Abstract:

Objective Smart textiles are a new type of textile material that highly integrates flexible electronic devices with fabrics, which has great application potential in medical health and sports monitoring. The fabrication of flexible piezoresistive sensors, which enable the interaction between the human body and external information, is crucial for achieving smartness in textiles. Addressing the challenges posed by the intricate preparation process of flexible piezoresistive sensors and the integration of conductive materials with fabrics, this study presents a fabric-based approach to overcome these limitations.

Method Polydimethylsiloxane-multi-walled carbon nanotubes/carbon black (PDMS-MWCNTs/CB) was used as a conductive composite material for coating non-woven fabric, aiming to fabricate a piezoresistive layer. Microdrop injection technique was utilized to pattern fork-finger metal electrodes directly on the fabric surface, thereby facilitating the construction of flexible piezoresistive sensors based on fabric. Characterization and analysis of the fabric metal electrodes, conductive composites, piezoresistive layers, and sensors were carried out using an RTS-4 four-probe tester, field-emission scanning electron microscope, tensiometer, digital bridge, and a self-assembled cyclic recirculation device.

Results Conductive composites with different mass ratios of CB and MWCNTs were prepared, and the piezoresistive properties of the conductive composites with varying ratios of mass were investigated. The results showed that the resistance increment (R₀-R) of conductive composites tended to increase and then decrease with the increase of CB content under the same pressure. When the mass ratio was 3∶2, the conductive composites exhibited superior piezoresistive response characteristics. Conductive composites and pressure-sensitive layers, incorporating MWCNTs with varying filling contents, were fabricated and investigated. The study encompassed morphological examination of the conductive composites and microstructural analysis of the pressure-sensitive layers. The findings revealed that MWCNTs could be uniformly dispersed within PDMS, with a denser conductive network emerging as the filling quality increased. A synergistic conductive network, characterized by a "grape cluster"-like arrangement, was observed to interconnect MWCNTs and CB within the conductive network. The conductive composite material was uniformly deposited on both the surface and within the nonwoven fabric. Flexibility tests demonstrated that the conductive composite material could be securely adhered to the fabric, with no separation of the conductive material from the nonwoven base. Sensitivity quantifies the ability of the sensor to reflect external stimuli accurately. Sensors with varying MWCNT fillings were prepared and tested to assess sensitivity. The results revealed that the resistance change rate escalated with increasing pressure. The sensor exhibited its highest sensitivity of 0.353 kPa^-1 when the MWCNT filling mass fraction reached 2.5%. The comprehensive performance of the sensor was examined, focusing on aspects such as hysteresis, response/recovery time, repeatability stability, and resolution. The sensor, filled with 2.5% MWCNTs, demonstrated a hysteresis rate of approximately 31.2%, attributed to the inherent structure of the nonwoven material. Its response/recovery time was 150/200 ms, with a minimum detection limit of approximately 49 Pa and excellent repeatability stability (about 1 600 times). Furthermore, the responsiveness of the sensor to human motion signals, including pressure signals from finger presses and finger/wrist flexion, was tested. The results indicated that the sensor could detect and provide feedback on finger pressure, finger bending angle, and continuous wrist bending signals, rendering it suitable for applications in human health and motion signal monitoring.

Conclusion This research addresses the difficulty in achieving efficient integration between conductive materials and textiles. The textile-based flexible piezoresistive pressure sensors demonstrate superior sensing capabilities, rendering them appropriate for monitoring human motion signals. These sensors exhibit considerable potential for further development in applications related to human health and movement tracking. Enhanced sensing performance can be achieved by optimizing conductive composite preparation techniques and developing flexible sensors. This sensor may be further enhanced by exploring and incorporating additional fabric substrates.

Key words: flexible pressure sensor, cotton fabric, nonwoven, conductive composite material, coating method, silver electrode