New breakthrough in hyper-flexible graphene membrane of Zhejiang University with high thermal conductivity

Recently, the team of high-polymer professors at Zhejiang University developed a high-conductivity ultra-flexible graphene membrane with a thermal conductivity of up to 2053W/mK, which is close to 40 % of the ideal single-layer graphene thermal conductivity, creating a macroscopic material. New record of thermal conductivity; At the same time, the material is assembled from a micropleated large graphene, which is super flexible and can be repeatedly folded 6,000 times and subjected to bending 100,000 times.

This latest achievement has solved the worldwide problem that macromaterials can not be combined with high thermal conductivity and high flexibility. It is expected to obtain important applications in such fields as efficient heat management, new generation flexible electronic devices, andspecial. The article was published in AdvancedMaterials. The first author of the paper was doctoral student Pengli.

Electrical appliances will heat up when they work and require efficient heat management to ensure their normal operation. The new generation of devices also requires bending. Therefore, it is very important to study high thermal conductivity and high flexibility materials. However, the existing macromaterials of high thermal conductivity and high flexibility is a pair of contradictions, fish and bear Palm are often difficult to have both. For example, metal materials have good ductility, but their maximum thermal conductivity is about 429W/mK. Some inorganic ceramic materials have higher thermal conductivity but are very brittle.

The emergence of graphene provides theoretical possibilities for solving this contradiction. This major scientific problem was recently overcome by the team of superb professors. They creatively proposed the idea of "large microfolds": large areas of graphene have fewer defects and can achieve high thermal conductivity; The microfold allows the material to have enough strain space when bending and bending to ensure high flexibility.

He told China Science that this new idea was easy to achieve. Three steps can be completed: 1) Large amounts of graphene oxide water dispersion solution are scratched into a film; 2) High-temperature heat treatment, the oxygen-containing functional group in the membrane decomposes at high temperatures, releasing gas. At the same time, with the increase of temperature, the graphene defect structure is gradually repaired, and the gas is blocked inside the graphene membrane due to expansion. Form microbags; 3) The mechanical roll is pressed into the film, and the gas of the microballoon is discharged under the added pressure to form a micro-fold.

Microfolds are often stress concentration points. Under the action of external forces, folds will produce elastic deformation, and local folds will be stretched out to form permanent deformation. The greater the stress, the more folds that are stretched, the more obvious the elastic deformation and permanent deformation. The comparison shows that the fracture elongation of graphene membrane with a large number of microfolds is 2 to 3 times higher than that of traditional GPI membrane, and the maximum value can reach 16 %. The ductility of graphene microfolds allows it to tolerate multiple complex deformation such as repeated folding, knotting, distortion, repeated bending of knuckles, and Origami.

The thermal conduction mode of graphene is phonon conduction, and boundaries, voids, functional groups, etc. are defects of phonon escape. For this purpose, the researchers used a non-fragmented large area of graphene oxide as a raw material to reduce the escape of edge phonons. At the same time, high-temperature heat treatment is used to remove the functional groups on the surface of graphene and repair the internal holes in graphene to obtain a less defective graphene structure. These structural changes were confirmed by Raman, XRD and TEM. The average thermal conductivity of the graphene membrane was 1900 W/mK, and the highest value reached 2053 W/mKm. 1, exceeds the thermal conductivity of the best GPI membrane and other macromaterials.

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