Things are supposed to expand when heated. Nearly all solid materials from rubber and glass would expand when exposed to heat. Only a few materials shrink with heat such as cold water, contracting when heated between 0 and 4 degrees Celsius before expanding.
A team of researchers, however, has developed a 3D-printed material that features a unique property that causes it to shrink when heated. This new material has promising applications in a range of industries.
In a study published in the journal Physical Review Letters on Oct. 21, researchers described how they printed lightweight metamaterials with negative thermal expansion using 3D. A metamaterial is engineered to have a property that is not found in naturally occurring materials.
The new material, which can be can be tuned to contract over a range of temperatures, was made using a 3D printing process known as projection microstereolithography. Researchers printed a bi-material microlattice structure from a polymer and polymer/copper composite that has the ability to flex inward, causing the entire material to shrink when exposed to heat.
"They fabricated their design using a recently developed 3D printing method that prints using two different materials," explained Physics contributing editor Katherine Wright. "They printed the struts and the frame from the same polymer but mixed copper nanoparticles into the frame material. The nanoparticles decreased the frame's thermal expansion, creating enough of a mismatch with the struts to trigger the expected folding."
The researchers already see potential applications for the negative thermal expansion material. The metamaterial, for instance, can be used to passively secure parts in microchips without the need for active heating or cooling to prevent them from coming loose.
"Printed circuit boards can heat up when there's a CPU running, and this sudden heating could affect their performance," explained study researcher Nicholas Fang from the Massachusetts Institute of Technology. "So you really have to take great care in accounting for this thermal stress or shock."
The material can also be used to make dental fillings more secure when the patient eats hot food as well as a means to replace thermal expansion spaces in bridges and buildings with solid padding.
"In this work, aided with multimaterial projection microstereolithography, we experimentally fabricate lightweight multimaterial lattices that exhibit significant negative thermal expansion in three directions and over a temperature range of 170 degrees," the researchers wrote in their study. "Such NTE is induced by the structural interaction of material components with distinct thermal expansion coefficients."
