Modern origami method creates glass shapes by folding

The researchers will present their results today at the spring meeting of the American Chemical Society (ACS).

In earlier work, the researchers used origami and the related technique of kirigami -- which combines cutting with folding -- to shape soft materials made of polymers. "But we wanted to extend these techniques to glass and ceramics, which are much harder to process into complex shapes than polymers," says Tao Xie, Ph.D., the project's principal investigator.

Typically, glass and ceramics are shaped in a mold or are 3D printed in the desired final structure. But a mold can't produce a complicated shape, Xie says. And although 3D printing can do so, it's slow, and an object can be flimsy and need extra support while it's being made. In addition, the printed item usually has a layered texture that might not be the ideal appearance. The team set out to see if they could overcome these shortcomings.

Yang Xu, a graduate student who works in Xie's lab at Zhejiang University, devised a technique in which she mixed nanoparticles of silica -- the main ingredient for making glass -- into a liquid containing several compounds. Curing the mixture with ultraviolet light produced a cross-linked polycaprolactone polymer with tiny beads of silica suspended in it, like raisins in raisin bread.

Next, Xu cut, folded, twisted and pulled on sheets of this translucent polymer composite, which has mechanical properties similar to paper, to make a crane, a feather, a lacy vase and a sphere made of intertwined ribbons, among other objects. If she did this at room temperature, the composite retained its new shape fairly well throughout the remaining production steps. Xu discovered that's because the folding and stretching process irreversibly disrupts the interface between some of the silica particles and the polymer matrix. But if it's critical to fully retain the new shape during the subsequent steps, Xu found that the composite must be heated at about 265 F when it is folded and stretched. That permanently rearranges the links between the polymer chains, firmly fixing the new shape in place.

A subsequent heating step at more than 1,100 F removes the polycaprolactone polymer from the object and turns it opaque. After cooling, a third heating step, known as sintering, melts the silica particles together at temperatures topping 2,300 F to convert the object into clear glass with a smooth, non-layered texture. Achieving that full transparency turned out to be the project's biggest challenge. Including more polymer in the mix made the objects easier to fold but reduced their final transparency, explains Xu, who is presenting the work at the meeting. She ultimately found the right concentrations of polymer and silica to successfully compromise between those competing priorities.

In her latest work, Xu is extending the method beyond glass to ceramics, replacing the silica with substances such as zirconium dioxide and titanium dioxide. Whereas glass is brittle and inert, these compounds open up the possibility of producing "functional" objects, such as materials that are less fragile than glass or that have catalytic properties.

The group is also experimenting with a combination of kirigami and 3D printing to make even more complex shapes. "When you fold a piece of paper, the level of complexity is somewhat limited, and 3D printing is kind of slow," Xie says. "So we wanted to see if we could combine these two techniques to take advantage of their attractive attributes. That would give us the freedom to make almost any shaped part."

In the catalyst field, Xie notes, people use 3D printing to make ceramic structures perforated with microscopic channels, which increase a catalyst's exposed surface area. Xu's method could enable more intricate designs for such applications, and as a test case, she has printed a pierced 3D lattice made of the silica-polymer composite (red structure in accompanying image).

Xu notes that her process could be automated for large-scale manufacturing. She and Xie hope the ceramics and artistic communities will learn about the work and apply it in catalyst and sculpture design, as well as other purposes the researchers haven't even thought of yet.

The researchers acknowledge support and funding from the National Natural Science Foundation of China.