Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Sticky business: Magnetic pollen replicas offer multimodal adhesion

22.11.2013
Researchers have created magnetic replicas of sunflower pollen grains using a wet chemical, layer-by-layer process that applies highly conformal iron oxide coatings.

The replicas possess natural adhesion properties inherited from the spiky pollen particles while gaining magnetic behavior, allowing for tailored adhesion to surfaces.


These scanning electron microscope images show a pollen particle (left) that has been coated with iron oxide and a replica of the same particle (right) after firing at 600 C to remove the organic material and crystallize the iron oxide. Arrows point to features that were preserved by the process.

Credit: Courtesy of Brandon Goodwin and Ken Sandhage

By taking advantage of the native pollen grain shape and a non-natural oxide chemistry, this work provides a unique demonstration of tunable, bio-enabled multimodal adhesion. The spikes inherited from the sunflower pollen provide short range adhesion – over nanoscale distances – while the oxide chemistry provides an adhesion mode that operates over much longer distances – up to one millimeter.

The work was supported by the Air Force Office of Scientific Research, and has been accepted for publication in the journal Chemistry of Materials. A "just-accepted" version of the manuscript has appeared online.

"Pollen grains are inexpensive and sustainable templates that are readily available in large quantities," said Ken Sandhage, a professor in the School of Materials Science and Engineering at the Georgia Institute of Technology. "Because pollen grains are already designed by nature for adhesion, we thought that it would be interesting to try to augment such natural behavior with an additional, non-natural mode of adhesion."

Sandhage and graduate student Brandon Goodwin began by examining the microscopic shapes of several types of pollen – including ragweed, pecan and dandelion – before choosing particles from the sunflower (Helianthus annuus). The sunflower pollen grains are nearly spherical, but covered with spikes that can entangle with the hairs on bees' legs, or adhere to surfaces via van der Waals forces at nanometer-scale distances, Sandhage explained.

The researchers washed the burr-like pollen particles with chloroform, methanol, hydrochloric acid and water to clean the surfaces and expose hydroxyl groups for chemically attaching their coating. They then applied iron oxide using an automated, layer-by-layer surface sol-gel process they had developed earlier for coating diatom shells made of silica. Reaction of the iron oxide precursor with the hydroxyl groups on the surface of the pollen particles resulted in a highly-conformal coatings.

The sol-gel process used alternating cycles of exposure to an iron (III) isopropoxide precursor solution and water to apply 30 thin layers of hematite (Fe2O3) onto the pollen. Heating the particles to 600 degrees Celsius then burned out the organic material from the original pollen grains and crystallized the iron oxide, leaving hollow 3D particles. The shells were then heated again in a controlled oxygen atmosphere to convert the hematite into magnetite (Fe3O4), which is more strongly magnetic.

"We examined individual pollen grains before and after firing, and we could see that the shape and surface features were well preserved," said Sandhage, who is the B. Mifflin Hood Professor in the School of Materials Science and Engineering. "The conformal nature of the coating process allowed us to generate ceramic replicas that retained even tiny surface features on the starting pollen grains."

The adhesion properties of the magnetic pollen-shaped particles were then analyzed by graduate student Ismael Gomez and professor Carson Meredith, both from Georgia Tech's School of Chemical and Biomolecular Engineering. Gomez and Meredith used an atomic force microscope (AFM) tip to press the replicas onto a variety of surfaces, then measured the force required to remove them from the surfaces. They studied replica pollen adhesion to polyvinyl alcohol, polyvinyl acetate, polystyrene, silicon, nickel and neodymium-iron-boron – and compared the adhesion properties to those of the original sunflower pollen grains.

"We found that we achieved multimodal adhesion by retaining short-range van der Waals attraction, as exhibited by the native pollen, and gaining magnetic adhesion," Sandhage said.

The layer-by-layer nature of the coating process allowed for control of the amount of magnetic material, and the magnetic properties of the pollen replicas. The researchers chose to apply 30 layers to achieve sufficient long-range magnetic behavior while retaining high-aspect-ratio, sharp spikes that provide for short-range van der Waals forces.

"Reproducibly generating large quantities of such cheap microparticles possessing high-aspect surface features over their entire particle surfaces would be quite challenging using synthetic top-down methods," Sandhage said.

