Least Dense 3D-Printed Graphene Structure Enabled by New Technique

Time: 2017-07-10
Summary: At one-atom thick, graphene is the lightest and strongest material in the world. Harnessing its power, however, has not been easy as it’s not a simple process to manipulate the world’s toughest material. Additive manufacturing (AM) may hold the answer.
At one-atom thick, graphene is the lightest and strongest material in the world. Harnessing its power, however, has not been easy as it’s not a simple process to manipulate the world’s toughest material. Additive manufacturing (AM) may hold the answer.

Various researchers are currently working to find ways to 3D print the “wonder material,” as it is sometimes called, in ways that maintain its desired physical properties. Most methods involve processing graphene as an aerogel, which ultimately reduces the amount of graphene in the final composition to just 20 percent or so.

A 3D-printed square of graphene aerogel so light that it can rest on an individual awn of wheat without bending it. The print was made by engineers from Kansas State University, the University at Buffalo and Lanzhou University in China.

A 3D-printed square of graphene aerogel so light that it can rest on an individual awn of wheat without bending it. The print was made by engineers from Kansas State University, the University at Buffalo and Lanzhou University in China.
At University at Buffalo,a new process has been developed that maintains the physical properties of graphene and enables the 3D printing of macroscale structures. In fact, the parts printed with the process have been dubbed by the Guinness World Records as the “least dense 3D-printed structure” yet made. 

3D Printing with Graphene
To understand what makes Zhou’s method so unique, it’s important to understand why 3D printing graphene has been so difficult traditionally. Zhou explained that, until recently, it’s been an issue of bonding the material layer by layer.

 
“The major difficulty of printing graphene is caused by the complex graphene morphology and nontrivial material forming mechanism,” Zhou said. “It is very challenging, if not impossible, to assemble the 2D graphene sheets by heat fusing, photocuring, chemical bonding as is typically used in traditional 3D printing technologies.”

Previous research has included work by the Imperial College London and Lawrence Livermore National Laboratory (LLNL). The Imperial College London team 3D prints using graphene-oxide combined with a responsive polymer to extrude the material as a paste. 

Freeze-Casting Graphene
However, Zhou’s group—which also included Dong Lin from Kansas State University and Qiangqiang Zhang from Lanzhou University in China—took a different approach. The team modified an open-source fused filament fabrication 3D printer to use an inkjet printhead, rather than an extrusion head, to deposit a graphene oxide and water mixture in a freezer on a cold plate at -20°C.

The low temperatures aid the object in keeping its shape and as the ice crystals grow, they squeeze the graphene sheets that make up each layer into a 3D network.Upon printing, the structure is freeze dried, causing the ice to evaporate and leaving only a graphene aerogel.

This process, known as freeze-casting, is sometimes used in ceramics. Water solidifies in an anisotropic manner and, when combined with another material, such as ceramic particles, in a slurry, it’s possible to directionally control the temperature. Ice crystals form on one side and spread across a temperature gradient on the material, redistributing the particles of the mixture in the process.

“The end result is graphene aerogel, a porous and superlight material in which the liquid part of the gel is replaced by air, allowing it to retain its shape at room temperature,” Zhou said.“The process has proven to be very effective and successful.One of the blocks along the way is the proper thermal management, which is the key to the process performance (reliability, resolution and integrity).”

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