A team of researchers from Texas A&M University and Yonsei University have recently discovered a helicoidal-shaped defect in a layer of polyols that can cause color changes.
Science Advances published this research.
Some human-interactive electronics, such as temperature gauge or health sensor, use polymers that are capable of changing color. This phenomenon is referred to as stimuli-interactive structural colors because the material reacts and changes color due to environmental changes, such as a solvent or solution.
A material with a one-dimensional periodic structure consisting of two layers can reflect light of a given wavelength depending on the thickness of each layer. Stimuli-interactive structural color works by using external stimuli or forces. If all the layers are the same thickness, a single color will be reflected. The material will appear like a normal metal material if different parts of the material are composed of stacks of layers.
In some cases, a preferential solvent is used to swell one of the particular layers, causing color changes. The expected layers were swelling. It was not clear how the solvent was crossing through layers that did not swell to those that were supposed to.
The first A layer swells, the B layer doesn't swell, but the next layer A will. The second layer of solvent A goes through the B layer. We realized there must be something in the overall structure that allows solvent to pass through the other layers.
The researchers used an electron beam to create a tomogram, a reconstruction technique that takes very thin, two-dimensional images of sections of 3D objects to uncover what is inside.
If you sliced it thin, you would eventually hit the hole. The hole would disappear when you kept slicing. You could see where the holes were if you looked at all the slices. This process is similar to a tomograph.
The researchers found that the helicoidal screw dislocations allowed the solvent to easily and rapidly cross through different layers, causing the swelling and producing the stimuli-interactive structural color changes.
Defects are associated with high energy and can disrupt the periodicity in one location. The helicoidal defects are an advantage for the materials.
This is a good kind of defect that helps properties and allows swift and efficient penetration into the material with solvent and rapid swelling. The only way the layers could sweat was from the edges.
Because stimuli-interactive structural color presents an excellent potential for devices such as health sensors and human-interactive electronics, controlling the helicoidal defects could be a critical factor in future applications.
He said that the defects currently produce a favorable effect, but it depends on the application. Increasing the number of applications this technology can be used in is dependent on understanding the defects.
More information: Han Sol Kang et al, Visualization of nonsingular defect enabling rapid control of structural color, Science Advances (2022). DOI: 10.1126/sciadv.abm5120 Journal information: Science Advances Citation: A good defect? Researchers discover helicoidal screw dislocations in layered polymers (2022, May 24) retrieved 24 May 2022 from https://phys.org/news/2022-05-good-defect-helicoidal-dislocations-layered.html This document is subject to copyright. Apart from any fair dealing for the purpose of private study or research, no part may be reproduced without the written permission. The content is provided for information purposes only.
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