The fabric of the future would be able to change colour on demand, acting as status indicators or even doubling as displays.
Researchers from UC Berkeley in California and Google engineers have developed a new colour-changing thread which they have called Ebb. The colour-shifting threads have various hues in response to electrical charges.
Ebb is part of Google's Project Jacquard spin-off, which aims to create "smart textiles" using standard, industrial looms. The goal is to transform everyday fabric-based objects into interactive surfaces. The basis of Project Jacquard is conductive yarns, which combine thin, metallic alloys with conventional natural and synthetic yarns. Indistinguishable from traditional yarns, these conductive yarns can be used to weave enhanced areas into precise locations on the textile.
The Ebb thread is an extension of the conductive thread. The scientists coated conductive threads made of cotton thread wound with copper with thermochromic pigments. When electricity is run through the conductive threads, they heat up. The thermochromic pigments change from an opaque to a transparent state, revealing the colour of the original thread under the coating. When the power is removed, the pigment cools down, reverting to its opaque colour.
As a result, it is possible to maintain the threads in the colours of the thermochromic pigments without applying power, but activating the pigment to reveal the original thread's colour requires power.
The use of thermochromic pigments is not new. However, most previous approaches utilised heating elements to actuate the colour change, impacting the flexibility and integrity of the fabrics. Another approach has been to use conductive threads, but paint the fabric surface with thermochromic inks after the threads had been weaved in.
By coating the conductive threads with thermochromic ink before weaving them in, the scientists were able to integrate them using a wider range of fabric production techniques.
The researchers then experimented with weaving and crocheting the thread in various ways, then controlling individual threads to create non-emissive textile displays. In certain weaves, the researchers were able to create the effect of a slow animation as the colour changes move across the thread. In others, they were able to display information in abstract ways. For example, they weaved the threads into segmented digits, similar to the liquid crystal displays on clocks, in order to display numbers by changing the colours of the segments.
For now, the threads change colours slowly and subtly, so it is not possible to create fast, responsive displays. But the researchers hope to accelerate the effect, with the goal of making the refresh rates comparable to e-ink, which would be fast enough to be used as displays to provide indications of status changes.
Additionally, the thermochromic pigment used is activated at 30 degrees Celsius, and so the resulting fabrics are volatile, responding to heat generated from any source, not just electricity running through the threads.
"A cold wind could blow a computationally generated pattern off the fabric, or body heat could induce change in particular locations," the researchers noted.
Additionally, the pigments currently have a limited life pan, with the transparent state becoming permanent after the threads have been heated around 500 times.