All Structures Strong And Small

Hoping to bring the exquisite order and strength of the Eiffel Tower’s architecture to ultralight materials, researchers have created metal lattices with a framework that is strong and stiff, yet mostly air (Science, DOI: 10.1126/science.1211649). The novel nickel structures, which are lightweight and surprisingly springy, could have applications as aerospace structural components, thermal insulation, battery electrodes, catalyst scaffolds, and damping materials.

The random sizes and shapes of internal air pockets in previous ultralight materials, such as aerogels or metal foams, sap the materials of stiffness and strength. A team led by Tobias A. Schaedler, of HRL Laboratories, in Malibu, Calif., sought to bring those properties to lightweight materials by imposing order.

Structures such as the Eiffel Tower and the Golden Gate Bridge “are incredibly light by virtue of their architectures. We are trying to make new and improved materials by bringing this concept to materials’ architecture at the micro- and nanoscale,” Schaedler says.

The lightest material the team prepared is 200 times lighter than Styrofoam. It’s 99.99% air, Schaedler points out, and the nickel in the structure is just 100 nm thick.

The researchers make the metal microlattices by taking a reservoir of photopolymerizable monomer and covering the reservoir with a mask containing small holes. They then shine light through the holes. Wherever the light hits the monomers they polymerize, and the polymer forms a strut along the path of the light. The researchers then wash out remaining monomer, coat the struts in a thin layer of nickel, and dissolve the polymer. “By altering the mask pattern, the hole size, and the angle of incident light, we can easily modify the shape of this lattice,” Schaedler notes.

“These materials are unique in that they achieve aerogel-like densities with highly regular structures,” comments Bryce C. Tappan, an expert in lightweight metal foams at Los Alamos National Laboratory. They “offer intriguing possibilities such as in small-scale energy absorption and also serve to further our fundamental understanding of how materials behave on the microscale,” he adds.