By Josh Perry, Editor
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An international team of researchers affiliated with the Ulsan (South Korea) National Institute of Science and Technology (UNIST) has demonstrated through modeling and experimentation that folding monolayer graphene films allows them to be incorporated on polymer composites and improves mechanical reinforcement.

From left are Chunhui Wang, Bin Wang, Distinguished Professor Rodney S. Ruoff, Benjamin Cunning, and Yi Jiang. (Kyoungchae Kim)

According to a report on the UNIST website, the researchers folded an A5-sized, 400 nanometer thick polycarbonate film in half 12 times and saw improved stiffening, strengthening, and toughening from the folded graphene.

The premise for the study came from a high schooler in California in 2002, who demonstrated that a single piece of paper that was 1,200 meters long could be folded in half 12 times. It was previously thought that the limit was seven folds.

Researchers started by folding the polycarbonate film in half 12 times, which produced a millimeter-thick material, and then filled the laminate by adding a polycarbonate film that had been coated with graphene through chemical vapor disposition.

“With a remarkably low volume fraction of graphene of only 0.085% (less than 1 part in 1,000), the Young’s modulus (intrinsic stiffness), strength (stress that the material breaks at), and toughness modulus (energy consumed in breaking the sample) were enhanced in the folded composite by an average of 73.5%, 73.2%, and 59.1%, respectively,” the article explained.

It added, “From the graphene folds alone the Young’s modulus was increased by 24.2%, strength by 25.4%, and toughness modulus by 14.5%. Note that these values are lower bounds, from the team’s modeling. Thus, a remarkable mechanical reinforcement from the combined folding and stacking of graphene was found.”

The research was recently published in Advanced Materials. The abstract stated:

“A folding technique is reported to incorporate large?area monolayer graphene films in polymer composites for mechanical reinforcement. Compared with the classic stacking method, the folding strategy results in further stiffening, strengthening, and toughening of the composite.

“By using a water–air?interface?facilitated procedure, an A5?size 400 nm thin polycarbonate (PC) film is folded in half 10 times to a ≈0.4 mm thick material (1024 layers). A large PC/graphene film is also folded by the same process, resulting in a composite with graphene distributed uniformly. A three?point bending test is performed to study the mechanical performance of the composites.

“With a low volume fraction of graphene (0.085%), the Young's modulus, strength, and toughness modulus are enhanced in the folded composite by an average of 73.5%, 73.2%, and 59.1%, respectively, versus the pristine stacked polymer films, or 40.2%, 38.5%, and 37.3% versus the folded polymer film, proving a remarkable mechanical reinforcement from the combined folding and reinforcement of graphene.

“These results are rationalized with combined theoretical and computational analyses, which also allow the synergistic behavior between the reinforcement and folding to be quantified. The folding approach could be extended/applied to other 2D nanomaterials to design and make macroscale laminated composites with enhanced mechanical properties.”