Tag Archives: rose petal

Printing metal on flowers or gelatin

Martin Thuo and his research group have developed heat-free technology that can print conductive, metallic lines and traces on just about anything, including a rose petal. Photo courtesy of Martin Thuo.

I’m not sure how I feel about an electrified rose but it is strangely fascinating. Here’s more from a July 29, 2019 news item on Nanowerk,

Martin Thuo of Iowa State University and the Ames Laboratory clicked through the photo gallery for one of his research projects.

How about this one? There was a rose with metal traces printed on a delicate petal.

Or this? A curled sheet of paper with a flexible, programmable LED display.

Maybe this? A gelatin cylinder with metal traces printed across the top.

Caption: Martin Thuo and his research group have printed electronic traces on gelatin. Credit: Martin Thuo/Iowa State University

A July 26, 2019 Iowa State University news release (also on EurekAlert but published on July 29, 2019), which originated the news item,

All those photos showed the latest application of undercooled metal technology developed by Thuo and his research group. The technology features liquid metal (in this case Field’s metal, an alloy of bismuth, indium and tin) trapped below its melting point in polished, oxide shells, creating particles about 10 millionths of a meter across.

When the shells are broken – with mechanical pressure or chemical dissolving – the metal inside flows and solidifies, creating a heat-free weld or, in this case, printing conductive, metallic lines and traces on all kinds of materials, everything from a concrete wall to a leaf.

That could have all kinds of applications, including sensors to measure the structural integrity of a building or the growth of crops. The technology was also tested in paper-based remote controls that read changes in electrical currents when the paper is curved. Engineers also tested the technology by making electrical contacts for solar cells and by screen printing conductive lines on gelatin, a model for soft biological tissues, including the brain.

“This work reports heat-free, ambient fabrication of metallic conductive interconnects and traces on all types of substrates,” Thuo and a team of researchers wrote in a paper describing the technology recently published online by the journal Advanced Functional Materials.

Thuo – an assistant professor of materials science and engineering at Iowa State, an associate of the U.S. Department of Energy’s Ames Laboratory and a co-founder of the Ames startup SAFI-Tech Inc. that’s commercializing the liquid-metal particles – is the lead author. Co-authors are Andrew Martin, a former undergraduate in Thuo’s lab and now an Iowa State doctoral student in materials science and engineering; Boyce Chang, a postdoctoral fellow at the University of California, Berkeley, who earned his doctoral degree at Iowa State Zachariah Martin, Dipak Paramanik and Ian Tevis, of SAFI-Tech; Christophe Frankiewicz, a co-founder of Sep-All in Ames and a former Iowa State postdoctoral research associate; and Souvik Kundu, an Iowa State graduate student in electrical and computer engineering.
The project was supported by university startup funds to establish Thuo’s research lab at Iowa State, Thuo’s Black & Veatch faculty fellowship and a National Science Foundation Small Business Innovation Research grant.

Thuo said he launched the project three years ago as a teaching exercise.

“I started this with undergraduate students,” he said. “I thought it would be fun to get students to make something like this. It’s a really beneficial teaching tool because you don’t need to solve 2 million equations to do sophisticated science.”

And once students learned to use a few metal-processing tools, they started solving some of the technical challenges of flexible, metal electronics.

“The students discovered ways of dealing with metal and that blossomed into a million ideas,” Thuo said. “And now we can’t stop.”

And so the researchers have learned how to effectively bond metal traces to everything from water-repelling rose petals to watery gelatin. Based on what they now know, Thuo said it would be easy for them to print metallic traces on ice cubes or biological tissue.

All the experiments “highlight the versatility of this approach,” the researchers wrote in their paper, “allowing a multitude of conductive products to be fabricated without damaging the base material.”

Here’s a link to and a citation for the paper,

Heat‐Free Fabrication of Metallic Interconnects for Flexible/Wearable Devices by Andrew Martin, Boyce S. Chang, Zachariah Martin, Dipak Paramanik, Christophe Frankiewicz, Souvik Kundu, Ian D. Tevis, Martin Thuo. Advanced Functional Materials Online Version of Record before inclusion in an issue 1903687 DOI: https://doi.org/10.1002/adfm.201903687 First published online: 15 July 2019

This paper is behind a paywall.

