11 Mar 2020
University of Windsor uses textile structure as integral part of illuminated elements.University of Windsor in Ontario.
The fabrication of wearable e-textiles and smart clothing has until now been hindered by a number of factors, including the porous structures and non-planar surfaces of the textiles themselves. The Windsor project tackled the problem by using the textile structure as an integral part of wearable device design. The findings were published in Matter.
"Users want light-emitting displays that are integrated into fabrics so that they are still soft, lightweight, stretchable, washable, and wearable; just like ordinary clothing but with light-emitting panels that can illuminate the user or display graphics," said Tricia Carmichael from the University of Windsor.
One issue with this in practice has been the inherent stiffness of light-emitting structures, making it difficult for a fabric incorporating them to remain able to move and stretch. So the Windsor team took a different approach, using a sheer nylon and spandex fabric as the substrate for a transparent conductor.
"We coat the open framework structure of an ultrasheer knitted textile with a conformal gold film using solution-based metallization, to form gold-coated ultrasheer electrodes that are highly conductive and retain conductivity to 200-percent strain," said the project in its published paper.
The team then used the gold-coated ultrasheer fabric as both top and bottom transparent electrodes sandwiching an elastomeric emissive layer, producing "lightweight, wearable, light-emitting e-textiles that function to the strain limit of the textile."
Patterned light emission is a key aspect of wearable luminous clothing, so the project used a stencil-printing method to deposit a wax resist over certain areas of the fabric before metallization, shielding those areas from the gold coating while the remainder is treated. Removal of the wax then leaves behind a fabric capable of patterned emission.
In trials, this approach successfully created a fabric displaying static illuminated patterns such as a smiley-face emoji. The team also fabricated a dynamic seven-segment display, by patterning seven rectangular segments on the fabric snd then selectively operating them in different combinations to display changing numerals.
A textile-centric approach to wearable electronics could allow a broad range of natural and synthetic materials to be knitted, woven, tufted, and braided into a variety of light-emitting structures, while exploiting the ability to tailor paramters such as fiber density, composition and durability.
"We are optimistic about the ability to scale up the technology," commented Carmichael. "The process we use to deposit the ultrathin gold coating on fabric fibers can be scaled up by increasing the volume of the plating solution, enabling processing of entire articles of clothing. We also use existing ultrasheer fabrics and thus do not require new textile manufacturing."
One significant remaining hurdle could be ways of incorporating wearable light-emitting devices into everyday life in general, and do so without bulky energy generators and storage systems. The University of Windsor team intends to tackle this as part of its future work.
"We are exploring the wide variety of textile architectures as an integral part of device electrode design to enable the seamless integration of energy storage materials into textiles," said Carmichael.