Paint-on plastic electronics: Aligning polymers for high performance

Public release date: 24-Mar-2013
[ | E-mail | Share ]

Contact: Nicole Casal Moore
ncmoore@umich.edu
734-647-7087
University of Michigan

ANN ARBORSemiconducting polymers are an unruly bunch, but University of Michigan engineers have developed a new method for getting them in line that could pave the way for cheaper, greener, "paint-on" plastic electronics.

"This is for the first time a thin-layer, conducting, highly aligned film for high-performance, paintable, directly writeable plastic electronics," said Jinsang Kim, U-M professor of materials science and engineering, who led the research published in Nature Materials.

Semiconductors are the key ingredient for computer processors, solar cells and LED displays, but they are expensive. Inorganic semiconductors like silicon require high temperatures in excess of 2,000 degrees Fahrenheit and costly vacuum systems for processing into electronics, but organic and plastic semiconductors can be prepared on a basic lab bench.

The trouble is that charge carriers, like electrons, can't move through plastics nearly as easily as they can move through inorganic semiconductors, Kim said. Part of the reason for this is because each semiconducting polymer molecule is like a short wire, and these wires are randomly arranged.

"Charge mobility along the polymer chains is much faster than between the polymers," Kim said.

To take advantage of the good conduction along the polymers, research groups have been trying to align them into a charge-carrying freeway, but it's a bit like trying to arrange nanoscopic linguine.

Kim's group approached the problem by making smarter semiconducting polymers. They wanted a liquid polymer solution they could brush over a surface, and the molecules would automatically align with one another in the direction of the stroke, assembling into high-performance semiconducting thin-layer films.

First, they designed the polymers to be slipperyordinary polymers glom together like flat noodles left in the fridge, Kim said. By choosing polymers with a natural twist, the team kept them from sticking to one another in the solution. But in order to align during the brushstroke, the polymers needed to subtly attract one another. Flat surfaces would do that, so the team designed their polymer to untwist as the solvent dried up.

They stopped the unaligned polymers from forming large chunks by adding flexible arms that extended off to the sides of the flat, wire-like polymer. These arms prevented too much close contact among the polymers while the bulkiness of the arms kept them from snagging on one another. Polymers with these properties will line up in the direction of an applied force, such as the tug of a paintbrush.

"It's a big breakthrough," Kim said. "We established a complete molecular design principle of semiconducting polymers with directed alignment capability."

And it works. The team made molecules that matched their design and built a device for spreading the polymer solution over surfaces such as glass or a flexible plastic film. The force from the silicon blade, moving at a constant speed across the liquid polymer, was enough to align the molecules.

The team then built the semiconducting film into a simple transistor, a version of the electronic components that make up computer processors. The device demonstrated the importance of the polymer alignment by showing that charge carriers moved 1,000 times faster in the direction parallel to the silicon blade's brushstroke than they did when crossing the direction of the stroke.

"By combining the established molecular design principle with a polymer that has a very good intrinsic charge carrier mobility, we believe it will make a huge difference in organic electronics," he said. "We are currently developing a versatile fabrication method in order to realize high-performance and paintable plastic electronics in various length scales from nanometers to meters."

Kim believes that the technique will work equally well with atomic-scale pen nibs or large trowel-like applicators for making electronics of all sizes such as LED displays or light-absorbing coatings for solar cells.

The paper is titled "A molecular design principle of lyotropic liquid-crystalline conjugated polymers with directed alignment capability for plastic electronics."

###

The work is funded by the U.S. Department of Energy. Two authors of the paper were partly supported by National Science Foundation and WCU program of National Research Foundation of Korea. The university is pursuing patent protection for the intellectual property and is seeking commercialization partners to help bring the technology to market.

Jinsang Kim's group: http://www.mse.engin.umich.edu/people/jinsang

---

[ | E-mail | Share ]

?

AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert! system.

Public release date: 24-Mar-2013
[ | E-mail | Share ]

Contact: Nicole Casal Moore
ncmoore@umich.edu
734-647-7087
University of Michigan

ANN ARBORSemiconducting polymers are an unruly bunch, but University of Michigan engineers have developed a new method for getting them in line that could pave the way for cheaper, greener, "paint-on" plastic electronics.

