Abstract:

Objective Most of the smart wearable products are used as accessories, which limits their application and popularity. In this study, cotton fabrics were used as the substrate, modified by silane coupling agent KH-560, and reduced graphene oxide (rGO) and copper nanoparticles (CuNPs) were used as conductive materials to engineer rGO/CuNPs/cotton fabric(CF) flexible sensors with both conductivity and wearing comfort by impregnation method and in-situ reduction method.

Method The microscopic morphology and elemental distribution of the sample were observed using scanning electron micro-scope (SEM), X-ray energy dispersive spectroscopy (EDS), and transmission electron microscope (TEM). The surface elements and compounds of the samples were analyzed by X-ray photoelectron spectro-scopy(XPS). The surface functional groups of the sample were tested by Fourier transform infrared spectro-scopy(FT-IR). Raman spectroscopy was used to analyze the degree of defects and carbonization of conductive materials. The modified fabric was evaluated using an electronic testing equipment for the resistance changes of the fabric when stretched at different rates and different strains. Cyclic stability and maximum tensile sensing range of the fabric sensor were analyzed. The fabric sensors were fixed at joints, the resistance changes were recorded during motion to explore the sensing and motion-monitoring capabilities.

Results The XPS spectrum of rGO/CuNPs/CF and the XPS spectra of C1s, Cu2p and O1s were analyzed, and the results showed that the GO nanosheets coated on the surface of cotton fabrics were converted into rGO during the reduction process, and the surface defects were reduced, turning Cu²⁺ to Cu⁺. The FT-IR of CF and rGO/CuNPs/CF results showed that the oxygen-containing groups of the fabric decreased or even disappeared after the reduction, further indicating the reduction of GO. The Raman spectra of GO/CF, rGO/CF and rGO/CuNPs/CF results indicated that the supported CuNPs could have a synergistic effect with graphene, and the metal particles were dispersed between the graphene sheets, filling the structural defects on the surface of graphene, preventing graphene agglomeration, and helping to form a complete and continuous conductive network. The tensile resistance of the sensor was tested at strains of 5%, 10% and 15%, tensile rates of 10, 20, 30 and 50 mm/min, and with 6 cycles and 100 cycles. The test results showed that the range of fabric resistance increases with the increase of strain, and the response time becomes faster with the increase of tensile speed, and the resistance of the fabric does not change significantly after 100 stretching cycles. The results also showed that the resistance resumed to the vicinity of the initial resistance value after the external force was removed. The prepared rGO/CuNPs/CF flexible cotton fabric sensors were attached to human joints to test the resistance changes of the conductive fabrics during movement, and the results illustrated that the range of resistance change of the fabric sensors increased with the increase of action amplitude, suggesting that the rGO/CuNPs/CF flexible sensor can be used to perceive the movement behavior of the human body, and can intuitively distinguish the frequency and amplitude of human movement.

Conclusion rGO and CuNPs are loaded onto cotton fabric via the impregnation method and in-situ reduction method, and the rGO/CuNPs/CF conductive fabric with strain-sensing performance is successfully fabricated. The rGO/CuNPs/CF flexible sensor possesses good washing resistance, and exhibits excellent responsiveness as well as cyclic stability when subjected to external tensile force. It can perform the monitoring of human joint movements, and is expected to be applied in fields such as motion tracking, health monitoring, and smart clothing. This study provides a reference for the development of flexible sensors with simple and economical processes as well as excellent performance, and broadens the application scope of flexible conductive cotton fabrics.

Key words: cotton fabric, reduced graphene oxide, copper nanoparticle, sensor, conductive fabric, smart textiles, flexible strain sensor, sensing performance