Researchers tame aerogel by freezing it.

Graphene, which was discovered in 2004, is 1 million times thinner than a human hair, 300 times stronger than steel, and is the best known conductor of heat and electricity. Researchers at the University of Buffalo (UB), along with colleagues at Kansas State University and the Harbin Institute of Technology in China, say that these qualities could be used to improve medical diagnostic devices, make computers faster, and batteries more powerful, among other things. But, they say that the material is very light and difficult to manipulate beyond its two-dimensional form.

Fig. 1 – Graphene is incredibly light, here it’s shown resting on top of a cotton-like material. (Credit: University at Buffalo)
Recently, scientists poured a graphene oxide suspension, a gel-like form of the material, into freezing molds to create 3D objects, which works, but only with simple structures that have limited commercial applications. Another option is to mix graphene with a polymer or other thickening agent and use a 3D printer, which helps keep the structure from falling apart. But when the polymer is removed via thermal process, it damages the delicate structure created.

A third option, the one favored by the UB researchers and their team, uses a modified 3D printer and frozen water to create lattice-shaped cubes and a three-dimensional truss with overhangs using graphene oxide. The structures, they say, could be an important step toward making graphene commercially viable in electronics and medical devices. (See Figure 1)

“Graphene is notoriously difficult to manipulate, but the structures we built show that it’s possible to control its shape in three-dimensional forms,” said Chi Zhou, Assistant Professor of Industrial and Systems Engineering at UB’s School of Engineering and Applied Sciences.

In their experiments, the research team mixed graphene oxide with water. They then printed the lattice framework on a surface of -25°C. The graphene is sandwiched between the layers of frozen ice, which act as a structural support. After the process is completed, the lattice is dipped in liquid nitrogen, which helps form even stronger hydrogen bonds. The lattice is then placed in a freeze dryer, where the ice is changed into gas and removed. The end result is a complex, three-dimensional structure made of graphene aerogel that retains its shape at room temperature.

“By keeping the graphene in a cold environment, we were able to ensure that it retained the shape we designed. This is an important step toward making graphene a commercially viable material,” said Dong Lin, Assistant Professor of Industrial and Manufacturing Systems Engineering at Kansas State University.

The researchers plan to build on their findings by investigating how to create aerogel structures formed of multiple materials.

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