Stretchable 'thubber' could give electronics soft touch

Researchers in the US have developed a thermally conductive rubber material, a breakthrough that could help in the creation of soft, stretchable machines and electronics.

Navid Kazem (left), Malen (centre), and Majidi (right) demonstrate the elasticity of 'thubber’
Navid Kazem (left), Malen (centre), and Majidi (right) demonstrate the elasticity of 'thubber’

The team, which includes Carmel Majidi and Jonathan Malen of Carnegie Mellon University, describes its findings in Proceedings of the National Academy of Sciences.

Dubbed ‘thubber’ the new material is said to be an electrically insulating composite that exhibits metal-like thermal conductivity and elasticity similar to soft, biological tissue. It can also stretch over six times its initial length.

"Our combination of high thermal conductivity and elasticity is especially critical for rapid heat dissipation in applications such as wearable computing and soft robotics, which require mechanical compliance and stretchable functionality," said Majidi, an associate professor of mechanical engineering.

According to CMU, thubber could be applied to athletic wear and sports medicine, but the material could be further utilised in advanced manufacturing, energy and transportation.

"Until now, high power devices have had to be affixed to rigid, inflexible mounts that were the only technology able to dissipate heat efficiently," said Malen, an associate professor of mechanical engineering. "Now, we can create stretchable mounts for LED lights or computer processors that enable high performance without overheating in applications that demand flexibility, such as light-up fabrics and iPads that fold into your wallet."

The key component in thubber is a suspension of non-toxic, liquid metal microdroplets. The liquid state allows the metal to deform with the surrounding rubber at room temperature. When the rubber is pre-stretched, the droplets form elongated pathways that are efficient for heat travel. Despite the amount of metal, the material is also electrically insulating.

To demonstrate these findings, the team mounted an LED light onto a strip of the material to create a safety light worn around a jogger's leg. The thubber dissipated the heat from the LED, which would have otherwise burned the jogger. The researchers also created a soft robotic fish that swims with a thubber tail, without using conventional motors or gears.

"As the field of flexible electronics grows, there will be a greater need for materials like ours," said Majidi. "We can also see it used for artificial muscles that power bio-inspired robots."

The team’s paper - High thermal conductivity in soft elastomers with elongated liquid metal inclusions – is available here.