"This is for the first time a thin-layer, conducting, highly aligned film for high-performance, paintable, directly writeable plastic electronics," said Jinsang Kim, U-M professor of materials science and engineering, who led the research published in Nature Materials.

Semiconductors are the key ingredient for computer processors, solar cells and LED displays, but they are expensive. Inorganic semiconductors like silicon require high temperatures in excess of 2,000 degrees Fahrenheit and costly vacuum systems for processing into electronics, but organic and plastic semiconductors can be prepared on a basic lab bench.

The trouble is that charge carriers, like electrons, can't move through plastics nearly as easily as they can move through inorganic semiconductors, Kim said. Part of the reason for this is because each semiconducting polymer molecule is like a short wire, and these wires are randomly arranged.

"Charge mobility along the polymer chains is much faster than between the polymers," Kim said.

To take advantage of the good conduction along the polymers, research groups have been trying to align them into a charge-carrying freeway, but it's a bit like trying to arrange nanoscopic linguine.

Kim's group approached the problem by making smarter semiconducting polymers. They wanted a liquid polymer solution they could brush over a surface, and the molecules would automatically align with one another in the direction of the stroke, assembling into high-performance semiconducting thin-layer films.

First, they designed the polymers to be slipperyordinary polymers glom together like flat noodles left in the fridge, Kim said. By choosing polymers with a natural twist, the team kept them from sticking to one another in the solution. But in order to align during the brushstroke, the polymers needed to subtly attract one another. Flat surfaces would do that, so the team designed their polymer to untwist as the solvent dried up.

They stopped the unaligned polymers from forming large chunks by adding flexible arms that extended off to the sides of the flat, wire-like polymer. These arms prevented too much close contact among the polymers while the bulkiness of the arms kept them from snagging on one another. Polymers with these properties will line up in the direction of an applied force, such as the tug of a paintbrush.

"It's a big breakthrough," Kim said. "We established a complete molecular design principle of semiconducting polymers with directed alignment capability."

And it works. The team made molecules that matched their design and built a device for spreading the polymer solution over surfaces such as glass or a flexible plastic film. The force from the silicon blade, moving at a constant speed across the liquid polymer, was enough to align the molecules.

The team then built the semiconducting film into a simple transistor, a version of the electronic components that make up computer processors. The device demonstrated the importance of the polymer alignment by showing that charge carriers moved 1,000 times faster in the direction parallel to the silicon blade's brushstroke than they did when crossing the direction of the stroke.

"By combining the established molecular design principle with a polymer that has a very good intrinsic charge carrier mobility, we believe it will make a huge difference in organic electronics," he said. "We are currently developing a versatile fabrication method in order to realize high-performance and paintable plastic electronics in various length scales from nanometers to meters."

Kim believes that the technique will work equally well with atomic-scale pen nibs or large trowel-like applicators for making electronics of all sizes such as LED displays or light-absorbing coatings for solar cells.

The paper is titled "A molecular design principle of lyotropic liquid-crystalline conjugated polymers with directed alignment capability for plastic electronics."

###

The work is funded by the U.S. Department of Energy. Two authors of the paper were partly supported by National Science Foundation and WCU program of National Research Foundation of Korea. The university is pursuing patent protection for the intellectual property and is seeking commercialization partners to help bring the technology to market.

Jinsang Kim's group: http://www.mse.engin.umich.edu/people/jinsang

---

[ | E-mail | Share ]

?

AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert! system.

Source: http://www.eurekalert.org/pub_releases/2013-03/uom-ppe032013.php

bob costas bowl projections Jovan Belcher Charlie Batch Miguel Calero Bret Bielema

Would Hagel at Defense make war with Iran more likely?

Republican former Sen. Chuck Hagel testifies before a Senate committee in January. (J. Scott Applewhite/AP)Would Defense Secretary Chuck Hagel help set the stage for a war with Iran? Or would the Republican former senator, who seems on track to be confirmed late this month, put the brakes on a possible military confrontation with Tehran over its nuclear program?

The answer -- to both questions -- is yes, some veteran observers of U.S. foreign policy say.

It's a question that reaches far beyond speculative inside-the-Beltway parlor games. There are signs that President Barack Obama?s second-term foreign policy and national security team?and his recent signals to Iran?are part of a final push on the diplomatic front before using military force.

