With a wall thickness of about 160nm, this closed-cell, plate-based nanolattice structure provides the first experimental verification that such arrangements can reach the theorized limits of strength and stiffness in porous materials. Image: Cameron Crook and Jens Bauer/UCI.Researchers at the University of California, Irvine (UCI) and several other institutions have architecturally designed plate-nanolattices – nanometer-sized carbon structures – with a ratio of strength to density that makes them stronger than diamond.
In a recent paper in Nature Communications, the researchers report success in conceptualizing and fabricating the nanolattices, which consist of closely connected, closed-cell plates instead of the cylindrical trusses common in such structures over the past few decades.
"Previous beam-based designs, while of great interest, had not been so efficient in terms of mechanical properties," said corresponding author Jens Bauer, a UCI researcher in mechanical & aerospace engineering. "This new class of plate-nanolattices that we've created is dramatically stronger and stiffer than the best beam-nanolattices."
According to the paper, the team's design can improve on the average performance of cylindrical beam-based architectures by up to 639% in strength and 522% in rigidity. Members of the architected materials laboratory of Lorenzo Valdevit, professor of materials science & engineering as well as mechanical & aerospace engineering at UCI, verified their findings using a scanning electron microscope and other technologies provided by the Irvine Materials Research Institute.
"Scientists have predicted that nanolattices arranged in a plate-based design would be incredibly strong," said lead author Cameron Crook, a UCI graduate student in materials science & engineering. "But the difficulty in manufacturing structures this way meant that the theory was never proven, until we succeeded in doing it."
According to Bauer, the team's achievement rests on a complex 3D laser printing process called two-photon lithography direct laser writing. As a laser is focused inside a droplet of an ultraviolet-light-sensitive liquid resin, the material becomes a solid polymer at points where it is simultaneously hit by two photons. By scanning the laser or moving the stage in three dimensions, the technique is able to render periodic arrangements of cells, each consisting of assemblies of plates as thin as 160nm.
One of the group's innovations was to include tiny holes in the plates that could be used to remove excess resin from the finished material. As a final step, the lattices go through pyrolysis, in which they're heated to 900°C in a vacuum for one hour. The end result is a cube-shaped lattice of glassy carbon that has the highest strength scientists ever thought possible for such a porous material.
Bauer said that another goal and accomplishment of the study was to exploit the innate mechanical effects of the base substances. "As you take any piece of material and dramatically decrease its size down to 100nm, it approaches a theoretical crystal with no pores or cracks. Reducing these flaws increases the system's overall strength," he said.
"Nobody has ever made these structures independent from scale before," added Valdevit, who directs UCI's Institute for Design and Manufacturing Innovation. "We were the first group to experimentally validate that they could perform as well as predicted while also demonstrating an architected material of unprecedented mechanical strength."
Nanolattices hold great promise for structural engineers, particularly in aerospace, because it's hoped that their combination of strength and low mass density will greatly enhance aircraft and spacecraft performance.
This story is adapted from material from the University of California, Irvine, with editorial changes made by Materials Today. The views expressed in this article do not necessarily represent those of Elsevier. Link to original source.