Flexible circuits, environmental and healthcare monitoring, and energy conversion are only a few of the many applications that could be realized by wearable, textiles-based electronics. Researchers at the Cambridge Graphene Centre (CGC) at the University of Cambridge have recently developed a new method that can be used to produce conductive cotton fabrics using graphene-based inks. The method eliminates expensive and toxic processing steps previously required, and opens up new possibilities for flexible and wearable electronics.
The CGC team worked in collaboration with scientists at Jiangnan University, China. In an article published in the journal Carbon, the team demonstrates a wearable motion sensor based on the conductive cotton that was created by depositing graphene-based inks onto cotton to produce a conductive textile.
Cotton fabric is comfortable to wear and breathable, as well as being durable to washing. It is therefore no wonder it is among the most widely used in clothing and textiles. These properties also make it an outstanding choice for textile electronics. Dr Felice Torrisi at the CGC and his collaborators have developed a new process that is a sustainable, low-cost and environmentally friendly method for producing conductive cotton textiles by saturating them with a graphene based conductive ink.
The new method is based on Dr Torrisi’s work on the formulation of printable graphene inks for flexible electronics. The team created inks of chemically modified graphene flakes that adhere to cotton fibers better than graphene that has not been modified. The conductivity of the modified graphene is improved by heat treatment after depositing the ink on the fabric. The adhesion of the modified graphene to the cotton fiber can be compared to to the way cotton holds colored dyes. The fabric also remains conductive after several washes.
Numerous wearable sensors have been developed by researchers around the world. Most of the current wearable technologies however rely on stiff electronic components mounted on supple materials such as textiles or plastic films. In many cases, these are damaged when washed, offer limited compatibility with the skin and, as they are not breathable, are uncomfortable to wear.
Torrisi explained that other conductive inks are not sustainable and very expensive to produce as they are made from precious metals such as silver. On the other hand, graphene is chemically compatible with cotton while at the same time environmentally friendly and cheap.
Professor Chaoxia Wang of Jiangnan University, co-author of the paper, adds that this is an unbelievable enabling technology for smart textiles, as the method will allow electronic systems to be put directly into clothes.
The work done by Prof Wang and Dr Torrisi, together with students Jiesheng Ren and Tian Carey will enable a number of commercial opportunities for graphene-based inks. Possible applications range from high performance sportswear, personal health technology, wearable technology and computing, military garments and fashion.
Dr Torrisi also noted that thank to nanotechnology, clothes could incorporate these textile-based electronics and become interactive in the future. Transforming cotton fibers into functional electronic components will likely open the way to an entirely new set of applications from the Internet of Things, to healthcare and wellbeing.
As graphene is carbon in the form of single-atom-thick membranes, it is highly conductive. The team’s work is based on spreading of tiny graphene sheets in a water-based dispersion. Each sheet is less than one nanometer thick. The graphene sheets in suspension are chemically altered to adhere to the cotton fibers during deposition on the fabric and printing. This leads to a uniform, thin conducting network of many graphene sheets. The secret to the high sensitivity to strain induced by motion is this network of nanometer flakes. A simple graphene coated smart cotton textile deployed as a wearable strain sensor can detect up to 500 motion cycles reliably, even after it has been washed more than 10 times in a normal washing machine.
GRMs and graphene are changing the technology and science landscapes due to their attractive physical properties for sensing, electronics, catalysis, photonics and energy storage. Graphene’s atomic thickness and exceptional mechanical and electrical properties give huge advantages. It allows the depositing of extremely thin, flexible and conductive films on surfaces and on textiles. When these characteristics are combined with the fact that graphene is environmentally compatible and has a strong adhesion to cotton, it make the graphene cotton strain sensor ideal for wearable applications.