The theory runs something like this: Secretary of State John Kerry is a staunch believer in diplomatic engagement. Hagel has repeatedly expressed deep skepticism about the effectiveness of war with Iran (he even opposed unilateral economic sanctions a decade ago). Both voted in favor of war with Iraq, then turned sharply critical of the conflict. Both men, decorated Vietnam War veterans, aren't likely to rush the country into another overseas occupation.

"These are exactly the people who could make an assault on [Iran] politically sellable," explains Hussein Ibish, a senior fellow at the American Task Force on Palestine. "They may be the smiley face painted on the tip of a bunker-buster."

Ibish said Obama is purposely assembling a team positioned to say two things simultaneously to the Iranian government.

?One is ?We want to make a deal with you, and you will get the best deal out of us that you?ll ever get from any U.S. administration, so take it,'" Ibish told Yahoo News. ?And two, 'If you don?t take it and you cross the red line, you?ll face military action by a group of people who are also in a perfect position to lead the world into a conflict without being vulnerable to the charges of recklessness or warmongering.'"

Ibish may have pioneered the theory, but it can also be heard among influential lawmakers.

Tennessee Sen. Bob Corker, the top Republican on the Senate Foreign Relations Committee, recently told Yahoo News he believes the Obama administration's diplomatic outreach may be laying the groundwork in the event that talks fail.

"The more we are out there diplomatically, doing everything we can to, in a rational way, negotiate with the Iranians, I do think we are building world support should something else have to occur," Corker said.

Vice President Joe Biden, in remarks at an international security conference in Germany, recently offered Iran direct talks. Tehran refused.

"They (the Obama administration) seem like they are checking the boxes of diplomacy," said one foreign policy analyst, who requested anonymity to offer a candid appraisal of that offer.

Hawkish Republicans opposed to confirming Hagel don't see it that way.

GOP senators led by John McCain of Arizona have repeatedly and forcefully denounced their former colleague as insufficiently tough on Iran?casting him as a defense secretary who might gaze on impotently while the Islamic republic develops an atomic arsenal. They've pointed to Hagel's criticisms of imposing unilateral economic sanctions a decade ago, as well as his open skepticism of the effectiveness of military action.

"Can we expect Sen. Hagel to advance and support policies to prevent Iran from gaining a nuclear weapons capability when he has opposed economic sanctions and military intervention?" said McCain, one of his party's top voices on national security.

McCain also dinged Hagel for saying in his confirmation hearing that he backed "containment" of a nuclear Iran?an apparent slip of the tongue on Hagel's part later corrected by the panel's chairman, Democratic Sen. Carl Levin.

?Sen. Hagel?s opposition to the use of sanctions; his apparent confusion about administration policy and its implications; and his apparent incomprehension of the threat a nuclear-armed Iran poses to international stability is alarming and would cause other nations to doubt the credibility of the president?s commitments," McCain charged.

At the White House, officials note that Obama has repeatedly said he won't shy away from using force to prevent Iran from having a nuclear weapon, even though he wants to exhaust diplomatic efforts first. The Democratic president has even embraced the diplo-speak phrase "all options are on the table" that refers to going to war.

?This president has shown time and again that he means what he says?on Iraq, on Afghanistan, on Osama bin Laden,? said National Security Council spokesman Tommy Vietor. ?Republicans should look over here and realize that's true on Iran.?

That may be the biggest problem with the notion that Hagel, or even Kerry, will have a decisive impact on foreign policy.

"It doesn?t matter what John Kerry thinks about Iran. It doens't matter what Chuck Hagel thinks about Iran," said Aaron David Miller, a Middle East expert who has served in Republican and Democratic administrations. "This president has no intention of being the president on whose watch Iran either acquires the capacity to produce a nuclear weapon or a weapon itself."

Obama may successfully cut a diplomatic deal in which Iran bows to demands to halt its uranium enrichment in return for some concessions, perhaps an easing of crippling economic sanctions, said Miller, a vice president at the Wilson Center.

Or, "with great reluctance and some trepidation, the president will use military force" that may not end Iran's nuclear program, Miller said.

"He will accept a messy conclusion, plunging stock markets, inflated oil prices and more regional instability, rather than be the potted plant of American power on this particular question," Miller said. "So Kerry and Hagel may be helpers in that enterprise, but they will not be shapers of it."

Source: http://news.yahoo.com/blogs/ticket/hagel-confirmation-war-iran-more-likely-205057684--politics.html

rose parade