Photonic Sunflower

Photonic product in the shape of a flower can move in response to light, closely tracking the angle of maximum direct exposure. Credit: Fio Omenetto, Tufts University

Technology paves method for intelligent solar batteries, other extremely effective gadgets configured at the macro and nano scale.

Researchers at Tufts University School of Engineering have developed light-activated composite gadgets able to execute accurate, visible motions and form complicated three-dimensional shapes without the need for wires or other actuating materials or energy sources. The design integrates programmable photonic crystals with an elastomeric composite that can be crafted at the macro and nano scale to react to lighting.

The research study offers brand-new avenues for the development of clever light-driven systems such as high-efficiency, self-aligning solar batteries that automatically follow the sun’s instructions and angle of light, light-actuated microfluidic valves or soft robots that move with light on demand. A “photonic sunflower,” whose petals curl towards and far from illumination and which tracks the course and angle of the light, shows the technology in a paper that appears today (March 12 th, 2021) in Nature Communications

Color arises from the absorption and reflection of light. Behind every flash of a rainbowlike butterfly wing or opal gemstone lie complex interactions in which natural photonic crystals embedded in the wing or stone soak up light of specific frequencies and show others. The angle at which the light fulfills the crystalline surface can impact which wavelengths are absorbed and the heat that is created from that taken in energy.

A solar battery mounted on the light actuated product can move and track a source of light without wires, equipments or motors. Credit: Fio Omenetto, Tufts University

The photonic product developed by the Tufts team signs up with two layers: an opal-like film made from silk fibroin doped with gold nanoparticles (AuNPs), forming photonic crystals, and an underlying substrate of polydimethylsiloxane (PDMS), a silicon-based polymer. In addition to amazing flexibility, durability, and optical properties, silk fibroin is unusual in having an unfavorable coefficient of thermal expansion (CTE), suggesting that it contracts when warmed and expands when cooled. PDMS, on the other hand, has a high CTE and expands rapidly when heated up. As a result, when the novel product is exposed to light, one layer heats up a lot more quickly than the other, so the material bends as one side expands and the other contracts or broadens more gradually.

” With our technique, we can pattern these opal-like films at multiple scales to develop the method they soak up and reflect light. When the light relocations and the amount of energy that’s soaked up changes, the product folds and moves in a different way as a function of its relative position to that light,” said Fiorenzo Omenetto, corresponding author of the study and the Frank C. Doble Professor of Engineering at Tufts.

Whereas a lot of optomechanical devices that transform light to movement include complex and energy-intensive fabrication or setups, “We are able to attain elegant control of light-energy conversion and create ‘macro motion’ of these products without the need for any electrical power or wires,” Omenetto said.

The researchers configured the photonic crystal movies by applying stencils and then exposing them to water vapor to create specific patterns. The pattern of surface area water modified the wavelength of absorbed and shown light from the movie, thus triggering the material to flex, fold and twist in various ways, depending upon the geometry of the pattern, when exposed to laser light.

The authors showed in their research study a “photonic sunflower,” with incorporated solar batteries in the bilayer film so that the cells tracked the light. The photonic sunflower kept the angle between the solar cells and the laser beam nearly consistent, making the most of the cells’ efficiency as the light moved. The system would work as well with white light as it does with laser light. Such wireless, light-responsive, heliotropic (sun-following) systems might potentially enhance light-to-energy conversion efficiency for the solar power market. The team’s presentations of the product also included a butterfly whose wings opened and closed in action to light and a self-folding box.

Reference: 12 March 2021, Nature Communications
DOI: 10.1038/ s41467-021-21764 -6

Financing: Office of Naval Research Study

The research study extends ongoing research studies by Omenetto and associates at Tufts School of Engineering on using silk as an advanced material platform in photonics, electronic devices, and nanotechnology.


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