The Air Force Multidisciplinary University Research Initiative (MURI) that funded the work is aimed at both understanding adhesion in natural systems and controllably tailoring such adhesion. In future research supported by the MURI, Sandhage and Meredith plan to study other oxide materials and explore the variety of shapes available in pollen particles.

"Now that we know how to generate such particle replicas, there is certainly more chemical tailoring that we can explore for adhesion," said Sandhage, who also holds an adjunct position in Georgia Tech's School of Chemistry and Biochemistry. "Through the proper combination of pollen shape, synthetic chemistry and thermal treatments, we can significantly expand the range of properties of these pollen replicas."

This research was supported by the U.S. Air Force Office of Scientific Research through award number FA9550-10-1-0555. Any conclusions are those of the authors and do not necessarily represent the official views of the U.S. Air Force.

CITATION: William Brandon Goodwin, Ismael J. Gomez, Carson Meredith and Kenneth H. Sandhage, "Conversion of Pollen Particles into Three-Dimensional Ceramic Replicas Tailored for Multimodal Adhesion." (Chemistry of Materials, 2013): http://dx.doi.org/10.1021/cm402226w

John Toon | EurekAlert!
Further information:
http://www.gatech.edu

All articles from Materials Sciences >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: Controlling superconducting regions within an exotic metal

Superconductivity has fascinated scientists for many years since it offers the potential to revolutionize current technologies. Materials only become superconductors - meaning that electrons can travel in them with no resistance - at very low temperatures. These days, this unique zero resistance superconductivity is commonly found in a number of technologies, such as magnetic resonance imaging (MRI).

Future technologies, however, will harness the total synchrony of electronic behavior in superconductors - a property called the phase. There is currently a...

Im Focus: How Do the Strongest Magnets in the Universe Form?

How do some neutron stars become the strongest magnets in the Universe? A German-British team of astrophysicists has found a possible answer to the question of how these so-called magnetars form. Researchers from Heidelberg, Garching, and Oxford used large computer simulations to demonstrate how the merger of two stars creates strong magnetic fields. If such stars explode in supernovae, magnetars could result.

How Do the Strongest Magnets in the Universe Form?

Im Focus: Liquifying a rocky exoplanet

A hot, molten Earth would be around 5% larger than its solid counterpart. This is the result of a study led by researchers at the University of Bern. The difference between molten and solid rocky planets is important for the search of Earth-like worlds beyond our Solar System and the understanding of Earth itself.

Rocky exoplanets that are around Earth-size are comparatively small, which makes them incredibly difficult to detect and characterise using telescopes. What...

Im Focus: Axion particle spotted in solid-state crystal

Scientists at the Max Planck Institute for Chemical Physics of Solids in Dresden, Princeton University, the University of Illinois at Urbana-Champaign, and the University of the Chinese Academy of Sciences have spotted a famously elusive particle: The axion – first predicted 42 years ago as an elementary particle in extensions of the standard model of particle physics.

The team found signatures of axion particles composed of Weyl-type electrons (Weyl fermions) in the correlated Weyl semimetal (TaSe₄)₂I. At room temperature,...

Im Focus: A cosmic pretzel

Twin baby stars grow amongst a twisting network of gas and dust

The two baby stars were found in the [BHB2007] 11 system - the youngest member of a small stellar cluster in the Barnard 59 dark nebula, which is part of the...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

VideoLinks
Industry & Economy
Event News

International Symposium on Functional Materials for Electrolysis, Fuel Cells and Metal-Air Batteries

02.10.2019 | Event News

NEXUS 2020: Relationships Between Architecture and Mathematics

02.10.2019 | Event News

Optical Technologies: International Symposium „Future Optics“ in Hannover

19.09.2019 | Event News

 
Latest News

Electrochemistry to benefit photonics: Nanotubes can control laser pulses

11.10.2019 | Physics and Astronomy

Biologically inspired skin improves robots' sensory abilities (Video)

11.10.2019 | Power and Electrical Engineering

New electrolyte stops rapid performance decline of next-generation lithium battery

11.10.2019 | Power and Electrical Engineering

VideoLinks
Science & Research
Overview of more VideoLinks >>>