July 3, 2017 report
Making miniature mazes by wrinkling surface of tiny particles
As the researchers note, prior efforts have been made by different teams to create tiny mazes by taking advantage of wrinkling, but until now, there was no order to the resulting mazes, which meant there was little practical use for them. In this new effort, the researchers have found a self-organized way to construct maze-like microstructures that are periodic and ordered but which also have a degree of randomness to them.
To make their mazes, the team used ultraviolet light to etch patterns on a given microparticle—photomasks (tiny plates with holes or slits to allow light to pass through in a pattern) were used to create specific etched patterns. The design on the particle was then coated with silica. As the silica dried, the surface wrinkled naturally, creating ridges that became parts of the maze—bends, for example, or endings, straight lines or splits. The use of the photomasks to create designs on the particles prior to shining the ultraviolet light allowed for controlling the way the parts of the maze arose as the silica wrinkled. The technique also allowed for customizing the overall look of the maze, resulting in perpendicular-shaped, hexagonal or even ring-shaped mazes. The team reports that they were even able to make one maze that had the capital letter N at its center.
The team notes that the mazes could be made without blueprints and that they could be given unique features by adjusting the photomasks, making them ideal candidates to serve as security features. The tiny mazes could serve as what the team calls "physical unclonable functions" offering a physical way to undergird an encryption system with an ID-creating technique baked right into a system, making it virtually impossible for a hacker to gain access.
Sophisticated three-dimensional (3D) structures found in nature are self-organized by bottom-up natural processes. To artificially construct these complex systems, various bottom-up fabrication methods, designed to transform 2D structures into 3D structures, have been developed as alternatives to conventional top-down lithography processes. We present a different self-organization approach, where we construct microstructures with periodic and ordered, but with random architecture, like mazes. For this purpose, we transformed planar surfaces using wrinkling to directly use randomly generated ridges as maze walls. Highly regular maze structures, consisting of several tessellations with customized designs, were fabricated by precisely controlling wrinkling with the ridge-guiding structure, analogous to the creases in origami. The method presented here could have widespread applications in various material systems with multiple length scales.
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