Traditional materials usually experience an increase in the distance between internal particles during stretching, which lengthens the pathways for electron and heat transport; as a result, their electrical and thermal conductivity tend to decrease. However, a new nanocomposite developed by a South Korean research team exhibits the opposite behavior: after the material is stretched, its electrical conductivity and thermal conductivity both increase. The team further applied it to thermal management in foldable phones, offering a potential new material solution for heat dissipation in flexible electronic devices.
The study was led by Professors Seunghyun Baik and Joonmyung Choi from the School of Mechanical Engineering at Sungkyunkwan University, and the results were published in Advanced Functional Materials.
Nanoscale Gaps Make Heat Transport More Efficient After Stretching
The research team uniformly dispersed silver nanoparticles with a particle size of only 3.4 nm in stretchable silicone rubber and controlled the spacing between the particles to about 4.1 nm. When the spacing between nanoparticles is reduced to below 10 nm, electrons can cross the energy barrier between particles through quantum tunneling, enabling electron transport. This allows the material to maintain relatively good electrical conductivity even when it deforms.
More notably, the team found that in the stretched state, heat transport inside the composite also changed in a way different from that in traditional materials. The nanoscale heat-transfer channels formed between particles allow heat to be transferred between fillers in a ballistic-like transport manner, reducing additional scattering during stretching and thereby increasing the material's thermal conductivity.
Stretching Can Also Control the Material's Thermal Conductivity
The team further adjusted the spacing between silver particles and the chemical properties of the silicone rubber, giving the composite a thermal switching property, meaning that heat transport can be regulated by changing the stretching state of the material. Computational simulations showed that after stretching, polymer chains become oriented along the strain direction, allowing heat to be transported more efficiently along that direction.
This property has potential application value for flexible electronic devices such as foldable and stretchable devices. Smartphones and electronic devices continuously generate heat during operation, and for bendable and foldable devices, the performance of traditional heat-dissipation materials may be affected after the devices deform. If thermal conductivity can be actively regulated through mechanical deformation, it may be possible to further improve the thermal management capability of flexible electronic devices.