Photovoltaics as rose petals

Where solar cells (photovoltaics) are concerned, mimimicking plants is a longstanding pursuit. The latest  plant material to be mimicked is the rose petal’s surface. From a June 24, 2016 news item on ScienceDaily,

With a surface resembling that of plants, solar cells improve light-harvesting and thus generate more power. Scientists of KIT (Karlsruhe Institute of Technology) reproduced the epidermal cells of rose petals that have particularly good antireflection properties and integrated the transparent replicas into an organic solar cell. This resulted in a relative efficiency gain of twelve percent. …

Caption: Biomimetics: the epidermis of a rose petal is replicated in a transparent layer which is then integrated into the front of a solar cell. Credit Illustration: Guillaume Gomard, KIT

Caption: Biomimetics: the epidermis of a rose petal is replicated in a transparent layer which is then integrated into the front of a solar cell.
Credit Illustration: Guillaume Gomard, KIT

A June 24, 2016 KIT press release on EurekAlert, which originated the news item, expands on the theme,

Photovoltaics works in a similar way as the photosynthesis of plants. Light energy is absorbed and converted into a different form of energy. In this process, it is important to use a possibly large portion of the sun’s light spectrum and to trap the light from various incidence angles as the angle changes with the sun’s position. Plants have this capability as a result of a long evolution process – reason enough for photovoltaics researchers to look closely at nature when developing solar cells with a broad absorption spectrum and a high incidence angle tolerance.

Scientists at the KIT and the ZSW (Center for Solar Energy and Hydrogen Research Baden-Württemberg) now suggest in their article published in the Advanced Optical Materials journal to replicate the outermost tissue of the petals of higher plants, the so-called epidermis, in a transparent layer and integrate that layer into the front of solar cells in order to increase their efficiency.

First, the researchers at the Light Technology Institute (LTI), the Institute of Microstructure Technology (IMT), the Institute of Applied Physics (APH), and the Zoological Institute (ZOO) of KIT as well as their colleagues from the ZSW investigated the optical properties, and above all, the antireflection effect of the epidermal cells of different plant species. These properties are particularly pronounced in rose petals where they provide stronger color contrasts and thus increase the chance of pollination. As the scientists found out under the electron microscope, the epidermis of rose petals consists of a disorganized arrangement of densely packed microstructures, with additional ribs formed by randomly positioned nanostructures.

In order to exactly replicate the structure of these epidermal cells over a larger area, the scientists transferred it to a mold made of polydimethylsiloxane, a silicon-based polymer, pressed the resulting negative structure into optical glue which was finally left to cure under UV light. “This easy and cost-effective method creates microstructures of a depth and density that are hardly achievable with artificial techniques,” says Dr. Guillaume Gomard, Group Leader “Nanopothonics” at KIT’s LTI.

The scientists then integrated the transparent replica of the rose petal epidermis into an organic solar cell. This resulted in power conversion efficiency gains of twelve percent for vertically incident light. At very shallow incidence angles, the efficiency gain was even higher. The scientists attribute this gain primarily to the excellent omnidirectional antireflection properties of the replicated epidermis that is able to reduce surface reflection to a value below five percent, even for a light incidence angle of nearly 80 degrees. In addition, as examinations using a confocal laser microscope showed, every single replicated epidermal cell works as a microlense. The microlense effect extends the optical path within the solar cell, enhances the light-matter-interaction, and increases the probability that the photons will be absorbed.

“Our method is applicable to both other plant species and other PV technologies,” Guillaume Gomard explains. “Since the surfaces of plants have multifunctional properties, it might be possible in the future to apply multiple of these properties in a single step.” The results of this research lead to another basic question: What is the role of disorganization in complex photonic structures? Further studies are now examining this issue with the perspective that the next generation of solar cells might benefit from their results.

Here’s a link to and a citation for the paper,

Flower Power: Exploiting Plants’ Epidermal Structures for Enhanced Light Harvesting in Thin-Film Solar Cells by Ruben Hünig, Adrian Mertens, Moritz Stephan, Alexander Schulz, Benjamin Richter, Michael Hetterich, Michael Powalla, Uli Lemmer, Alexander Colsmann, and Guillaume Gomard. Advanced Optical Materials  Version of Record online: 30 MAY 2016 DOI: 10.1002/adom.201600046

© 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

This paper is behind a paywall.