Abstract:

Objective Conventional high-performance polymer precursors for laser induced graphene (LIG) strain sensors are often rigid, limiting their use for wearable applications that require high stretchability. Moreover, graphene transferred onto flexible substrates is prone to fracturing or detaching, which degrades sensing performance. In order to address these challenges, this study employed carbonized mesh cotton spunlace nonwoven fabric (CSNF) as a novel precursor to fabricate a high-performance LIG strain sensor.

Method This study involved the carbonization of mesh CSNF, followed by the laser induced synthesis of graphene and the assembly of strain sensors. The microstructure and properties of the resulting graphene were characterized using scanning electron microscopy (SEM), Raman spectroscopy, X-ray diffraction (XRD), and a four-point probe measurement system. The sensing performance, including sensitivity, strain range, response/relaxation time, and stability, was evaluated using a digital multimeter and a universal tensile testing machine.

Results Carbonized cotton spunlace nonwoven fabric (CCSNF) were prepared at different carbonization temperatures and carbonization time periods. The Raman spectroscopy analysis results suggested that the optimal carbonization temperature for CSNF was 600 ℃ and the carbonization time period was 2 h. The precursor (CCSNF-2) prepared under the parameters has a high defect density and disorder degree, providing an ideal basis for the subsequent laser-induced generation of high-performance graphene. The CCSNF was subsequently subjected to laser treatment under optimized parameters. The resulting LIG exhibited optimal electrical conductivity, achieving a square resistance of 37.3 Ω/□ at a laser power of 11.4 W and a scanning speed of 500 mm/s.The LIG was then encapsulated with polydimethylsiloxane (PDMS) elastomer to fabricate flexible strain sensors. The as-fabricated LIG strain sensors demonstrated high performance, including a gauge factor of 612, a low detection limit of 0.5%, a broad strain range of up to 55% strain, rapid response/recovery relaxation characteristics (response time about 0.2 s, time about 0.29 s), and excellent cycling stability (withstanding 1 000 cycles at 20% tensile strain).In order to evaluate practical applicability, the sensors were mounted on various anatomical locations including fingers, wrists, elbows, the throat, and the perioral region. These deployments enabled successful monitoring of human movements through stable and reproducible resistance changes. Furthermore, attachment of the sensor to the metacarpophalangeal joint enabled applications in encrypted information transmission based on gesture recognition.

Conclusion Using mesh CCSNF as a precursor for LIG significantly enhances sensor performance. The unique mesh structure of the fabric contributes to a wide strain range, high sensitivity, and durability. This promising technology has potential applications in emotion recognition, information encryption, sports and rehabilitation monitoring, electronic skin, human-computer interaction, wearable electronics, and healthcare.

Key words: cotton spunlace nonwoven fabric, laser induced graphene, flexible strain sensor, sensing performance, motion monitoring