{"id":8117,"date":"2016-03-24T08:33:52","date_gmt":"2016-03-24T08:33:52","guid":{"rendered":"http:\/\/revoscience.com\/en\/?p=8117"},"modified":"2016-03-24T08:33:52","modified_gmt":"2016-03-24T08:33:52","slug":"making-molecules-comfy-ultimate-challenge-for-uws-glass-guy","status":"publish","type":"post","link":"https:\/\/www.revoscience.com\/en\/making-molecules-comfy-ultimate-challenge-for-uws-glass-guy\/","title":{"rendered":"Making molecules comfy: Ultimate challenge for UW\u2019s \u2018Glass Guy\u2019"},"content":{"rendered":"
\"Mark<\/a>
Mark Ediger, professor of chemistry, makes organic glasses in this vacuum
apparatus. PHOTO: DAVID TENENBAUM<\/figcaption><\/figure>\n

\u201cGlass seems to work pretty well,\u201d says glass expert\u00a0Mark Ediger<\/span><\/a>, gesturing at windows overlooking the UW\u2013Madison power plant on Dayton Street. They are the only obvious bit of glass in his office, and so the discussion of 21st century glass entails repeated references toward windows that, ironically, are exactly the kind of glass that doesn\u2019t much interest him.<\/span><\/p>\n

\u201cIf you ask an ordinary person, \u2018What is glass?\u2019 they will point to a window, but glass is a much broader category of materials,\u201d says Ediger, a UW\u2013Madison professor of chemistry. \u201cA plastic ruler is a polymer glass. The fuselage of the Boeing 787 aircraft is a polymer glass reinforced with carbon fiber. And the display of a Samsung smartphone is made of OLEDs (organic light-emitting diodes) that utilize organic glasses.\u201d<\/span><\/p>\n

Scientifically, glass is a non-crystalline, solid material built of molecules or atoms packed together in countless different arrangements.\u00a0 Crystals only tolerate one packing arrangement between neighbors.For 30 years Ediger has been exploring the fundamental properties of organic glass while inventing ways to control the placement of molecules and slow the degradation of a substance that does not have the rigidity of a crystal.<\/span><\/p>\n

\"Sample<\/a>
Sample of organic glass, made in Ediger\u2019s lab<\/figcaption><\/figure>\n

As Ediger positions himself in the window\u2019s sunlight, he explains that the science of \u201csilicate\u201d glass \u2014 the stuff of light bulbs, beer bottles and windows and made largely from sand \u2014 is already highly advanced.<\/span><\/p>\n

Many other glasses, however, exist at the cutting edge of modern science. The glasses that interest Ediger, for example, are made from organic molecules \u2014 compounds based on carbon, the element at the heart of the most diverse assemblage of molecules in the universe.<\/span><\/p>\n

Glasses are more versatile than crystals, Ediger says. \u201cFor any given organic molecule, you only have a few crystal structures to pick from; you are out of luck if one of them does not have the properties you want. But molecules in glass are really flexible about their local environment and who they are willing to hang out with, so for organic molecules, there are an infinite number of glasses we can make. Some glasses might, for example, resist water uptake or be exceptionally hard or resist degradation by light.\u201d<\/span><\/p>\n

As in most glasses, the light-making molecules in an OLED are oriented more or less at random, \u201cbut you want those molecules positioned so the light is aimed toward your eye,\u201d he says. Advanced production techniques to control the orientation of OLED molecules would increase efficiency and extend cellphone battery life. The slight but continual movement of molecules in glass will eventually degrade performance in the hundred-million-odd OLEDs made to illuminate cellphone displays every year; more stable glasses would extend the display lifetime.<\/span><\/p>\n

Ediger acknowledges that this sounds like taming a rebellious group of molecules. \u201cIf we tame them completely, we get a crystal, which we don\u2019t want, but we have found a middle way to produce materials that are in many respects better than traditional glass, but are not crystals.\u201d<\/span><\/p>\n

