By imitating the brick-and-mortar molecular structure found in seashells, University of Michigan researchers have created a composite plastic that is as strong as steel but lighter and transparent. It is made of layers of clay nanosheets and a water-soluble polymer that shares chemistry with white glue.

According to Professor Nicholas Kotov, professor of chemical engineering, materials science, and biomedical engineering at the University of Michigan, the laminate can be machined very much as laminates made from carbon fibers are machined in the aviation industry.

The tensile strength of the new material equals that of many steel alloys, however its density is just one-third of steel. Though current manufacturing techniques are relatively slow, Professor Kotov and his development team have devised ways to accelerate it. Potential applications include LEDs, and other optoelectronic devices requiring flexibility and elasticity — also implantable devices that require high-strength materials.

Professor Kotov almost named it "plastic steel," but the new material is not quite elastic enough to deserve that name. Nevertheless, he said its further development could lead to lighter, stronger armor for soldiers and police, and their vehicles.

The researchers created this new composite plastic with a machine they developed that builds materials one nanoscale layer after another. The robotic machine consists of an arm that hovers over a wheel of vials of different liquids. In this case, the arm held a piece of glass about the size of a stick of gum on which it built the new material. The arm dipped the glass into the glue-like polymer solution and then into a liquid that was a dispersion of clay nanosheets. After those layers dried, the process repeated. It took 300 layers of each glue-like polymer and the clay nanosheets to create a piece of this material as thick as a piece of plastic wrap.

The structure of the "nanoglue" and the clay nanosheets enabled the layers to form cooperative hydrogen bonds, which gives rise to what Kotov called "the Velcro effect." Such bonds, if broken, can reform easily in a new place. The Velcro effect is one reason the material is so strong. Another is the arrangement of the nanosheets. They are stacked like bricks, in an alternating pattern.

Currently, work is under way examining the nanomechanical behavior and potential applications in aviation.

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