E-Textile Enabled by Femtosecond-Laser-Induced Graphene Formation on Kevlar

Personal wearable devices are anticipated to have a pivotal role in advanced healthcare, sports, firefighting, and military contexts in the near future. E-textiles are a promising solution, as they can combine electrical and informative functions, incorporating various sensors, actuators, and energy storage components while maintaining a high degree of flexibility and adaptability. However, existing methods for e-textile production involve weaving conductive fibers and installing functional elements onto conventional textiles, which can be time-consuming, cause gradual wear and tear of conductive yarns, and create challenges in integrating different functional units seamlessly. To meet the growing demand for flexible and timely manufacturing of personalized e-textiles, a simpler design and patterning strategy is essential.<br/>Graphene, with its remarkable electrical conductivity and mechanical and chemical stability, is a promising material for e-textiles. Laser-induced graphene (LIG) synthesis, which uses laser scanning to transform carbon precursors into graphene, has gained attention. Textiles, particularly Kevlar, have emerged as valuable LIG precursor materials. Previous attempts using CO2 lasers to convert Kevlar to LIG resulted in textile damage and limitations in resolution and conductivity. To achieve advanced e-textiles, it's essential to explore direct LIG patterning with improved resolution and minimal ablation, eliminating the need for fiber weaving and preserving high LIG conductivity without degradation concerns.<br/>Textiles can be categorized into nonwoven, knit, and woven types, each with distinct physical properties due to their unique structures. Understanding these structures is crucial for creating high-performance e-textiles. Nonwoven textiles consist of randomly aligned yarns mechanically bonded or adhered together. They have high strength but low stretchability. Knit textiles, made from intersecting yarn loops, are inherently stretchable, resembling a mechanical spring. Woven textiles involve interlacing weft and warp yarns, creating special bending sensing networks when subjected to strain.<br/>In this study, we introduce a straightforward method for creating multi-modal e-textiles. We achieve this by one-step, maskless patterning of LIG using near-infrared ultra-short femtosecond laser pulses on various Kevlar textiles, including nonwoven, knit, and woven varieties. Our approach directly transforms common textiles into e-textiles in a cost-effective and simple manner, without the need for fiber weaving, while preserving their flexibility, adaptability, and air-permeability with minimal ablation. This direct laser writing method is faster, more accessible, and allows for better carbon ratio control compared to conventional techniques like chemical vapor deposition (CVD) and thermal reduction. Nonwoven textiles, with their high mechanical strength and resistance to external strains, are suitable for applications unrelated to mechanical strain, such as energy storage devices and temperature sensors. The supercapacitor demonstrates a specific areal capacitance of 36.17 mF/cm², and the temperature sensor exhibits a thermal coefficient of resistance (TCR) of -0.097% per degree Celsius within the temperature range of 5 to 100 degrees Celsius. The knit structure, known for its wide stretchability, is ideal for creating strain sensors to detect human motion, with a gauge factor (GF) reaching 117.9 within a 0-3% strain range. The woven structure, characterized by a lattice-like network, is suitable for fabricating a bending sensor for voice recognition, with a GF of 230 within a 0-0.5% strain range. These demonstrations underscore the capability of femtosecond pulse lasers for one-step, maskless patterning of high-performance LIG sensors and energy storage devices, paving the way for future wearable multi-modal e-textiles.