-bridging structures of binary carbon-based active filler through the introduction of a binary mixed dispersant system. The trend of similar effects on the loading rate and sheet resistance present for a variety of systems proves the objective existence and applicability of the polarity-induced adsorption theory, and then, the microscopic mechanism of action of the model is analyzed and explained. The optimization scheme summarized on this basis resulted in a PCCT with an ultrahigh carbon nanomaterial loading rate of 59.5% and an ultralow sheet resistance of 68.5 Ω/sq, which enabled the constructed high-density three-dimensional conductive network with synergistic double-bridging structures to demonstrate a full-stretch range of responsiveness (0.12–285%) and high sensitivity (GF = 25.5 (0–100%), 84.3 (100–200%) and 312.4 (200–285%)), realizing the performance enhancement of low-cost devices. Finally, testing of the response to different levels of strain including human joint movements and muscle movements such as blinking proved the practical value and wide range of applications of PCCT in the field of human monitoring.