IR Light Remotely Controls Curvature of Plastics

A new technique has been developed that uses infrared light to curve 2D plastic sheets into 3D structures such as spheres, tubes, or bowls.

Researchers at North Carolina State University are building on previous research that focused on self-folding 3D structures.

Light triggers plastics to fold into curved shapes. Courtesy of Amber Hubbard / North Carolina State University.

In a 2011 paper, NC State researchers Michael Dickey and Jan Genzer outlined a technique in which a conventional inkjet printer was used to print bold black lines onto a pre-strained plastic sheet. The plastic sheet was then cut into a desired pattern and placed under an infrared light. The printed lines absorbed more energy from the infrared light than the rest of the material, causing the plastic to heat and contract, creating a hinge that folded the sheets into 3D shapes.

The advance in their current research is that rather than having the plastic fold along sharp lines — into polygonal shapes such as cubes or pyramids — the plastics bend and curve.

"By controlling the number of lines and the distribution of ink on the surface of the material, we can produce any number of curved shapes," said Dickey. "All of the shapes use the same amount of ink; it's simply a matter of where the ink is applied on the plastic."

The researchers said their work is inspired by nature, as most natural shapes have curvatures. Other researchers have developed techniques for creating self-curving materials using softer materials.

"Our work is the first attempt to accomplish the same using thermoplastics — which are stronger and stiffer than the soft materials,” said Amber Hubbard, a Ph.D. student at NC State. “That makes them more attractive for use in performing some practical actions, such as gripping an object."

The NC State research team has found that the plastics also hold their shape after the light is removed, giving them another advantage over softer materials.

The researchers have developed a computational model that can be used to predict the 3D shape that will be produced by any given printing pattern. Their findings have been published in the Royal Society of Chemistry journal Soft Matter (doi: 10.1039/C7SM00088J).