. Nano Technology News .

New Way to Prevent Cracking in Nanoparticle Films
by Staff Writers
Philadelphia PA (SPX) Oct 16, 2012

Nanoparticle films crack at certain thicknesses (left). By adding layers of thinner films, cracking can be avoided (right).

Making uniform coatings is a common engineering challenge, and, when working at the nanoscale, even the tiniest cracks or defects can be a big problem. New research from University of Pennsylvania engineers has shown a new way of avoiding such cracks when depositing thin films of nanoparticles.

The research was led by graduate student Jacob Prosser and assistant professor Daeyeon Lee, both of the Department of Chemical and Biomolecular Engineering in Penn's School of Engineering and Applied Science.

Graduate student Teresa Brugarolas and undergraduate student Steven Lee, also of Chemical and Biomolecular Engineering, and professor Adam Nolte of the Rose-Hulman Institute of Technology participated in the research.

Their work was published in the journal Nano Letters.

To generate a nanoparticle film, the desired particles are suspended in a suitable liquid, which is then thinly and evenly spread over the surface through a variety of physical methods. The liquid is then allowed to evaporate, but, as it dries, the film can crack like mud in the sun.

"One method for preventing cracking is modifying the suspension's chemistry by putting binding additives in there," Prosser said. "But that is essentially adding a new material to the film, which may ruin its properties."

This dilemma is highlighted in the case of electrodes, the contact points in many electrical devices that transfer electricity. High-end devices, like certain types of solar cells, have electrodes composed of nanoparticle films that conduct electrons, but cracks in the films act as insulators. Adding a binder to the films would only compound the problem.

"These binders are usually polymers, which are insulators themselves," Lee said. "If you use them, you're not going to get the targeted property, the conductivity, that you want."

Engineers can prevent cracks with alternative drying methods, but these involve ultra-high temperatures or pressures and thus expensive and complicated equipment. A cheap and efficient method for preventing cracks would be a boon for any number of industrial processes.

The ubiquity of cracking in this context, however, means that researchers know the "critical cracking thickness" for many materials. The breakthrough came when Prosser tried making a film thinner than this threshold, then stacking them together to make a composite of the desired thickness.

"I was thinking about how, in the painting of buildings and homes, multiple coats are used," Prosser said. "One reason for that is to avoid cracking and peeling. I thought it could work for these films as well, so I gave it a try."

"This is one of those things where, once you figure it out," Lee said, "it's so obvious, but somehow this method has evaded everyone all these years."

One reason this approach may have remained untried is that it is counterintuitive that it should work at all.

The method the researchers used to make the films is known as "spin-coating." A precise amount of the nanoparticle suspension - in this case, silica spheres in water - is spread over the target surface.

The surface is then rapidly spun, causing centrifugal acceleration to thin the suspension over the surface in a uniform layer. The suspension then dries with continued rotation, causing the water to evaporate and leaving the silica spheres behind in a compacted arrangement.

But to make a second layer over this first, another drop of liquid suspension would need to be placed on the dried nanoparticles, something that would normally wash them away.

However, the researchers were surprised when the dried layers remained intact after the process was repeated 13 times; the exact mechanism by which they remained stable is something of a mystery.

"We believe that the nanoparticles are staying on the surface," Lee said, "because covalent bonds are being formed between them even though we're not exposing them to high temperatures. The inspiration for that hypothesis came from our colleague Rob Carpick.

"His recent Nature paper was all about how silica-silica surfaces form bonds at room temperature; we think this will work with other kinds of metal oxides."

Future research will be necessary to pin down this mechanism and apply it to new types of nanoparticles.

Related Links
Penn's School of Engineering and Applied Science
Nano Technology News From SpaceMart.com
Computer Chip Architecture, Technology and Manufacture

Get Our Free Newsletters Via Email
Buy Advertising Editorial Enquiries


. Comment on this article via your Facebook, Yahoo, AOL, Hotmail login.

Share this article via these popular social media networks
del.icio.usdel.icio.us DiggDigg RedditReddit GoogleGoogle

Queen's develops new environmentally friendly MOF production method
Belfast, Ireland (SPX) Oct 12, 2012
Chemists at Queen's University Belfast have devised a novel, environmentally friendly technique, which allows the rapid production of Metal-Organic Frameworks porous materials (MOFs). These revolutionary nanomaterials have the potential to transform hazardous gas storage, natural gas vehicles and drug delivery and have the highest surface-area of any known substance. A sugar-lump siz ... read more

Chile deploys Israel's RecceLite system

Quickstep moves on Hercules order

Boeing: Boeing Receives $2 Billion C-17 Aircraft Sustainment Contract

Two flights grounded in China after phone threats: airline

China's manned spacecraft in final preparations for mid-June launch

China launches civilian technology satellites

ChangE-2 Mission To Lagrange L2 Point

Meeting of heads of ESA and China Manned Space Agency

Israel facing increasing number of cyberattacks: PM

US thinks Iran behind cyberattack in Saudi: ex-official

Philippine court suspends cybercrime law

Chinese telecom firms' problems multiply

EU blacklists Iran energy minister under new sanctions

Michigan Energy Markets Poised to Foster Economic Growth and Job Creation

Traditional courtyards: an example of eco-efficiency for architects

Argentine curbs hit Chilean methanol plant

Iran denies sanctions hitting oil sector

Pitt Engineers to Design Affordable CO2 Thickener to Augment Oil Extraction

Sinopec, ENN drop $2.2 bn offer for China Gas

Prestige oil spill disaster trial opens in Spain

Ukraine Brings Back Naval Killer Dolphins

4,000 tonnes of old munitions explode in Russia

Lockheed Martin Completes Centralization Of Targets and Countermeasures Operations in Huntsville

US hails war vehicle that saved lives, bypassed bureaucracy

NASA must reinvest in nanotechnology research, according to new Rice University paper

New Techniques Stretch Carbon Nanotubes, Make Stronger Composites

New Way to Prevent Cracking in Nanoparticle Films

Queen's develops new environmentally friendly MOF production method

NASA's Ironman-Like Exoskeleton Could Give Astronauts, Paraplegics Improved Mobility and Strength

Worldwide patent for a Spanish stroke rehabilitation robot

Robot artist learns masters' brush strokes

Toyota unveils robot helping hand

Memory Foam Mattress Review

Newsletters :: SpaceDaily Express :: SpaceWar Express :: TerraDaily Express :: Energy Daily
XML Feeds :: Space News :: Earth News :: War News :: Solar Energy News


The content herein, unless otherwise known to be public domain, are Copyright 1995-2012 - Space Media Network. AFP, UPI and IANS news wire stories are copyright Agence France-Presse, United Press International and Indo-Asia News Service. ESA Portal Reports are copyright European Space Agency. All NASA sourced material is public domain. Additional copyrights may apply in whole or part to other bona fide parties. Advertising does not imply endorsement,agreement or approval of any opinions, statements or information provided by Space Media Network on any Web page published or hosted by Space Media Network. Privacy Statement