HONG KONG SAR – Media OutReach – September 25, 2023 – Researchers from the University of Hong Kong (HKU) have designed an innovative pixelated soft color changing system called Morphable Concavity Array (MoCA).
(MoCA): a color-changing pixelated software system that mimics the color-changing structure of the butterfly’s wing.
Soft color-changing pixelated systems are malleable structures that, by manipulating light, can change color. They have applications in a wide range of industries, from medical bandages that change color when infected, to foldable smartphone and tablet screens, to wearable technology where sensors are integrated into the clothing fabric.
The research was co-led by Professor Anderson Ho Cheung Shum from the Department of Mechanical Engineering at HKU and Professor Mingzhu Li from the Institute of Chemistry of the Chinese Academy of Sciences, and led by Dr Yi Pan from the Department of Mechanical Engineering from HKU. .
The MoCA made by HKU researchers is a thin (its thickness is about 3 human hairs) rubber-like structure that consists of two layers: the top layer is a photonic crystal elastomer (PC) actuator film -EA) and the bottom layer is a hole. array – a trellis with evenly spaced round holes.
The PC-EA film itself consists of two layers: an elastomer layer (GPDMS) on top and a hydrogel layer (pNIPAM) below.
If ethanol is added to the pNIPAM layer, it swells and the resulting tension pulls the GPDMS elastomer layer down into the lattice hole, producing a concave, dish-like shape called morphable concavity (MoC). ) which acts like a pixel. Once the concavity is formed, the red light is blocked and the visible color of the pixel changes from red to blue.
MoCA was inspired by structures in butterfly wings called bi-color micro-concavities that produce vibrant, irredescent colors.
Two-color microconcavities are tiny pits that block certain wavelengths of light, producing two different colors depending on the angle of the light and the viewer’s perspective. On the wings of butterflies, these hollows are arranged in regular structures called photonic crystals.
MoCA replicates the photonic crystal of the butterfly wing and is revolutionary as the first example of a pixelated color-changing system that relies on flat and concave structures to produce different colors.
“The color-changing strategy of MoCA is achieved by modifying its local morphology, in particular by controlling the transition between ‘flat’ and ‘concave’ states. This distinguishes MoCA from other pixelated color-changing systems,” said Dr. Pan.
Another advancement is that pixel color changes can be manipulated individually, because in MoCA each pixel is connected to an individual “pipe system” through which the ethanol is delivered.
“We use multichannel microfluidics to introduce and remove solvents to manipulate MoCA, providing a complementary approach to conventional electrochromic methods,” explained Dr. Pan.
MoCA can be used for counterfeiting purposes – for example to conceal products such as clothing, designs or QR codes that can only be visible under certain conditions. The HKU team’s long-term goal, however, is to use the principles behind MoCA – soft matter and microfluidics – to build optical devices that mimic and surpass the capabilities of insect compound eyes.
Compound eyes contain multiple light-processing structures and offer several advantages over non-compound vision, such as a wider field of vision and the ability to focus on multiple objects at the same time.
The distortion of the lens of the human eye allows us to focus at different distances, explains Professor Shum. MoCA technology, which allows individual units to be deformed from flat to concave, can be leveraged to create multiple lenses that can change focus individually.
Crystal lenses have their own advantages, such as greater focusing ability, higher resolution and better color perception.
“Optical devices combining the compound eye and the lens would not only mimic nature, but transcend it,” Professor Shum said.
The results were published in
Advanced science as “Reactive structural color pixelated via a bioinspired morphable concavity array (MoCA) composed of 2D photonic crystal elastomer actuators”.
Statement: Use of materials in this article (Yi Pan, Chang Li, Xiaoyu Hou, Zhenyu Yang, Mingzhu Li, Ho Cheung Shum. Responsive structural color pixelization via bioinspired morphable concavity array (MoCA) composed of elastomer actuators 2D photonic crystal.
Advanced science2023, 10, 2300347.) follows the terms of its CC BY 4.0 license (https://creativecommons.org/licenses/by/4.0/) and all materials are used without any modification.
Link to document:
https://onlinelibrary.wiley.com/doi/10.1002/advs.202300347
Hashtag: #HKU
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