[pullquote]Ediger eventually figured out that the cold-plate deposition process allowed the molecules to settle into a \u201ccomfortable\u201d position, \u201cand then get buried by another molecule\u201d that locked them in place.[\/pullquote]<\/p>\n

Crystals have their uses \u2014 the silicon crystal is the basis for computer chips, for example \u2014 but glass is better if you want to see through a window or use light for digital communication. \u201cAn optical fiber has to be able to carry a signal what \u2014 60 miles \u2014 without being scattered by the boundaries between crystals,\u201d Ediger says. \u201cThere\u2019s no way you could do that with crystals.\u201d<\/span><\/p>\n

In 2007, in the journal Science, Ediger and colleagues published a key advance in the quest for a middle ground between the rigid repetition of a crystal and the amorphous anarchy of a glass. The article described organic glass made by depositing a vapor of organic molecules on a cold plate in a vacuum chamber. \u201cInitially we did not know what we were making, we just knew that it was bizarre, unexpected,\u201d he says.<\/span><\/p>\n

Ediger had stumbled upon a way to \u201cpre-age\u201d glass and sidestep the seemingly inevitable degradation caused by slight atomic rearrangements over time. \u201cOur contribution was showing that there is this interesting space between traditional glass and crystals,\u201d he says. \u201cYou are putting order in, but if you put in too much order, it becomes a crystal, and you have gone too far.\u201dThe new material did not behave as expected under neutron irradiation. \u201cWe raised the temperature to something we figured would start the molecules moving, but we had to raise the temperature another 25 degrees (Celsius) before the molecules started to move. It turned out we had made a form of glass in which the molecules were so much better packed that they did not move until we reached a much higher temperature.\u201d<\/span><\/p>\n

Ediger eventually figured out that the cold-plate deposition process allowed the molecules to settle into a \u201ccomfortable\u201d position, \u201cand then get buried by another molecule\u201d that locked them in place.<\/span><\/p>\n

\"Yue<\/a>
Yue Qiu, a graduate student of Mark Ediger.<\/figcaption><\/figure>\n

The technique is comparable to the instant production of an ancient vintage of wine, he explains. \u201cThese materials are effectively thousands or millions of years old. They have already had a chance to find a packing arrangement they are pretty happy with, and will stay there for a very long time.\u201d<\/span><\/p>\n

Ediger, a Kansas native, says he started on his quest to instill some rhyme and reason in an amorphous material as a graduate student at Stanford. \u201cGlass was the control for an experiment I was doing. Glass was supposed to be boring and stable, but I was surprised at how much the molecules were rattling around.\u201d<\/span><\/p>\n

Ediger describes himself as \u201ca practical person,\u201d and explains that his theoretical goal is understanding the rules that govern the formation and inevitable transformation of glass over time.Ediger\u2019s fascination with glass grew when Pat Hyde, his first UW\u2013Madison graduate student, \u201cpointed out that we could do experiments to understand glass in a new way. In one way or another, that conversation has been responsible for at least half of what I\u2019ve done at UW\u2013Madison. At a great university you have bright, interesting young people who have good ideas, and they can move science in a direction it would not otherwise go.\u201d<\/span><\/p>\n

The cross-pollination between theory and practicalities continues in Ediger\u2019s lab, as graduate student Yue Qiu uses vacuum deposition to prepare a new set of compounds that could be useful for OLEDs. \u201cYue\u2019s work answers a fundamental question and also can be useful in practice,\u201d Ediger says. \u201cOLEDs deteriorate over time, so cellphone displays get dimmer, and Yue\u2019s work might eliminate that.\u201d<\/span><\/p>\n

Qiu \u201cis also asking an important fundamental question that applies very broadly to many aspects of glass technology,\u201d Ediger says. \u201cHow do you pack the molecules in a glass so tightly that light cannot cause the molecules to rearrange? You could improve cellphone displays by trial and error, but that would be a long process. If we can identify the principles, we could cut years from that.\u201d<\/span><\/p>\n

\u00a0<\/span><\/p>\n","protected":false},"excerpt":{"rendered":"

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