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The implementation of various devices into textiles has attracted a lot of attention and has led to the emergence of the smart textiles field. Most textile fibers are insulating materials, however, conducting fibers are required to develop e-textiles.
A team of Researchers from Europe have now transformed insulating thermoplastic monofilament textile fibers into conducting fibers by coating them with graphene, and opening up a new platform to build integrated electronic devices directly into textiles.
Current interest towards device integration into textiles includes sensors, photodetectors, transistors, electro-luminescent devices, supercapacitors and solar cells. When people think of textiles they automatically think of clothes and garments, however, textiles extends much further than this and could find itself in a wide-range of applications, including in the healthcare, military, fashion, aviation, automotive and transport, construction, geo-textiles and packaging industries.
Most applications of smart textiles will not only involve the mounting of a device onto the textile, but the direct integration of specific functionalities onto textile fibers looks set to revolutionize the field of wearable electronics. The integration approach will allow future textiles to exhibit beneficial properties, such as antibacterial properties, static elimination and electric conductivity.
To realize these e-textiles, conducting fibers are going to be the cornerstone to their success, as they can be used as lightweight, and integrated, wiring for the electronic components. They can also provide a platform for the direct fabrication of electronic devices onto the textile fibers.
Most common conductive fibers in research today rely on a polymer composite, commonly PEDOT:PSS, but now this team of Researchers have decided to coat graphene onto different thermoplastic monofilament fibers. This technique has been tried before, but is limited in the type of polymers tested, but these Researchers have decided to test a wider range of fiber types and of varying sizes.
Unlike many of the other graphene coated fibers, this coating was produced by electrostatic adhesion of graphene at the surface of monofilament fibers, which does not require the impregnation an agglomeration of the fibers. The adhesion of the graphene coating to the textile fibers was found to be strong and durable, and a straightforward coat was achieved by encapsulation with an insulating polymeric layer.
The Researchers used a combination of polypropylene (PP), polylactic acid (PLA) and polyethylene (PE) to fabricate tape-shaped textiles using a monofilament extrusion line. Once formed, an Ultra-Violet Ozone (UVO) treatment (UVO Cleaner® 144AX-220, Jelight Company Inc.) was performed and the samples were then coated with graphene, either monolayer or multi-layer depending on the test, using a cold-wall chemical vapor deposition technique.
The coated fibers were characterized by multiple techniques, including profilometry (Taylor Hobson TalyScan), scanning thermal microscopy (SThM, PARK SYSTEMS XE7), atomic force microscopy (AFM, Veeco/Bruker Dimension 3100), Raman spectroscopy (Renishaw spectrometer), UV-Vis micro-spectrometer (custom built with an Acton SP2500 entrance slit, a PIXIS400 CCD camera and a IntelliCal system- all Princeton Instruments) and scanning electron microscopy (SEM, Hitachi SU-70). Electrical measurements were taken using a Keithley 237 source-measure unit.
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The coated fibers displayed sheet resistance values as low as 600 Ωsq-1, and showed that the high conductivity of graphene was not lost during the transfer to the textile fibers. The fibers also had the ability to withstand up to 1000 bending cycles, down to a bending radius of 5 mm, with no significant change in the resistance. The method is also very versatile and can be applied to different textile fibers, different shapes and sizes and to different types of graphene (smaller cylindrical nylon coated fibers were also tested with similar results).
The coating process provided a high continuity and quality finish across all of the samples, which led to an even and complete covering of the coating, without the need for pre-treatment. The UVO treatment could be used, and was found to improve the conductivity of the coated fibers, and lower the sheet resistance, but sometimes caused damage to the fiber, making them more fragile.
The high conductivity observed in these coated textile fibers make these materials promising candidates for future applications involving conductive textile fibers. The outstanding electrical conductivity and optical transparency makes graphene-coated fibers a candidate for transparent conductors in future smart textile applications.
Sources and Further Reading
- “Towards conductive textiles: coating polymeric fibers with graphene”- Neves A. I. S., Scientific Reports, 2017, DOI:10.1038/s41598-017-04453-7