|Photo by Priscilla Du Preez on Unsplash|
Thankfully, scientists are people too, and the comfort requirement hasn’t been lost on them. In a recent paper published in the journal Matter, a team of researchers from the University of Windsor (UWindsor) in Canada debuted a new approach to creating textiles that are smart and stretchable, soft, and wearable.
Electronics are traditionally rigid and hard. Fabrics are traditionally flexible and soft. Electronics have smooth metallic surface. Fabrics are composed of twisting, looping fibers that embrace empty space. One of the key challenges to achieving smart materials is seamlessly integrating electronic components, like light emitting devices, and fabrics.
Most existing “light up” apparel is created by sewing rigid electronic components into garments. This works, but it’s a clunky approach that decreases stretchiness and wearability. Flexible electronics, made on thin films, offer a different approach, but require a flat, smooth surface. A more integrated approach is to weave light emitting fibers into woven fabrics, but this technique isn’t compatible with knit fabrics, which are more stretchable.
Led by researcher Tricia Breen Carmichael and Yunyun Wu, one of Carmichael’s PhD students, the UWindsor team took a completely different approach—they turned a soft, wearable, material into a light emitting device. Rather than fighting the open structure of knit fabrics, the team used it to their advantage.
These photographs show the new light-emitting textiles displaying the ‘smiling face’ emoji, a rectangular spiral, and the number 8. Credit: The Carmichael Lab.
A quick note here. Fabrics are classified as woven or knit. Woven fabrics are made by interlacing different fibers at right angles to one another. Knit fabrics are made by forming one long fiber into interconnected loops. As a result of their looping structure, knit fabrics have more stretch. Most lounge clothing (leggings, t-shirts, sweatshirts, etc.) are made of knit fabrics.
You can think of a basic light emitting device as a peanut butter sandwich. The two pieces of “bread” are electrical conductors (electrodes) and the star ingredient that goes between them is a light-emitting (emissive) material. When connected to a power source, the electrodes send current through the emissive layer, which is so-named because it converts some of that electrical energy into emissions—in this case, visible light.
The team realized that if you cover an emissive layer with sheer fabric, the light is still visible. If you cover a stretchy emissive layer on both sides with soft, stretchy, fabric and don’t add any rigid electrical components, you get comfort and wearability. So, they set out to see if they could turn a sheer, stretchy fabric into electrodes.
The team started with an ultrasheer knit fabric that could be stretched up to 200% and still return to its original shape. The fabric was 87% nylon and 13% spandex—think pantyhose. The nylon added strength, the spandex added stretch and resiliency. Using a two-step chemical process common in printing circuit boards, they coated the fibers in the knit fabric with a layer of gold just 100nm thick. Gold conducts electricity but is biocompatible and chemically stable, so it’s safe for use in clothing.
High-resolution pictures showed that the gold uniformly covered the fibers, and before-and-after tests revealed that the coating didn’t really impact the fabric’s softness and stretchability. The coated fabric was highly conducting even after it was repeatedly stretched, which suggested that it would work well in a wearable device.
Taking this project to the next level, the team fabricated two pieces of gold-coated fabric as top and bottom electrodes. Between the electrodes, the team sandwiched a thin, elastic emissive layer that emitted blue light in response to a low current. The three layers were sealed inside of a thin layer of soft, transparent rubber to prevent stray current leaks. The end result was a soft, lightweight, thin, wearable material that glowed even when stretched by as much as 200%.
The researchers noticed that brightness varied with stretching, in part because the electrodes were more transparent when stretched. But even at its dimmest, the glow was clearly visible.
In a creative exploration of just some of the possibilities, the researchers demonstrated a cost-effective way to pattern designs in the fabric. They painted some areas of the nylon-spandex fabric with a wax mixture before covering it in gold. The wax kept the gold from adhering, so after it was removed and the layers were assembled, the once-wax covered areas stayed dark while the rest of the fabric lit up. In addition, they showed that you can adhere a patterned top electrode to the rest of the device in such a way that it can be easily peeled off and replaced with a differently-patterned electrode!
Smart + versatile + comfy? I only have one more question. Is it dry clean only?*
This video shows a light-emitting sheer fabric with a changeable display pattern. Credit: The Carmichael Lab.
*According to the researchers, initial tests show that normal washing and drying may be possible, but more testing is needed.
“What’s going on in this video? Our science teacher claims that the pain comes from a small electrical shock, but we believe that this is due to the absorption of light. Please help us resolve this dispute!”
(We’ve since updated this article to include the science behind vegan ice cream. To learn more about ice cream science, check out The Science of Ice Cream, Redux)
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