Researchers at a Cornell lab have applied for patent protection for the colour ‘ultrablack’ using biomimicry by following the magnificent riflebird’s ’s feathers, which absorb most of the light that hits them. The colour can be used on natural materials, including wool, silk and cotton.
The colour “ultrablack” – defined as reflecting less than 0.5% of the light that hits it – has a variety of uses, including in cameras, solar panels and telescopes, but it’s difficult to produce and can appear less black when viewed at an angle.
THE RESEARCH: Researchers at the Responsive Apparel Design (RAD) Lab, in the College of Human Ecology (CHE), analysed the feathers of the riflebird, a member of the bird-of-paradise family found in New Guinea and Australia, and realised that its striking black plumage comes from melanin pigment combined with tightly bunched barbules that serve to deflect light inward, absorbing nearly all of it. This renders the bird extraordinarily black, but only when viewed straight on; at an angle, its plumage appears shiny.
This same coloration is evident in other creatures, including fish and butterflies. The research team’s choice of polydopamine, a versatile polymer, for their dye was intentional as it is a synthetic melanin. The riflebird has these really interesting hierarchical structures, the barbules, along with the melanin and they wanted to combine those aspects in a textile.
THE METHODOLOGY: The researchers dyed a white merino wool knit fabric with polydopamine, followed by etching of the material in a plasma chamber to create nanofibrils – spiky nanoscale growths. These features were made to mimic the light-trapping capabilities found on the riflebird’s ultrablack feathers, which absorb most of the light that hits them.
A two-step approach by the team produced the darkest fabric currently reported; it’s also easy to manufacture, scalable, wearable and not angle-dependent. Analysis of the material was conducted at the Cornell Center for Materials Research and Human Centered Design shared instrumentation facility.
The analysis revealed that the group’s fabric had an average total reflectance of 0.13%, making it the darkest fabric yet reported. And it remained ultrablack across a 120-degree angular span, meaning it appears the same at up to a 60-degree angle either side or straight on, superior to currently available commercial materials.
The researchers have applied for patent protection with the Cornell Center for Technology Licensing (CTL) and hope to form a company around their process, which can be used on natural materials, including wool, silk and cotton.
Potentially speaking: The ultrablack fabric has potential in many solar thermal applications, converting and utilizing absorbed light into thermal energy. It could also be used for thermo-regulating camouflage.
THE TEAM: The findings were published in a report — Ultrablack Wool Textiles Inspired by Hierarchical Avian Structure — in Nature Communications. RAD Lab’s Director Larissa Shepherd is the senior author, along with co-authors who are doctoral students and RAD Lab members — Hansadi Jayamaha and Kyuin Park.
