Laser-Induced-Graphene Formation on the Kevlar Textiles for Wearable Electronic Devices

Abstract

Wearable electronic devices are being widely employed in various situations, including firefighting, the military, fitness/well-being, and healthcare. One of the promising technology candidates for realizing wearable electronics is constructing conductive electrodes directly onto textiles or fibers. Direct laser writing can support the direct conversion of textiles into electrically conductive Laser-Induced-Graphene (LIG) by irradiating the intense laser beam for converting specified precursor materials into LIG via photothermal reactions; this offers the more flexible design changes with faster manufacturing process. The introduction of ultrafast femtosecond lasers with shorter pulse durations could improve the patterning resolution while minimizing the unexpected material ablation. Kevlar is one of the fabrics having a high melting temperature so fits well for the successful synthesis of LIG using the ultrashort femtosecond laser pulses. We examined the electrical sheet resistance, surface morphology with an SEM, and chemical composition with a micro-optic Raman spectrum. After the characterization, we applied this patterning strategy to realize various wearable electronic sensors (e.g. strain sensors, temperature sensors, bending sensors) and energy storage devices on Kevlar. Textiles are made up of woven, nonwoven, and knit structures, each with its own set of physical properties.<br/>A Yb-doped fiber femtosecond laser, power/polarization control optics, a Galvano scanner, beam-delivery mirrors, and a central control unit make up our direct-laser-writing system. At a 200-kHz repetition rate, the laser generates a repeated pulse train with a 1030-nm wavelength and a 350-fs pulse duration. For patterning of fabric strain sensors and energy storage devices, the laser's average power varied from 0.5 to 3 W while the beam-scanning speed varied from 10 to 30 mm/s. A Galvano scanner angularly scanned the laser beam, which was then focused on target fabrics with an f-theta lens. On-demand, the entire system was concurrently commanded to produce arbitrary patterns. For validating the physical and chemical characterization of LIG, sheet resistance, SEM, XRD, FT-IR, and Raman spectroscopy were conducted. Kevlar to LIG conversion in ambient air was achieved using femtosecond laser direct writing, which may be used in a variety of wearable devices. The resulting LIG is used to construct wearable strain sensors, bending sensors, temperature sensors, and supercapacitors based on the physical characteristics of different fabrics due to its features. The bending sensor is effectively realized for woven cloth. The TCR of the nonwoven temperature sensor is employed for monitoring body temperature, and the capacitance of the nonwoven supercapacitor is 12 mF/cm<sup>2</sup>. The knit strain sensor is well established, and finger movements and human heartbeats were all detected. As a result of the direct conversion of Kevlar to LIG, LIG-based wearable sensors might be used in the military, firefighting, and sports sectors, among other things. Furthermore, we will investigate the possibilities of LIG production with ordinary fabrics, as well as the cleaning challenges associated with textile LIG devices.