By Josh Perry, Editor
[email protected]

Researchers at the University of Wollongong (Australia) developed a smart, flexible composite material that increases its electrical conductivity when deformed and especially when elongated, which makes it potentially ideal for wearable electronics and robotics, according to a report from the university.

Researchers developed a novel smart material with increased electrical and thermal conductivity. (University of Wollongong)

This novel mixture of liquid metal and metallic microparticles overcomes previous challenges in developing conductive, elastic materials where stretching the material caused the conductive filler particles to separate and, therefore, reduce the material’s conductivity.

The solution stemmed from an accident.

“The first step was a mixture of liquid metal, iron microparticles, and elastomer that, by a fortuitous accident, had been cured in an oven for much longer than normal,” the report explained. “The over-cured material had reduced electrical resistance when subjected to a magnetic field, but it took dozens more samples to find that the reason for the phenomena was an extended curing time of several hours longer than it would normally take.”

When the material was stretched, even just a little, its electrical resistance dropped by seven orders of magnitude, according to a researcher. The composite also had increased thermal conductivity that could be used in a portable heater that warms when pressure is applied.

The research was recently published in Nature Communications. The abstract read:

“Conductive elastic composites have been used widely in soft electronics and soft robotics. These composites are typically a mixture of conductive fillers within elastomeric substrates. They can sense strain via changes in resistance resulting from separation of the fillers during elongation. Thus, most elastic composites exhibit a negative piezoconductive effect, i.e. the conductivity decreases under tensile strain. This property is undesirable for stretchable conductors since such composites may become less conductive during deformation.

“Here, we report a liquid metal-filled magnetorheological elastomer comprising a hybrid of fillers of liquid metal microdroplets and metallic magnetic microparticles. The composite’s resistivity reaches a maximum value in the relaxed state and drops drastically under any deformation, indicating that the composite exhibits an unconventional positive piezoconductive effect.

“We further investigate the magnetic field-responsive thermal properties of the composite and demonstrate several proof-of-concept applications. This composite has prospective applications in sensors, stretchable conductors, and responsive thermal interfaces.”