Clothing that could harness the kinetic energy of a wearer's movement has been generally considered the realm of sci-fi, but we've never been closer to being able to buy it off store shelves.
A team of researchers from the University of Massachusetts Amherst has found a way to apply a layer of conducting polymer known as Poly(3,4-ethylenedioxythiophene) (or PEDOT for short) to plain fabrics, also allowing them to retain their functionality under stress such as stretching, washing, and ironing.
The conductive material works by using the process of triboelectric charging. This is essentially a process that generates electricity by using the frictional contact between two different materials. Most everyday static electricity is generated from triboelectric charging. It's also been researched as a source of power for wearable devices.
Gif courtesy of Electro Static Technology
The current technology behind most body-mounted devices involves ultra-thin strips of plastic substrates woven into a structure that approximates fabric. Or, in the case of designer fabrics, strips are coated in an active material layer then coated in a polymer cladding before being woven. While this technology is capable of providing some wearable smart properties, it lacks in aesthetics and normally cannot survive the stress and wear of normal clothing.
“The intrinsic breathability and feel of fabrics cannot be replicated by devices built on plastic substrates or cladded designer ﬁbers, no matter how thin or ﬂexible these device arrays are,” said Lushuai Zhang and Trisha Andrew, researchers and authors of a paper published earlier this month in the Advanced Functional Material’s online journal.
The paper described how they coated the conducting surface onto fabric using a method known as chemical vapor deposition. The coating applied was extremely thin, with the thickest coating measuring in at about 500 nanometers, allowing the fabric to retain a normal feeling.
A graphical representation of the chemical vapor deposition process. Image courtesy of MIT News.
Improvements on Previous Attempts
There have been similar attempts at coating familiar fabrics before. But, as the research team points out, “the solution processing methods used to coat these fabrics often resulted in either troubling device variations or in devices that could not be skin-mountable and laundered."
By using vapor deposition to apply an ultrathin coating to the fabric, the researchers are able to primarily keep the original mechanical properties of the substrate instead of the coating.
The research team ran tests on 14 different fabrics electrodes and reported unique findings. The fabrics were able to undergo mechanical deformations, laundering, and ironing while maintaining stable conductivity while maintaining the feel and appearance of a standard fabric. The restivities were reported linear, meaning that the length of the fabric wouldn’t disallow its integration into smaller garment designs.
Most fascinatingly, the fabric's electrical properties can be tuned by how it is weaved, without having to adjust processing conditions or chemical composition.
Examples of different weaves demonstrated by the researchers. Image courtesy of the University of Massachusetts Amherst.
Trisha Andrew is also the director of wearable electronics at the Center for Health Monitoring at the Institute of Applied Life Sciences. After her research work at the University of Massachusetts was completed, her lab created a wearable heart rate monitor with a fitness bra with eight electrodes. The bra will be tested in culmination with leggings that have four electrodes to see if the technology is capable of contesting the 12 electrode hospital equipment.
In the future, Andrew and Zhang will be working on turning essentially any garment into a solar cell. They also believe their coating technique to make use of surface grafting, however, this has yet to be fully explored.