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Managing Editor  | July 2017

Two methods developed for creating self-actuating materials


Researchers at the Institute of Science and Technology (IST) in Klosterneuburg, Austria and at the University of Wisconsin-Milwaukee have developed two very different methods for programming materials to self-actuate and turn from sheets into complex structures.

 

curveups_600

Curve-Ups from IST Austria start as flat sheets and self-actuate into complex shapes.
(IST Austria/YouTube)

 

According to a report from Wiley, which published the final research, the UW-Milwaukee researchers have found a way of chemically programming Nafion foil so that heat causes it to fold into 3-D forms. The foil also remembers its shape. When it is stretched out, it returns to the original shape.

 

The report explained, “Nafion can be protonated in an acidic environment and deprotonated in a basic one. When protonated, stretched Nafion shrinks at temperatures over 100°C, when deprotonated it must be heated over 260°C. As long as the temperature remains within this range, only regions of the Nafion that are protonated will shrink. The deprotonated Nafion is ‘locked’ and does not shrink.”

 

Researchers locked a foil using potassium hydroxide and painted a pattern with hydrochloric acid. As the foil is heated above 100°C, the sheet shrinks and fold along the hydrochloric acid lines.

 

“The scientists made some simple and some complex structures, such as a bird and a zigzag rip pattern common in technical practice; solar panels for satellites, for example, are transported in a folded way and can be spread in just one movement,” the report added. “Simple acid–base chemistry and heating ‘erased’ the structures and the nafion sheets could be coded and folded in a new fashion.”

 

The research was recently published in Angewandte Chemie. Its abstract stated:

 

“Origami- and kirigami-based design principles have recently received strong interest from the scientific and engineering communities because they offer fresh approaches to engineering of structural hierarchy and adaptive functions in materials, which could lead to many promising applications.

 

“Herein, we present a reprogrammable 3D chemical shaping strategy for creating a wide variety of stable complex origami and kirigami structures autonomously. This strategy relies on a reverse patterning method that encodes prescribed 3D geometric information as a spatial pattern of the unlocked phase (dispersed phase) in the locked phase (matrix phase) in a pre-stretched Nafion sheet.

 

“Building upon the unique chemical reprogramming capability of the Nafion shape memory polymer, we have developed a reconfigurable molding technology that can significantly reduce time, costs, and waste by shaping various 3D materials with high fidelity.”

 

In Austria, researchers have created smooth, free-form objects called “Curve-Ups” that self-actuate into a desired shape, according to a report on the IST Austria website.

 

The article explained, “CurveUps are made up of tiny tiles sandwiched between pre-stretched latex layers. During the transformation process, the tension in the latex pulls the tiles together joining them into a continuous shell.”

 

In addition, the researchers can create 2-D tile layouts based on user-supplied 3-D forms with a two-step computer optimization process that first gives an estimated solution and then performs local adjustments to produce the final template. (This process can be seen in action below.)

 

This makes Curve-Ups not only a material breakthrough but also a breakthrough in 3-D printing in manufacturing.

 

The research will be presented at the prestigious SIGGRAPH 2017 conference. The abstract of the report stated:

 

“We present a computational approach for designing CurveUps, curvy shells that form from an initially flat state. They consist of small rigid tiles that are tightly held together by two pre-stretched elastic sheets attached to them.

 

“Our method allows the realization of smooth, doubly curved surfaces that can be fabricated as a flat piece. Once released, the restoring forces of the pre-stretched sheets support the object to take shape in 3D. CurveUps are structurally stable in their target configuration. The design process starts with a target surface. Our method generates a tile layout in 2D and optimizes the distribution, shape, and attachment areas of the tiles to obtain a configuration that is fabricable and in which the curved up state closely matches the target.

 

“Our approach is based on an efficient approximate model and a local optimization strategy for an otherwise intractable nonlinear optimization problem. We demonstrate the effectiveness of our approach for a wide range of shapes, all realized as physical prototypes.”

 

Watch the Curve-Ups process in the video below:

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