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Discrete and Process Automation

Century-Old Theory Comes to Life with 3D Printers

16 November 2017

Engineers from Rice University have used 3D printers to turn structure that only existed in theory into strong, light and durable materials with complex, repeating patterns.

The porous structures, called schwarzites, are designed with computer algorithms. Rice researchers found they could send data from the programs to printers and make macroscale polymer models for testing. Their samples strive to use as little material as possible and still provide strength and compressibility.

From left, Rice University researchers Chandra Sekhar Tiwary, Seyed Mohammad Sajadi, Peter Owuor, Pulickel Ajayan and Robert Vajtai hold samples of 3-D printed schwarzites, porous blocks based on complex mathematical models created in the 19th century and further developed in the 20th. The materials retain their strength at any scale, from the nano to the macro. (Jeff Fitlow/Rice University)From left, Rice University researchers Chandra Sekhar Tiwary, Seyed Mohammad Sajadi, Peter Owuor, Pulickel Ajayan and Robert Vajtai hold samples of 3-D printed schwarzites, porous blocks based on complex mathematical models created in the 19th century and further developed in the 20th. The materials retain their strength at any scale, from the nano to the macro. (Jeff Fitlow/Rice University)

The results of this research may someday lead to nanoscale electronic devices, catalysts, molecular sieves and battery components and on the macroscale could become high-load-bearing, impact-resistant components for buildings, cars and aircraft.

Someday it may be possible to print an entire building as one schwarzite “brick.”

Schwarzites are mathematical marvels that have inspired a lot of organic and inorganic constructs and materials. The discovery at Rice of the buckminsterfullerene (or buckyball) provided further inspiration for scientists to explore the design of 3D forms from 2D structures.

These structures remained theoretical until 3D printers provided the first practical way to make them. The Rice lab of materials scientist Puickel Ajayan, in collaboration with researchers at the University of Campinas, São Paulo, investigated the bottom-up construction of schwarzites through molecular dynamics simulators and then printed the simulations in the shapes of polymer cubes.

"The geometries of these are really complex; everything is curved, the internal surfaces have negative curvature and the morphologies are very interesting," said Rice postdoctoral researcher Chandra Sekhar Tiwary, who led an earlier study that showed how seashells protect soft bodies from extreme pressure by transferring stress throughout their structures.

"Schwarzite structures are very much the same," he said. "The theory shows that at the atomic scale, these materials can be very strong. It turns out that making the geometry bigger with polymer gives us a material with a high load-bearing capacity."

Schwarzites displayed excellent deformation characteristics, according to Tiwary, “The way a material breaks is important. You don't want things to break catastrophically; you want them to break slowly. These structures are beautiful because if you apply force to one side, they deform slowly, layer by layer.

"You can make a whole building out of this material, and if something falls on it, it's going to collapse slowly, so what's inside will be protected," he said.

Because they can take many forms, the Rice team limited its investigation to primitive and gyroid structures, which have periodic minimal surfaces as originally conceived by Schwarz. In tests, both transferred loads across the entire geometry of the structures, no matter which side was compressed.

That was an unexpected result. Douglas Galvão, a professor at the University of Campinas, who studies nanostructures through molecular dynamics simulations, originally suggested the project when Tiwary visited the Brazil campus as a research fellow through the American Physical Society and Brazilian Physical Society.

"It is a little surprising that some atomic-scale features are preserved in the printed structures," Galvão said. "We discussed that it would be nice if we could translate schwarzite atomic models into 3-D printed structures. After some tentatives, it worked quite well. This paper is a good example of effective theory-experiment collaboration."

The researchers said the next step will be to refine the surfaces with higher-resolution printers and further minimize the amount of polymer to make the blocks even lighter. In the future, they envision printing 3D schwarzites with ceramic and metallic materials on a grander scale.

"There's no reason these have to be blocked," said co-author and Rice graduate student Peter Owuor. "We're basically making perfect crystals that start with a single cell that we can replicate in all directions."

This research was published in Advanced Materials and can be accessed here.

To contact the author of this article, email Siobhan.Treacy@ieeeglobalspec.com


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