Recently, scientists at Rice University have made a better epoxy resin for electronic applications. By combining the epoxy resin invented by Rice Laboratory of chemist James Tour with the "super" graphene foam material, a new conductive composite material, which is much stronger than pure epoxy resin, is better than other epoxy resin composite materials, and has low material density.
Epoxy resin itself is an insulator and is usually used in coatings, adhesives, electronics, industrial tools and structural composites. Metal or carbon fillers are usually added for applications requiring electrical conductivity, such as electromagnetic shielding applications. But there is a trade-off: more fillers bring better conductivity at the cost of weight and compressive strength, while composites become more difficult to process.
The solution of Les (Rice) laboratory uses a three-dimensional foam made of nano graphene to replace metal or carbon powder. Graphene is carbon thin plate with only one carbon atom of thicknesses.
The Tour laboratory has collaborations with materials scientist Pulickel Ajayan and Rouzbeh Shahsavari of Rice University, Lou Jun and Zhaoyan of Beihang University, and has drawn inspiration from epoxy resin injection into three dimensional scaffolds, including graphene aerogels, foam and various process scaffolds.
The new technology uses polyacrylonitrile (Pan) to make stronger scaffolds. Polyacrylonitrile, a powdered polymer resin, is used as a carbon source and mixed with nickel powder. In a four step process, they cold press the material to make it dense, heat it in the furnace to turn pan into graphene, chemically treat the resulting material to remove nickel, and use vacuum to pull epoxy resin into existing porous materials.
"Graphene foam is a single layer graphene," Tour said. "So, in fact, the whole bubble is a large molecule. When epoxy resin penetrated the foam and then hardened, any bending of epoxy resin in one position would exert stress on the other parts because of the embedded graphene scaffolds. This will eventually harden the whole structure. "
According to researchers, the density of the spherical composite with a foam content of 32% is slightly higher, but the conductivity is about 14 SIEMENS per centimeter (conductivity or reverse ohmus). The foam does not increase the weight of the compound, but the compressive strength is 7 times that of the pure epoxy resin.
The simple interlock between graphene and epoxy resin also helps to stabilize the structure of graphene. "When epoxy resin infiltrated graphene foam and then hardened, epoxy resin was trapped in the micron sized area of graphene foam," Tour said.
The lab enhances the stakes by mixing multi walled carbon nanotubes into graphene foam. The researchers said that the hardness of the composite was 1732% higher than that of pure epoxy resin, and the electrical conductivity of the composite was nearly three times higher than that of pure epoxy resin, which was about 41 Siemens / cm, far higher than almost all the epoxy resin composites based on scaffolds reported so far.
Tour expects the process to be expanded for industrial scale. "People just need a furnace big enough to make the final parts," he said. "But it has always been the case that large metal parts are made by cold pressing and then heating."
He said the material could initially replace carbon composite resin, which is used to pre impregnate and strengthen fabrics in materials from aerospace structures to tennis rackets.