Published on September 13th, 2015 | By: April Gocha, PhD0
Inspired by tardigrades: Vapor deposition creates molecular order in glassPublished on September 13th, 2015 | By: April Gocha, PhD
[Image above] A sample, produced at the University of Wisconsin-Madison, that resembles the new ordered glass. Credit: Mark Ediger; University of Wisconsin
Tardigrades are some of the toughest creatures on this planet—these miniscule micro-animals, measuring only about half a millimeter, can survive nearly any condition found on the planet. And beyond the planet, for that matter, since they survive in space.
Part of tardigrades’ intense survival plan is that they form a dehydrated spore-like form (called a tun)—containing ≤3% water—in which the bizarre creatures drop their metabolism down to 0.01% of the normal rate, according to a NY Times article. Dried-out creatures can even be brought back to life after more than a century in desiccation. Indestructible—and all thanks to glass.
“When you remove the water, they very quickly coat themselves in large amounts of glassy molecules,” says Juan de Pablo, Liew Family Professor in Molecular Engineering at the University of Chicago, in a University of Chicago news article. “That’s how they stay in this state of suspended animation.”
Inspired by these strange glass survival houses, de Pablo and his research team have spent the past couple of decades studying similar layers of glassy materials. The work is paying off—this year, the University of Chicago team, in collaboration with researchers in Wisconsin and France, has made of couple of big announcements about its surprising discoveries.
“Randomness is almost the defining feature of glasses,” de Pablo says in the article. “At least we used to think so. What we have done is to demonstrate that one can create glasses where there is some well-defined organization. And now that we understand the origin of such effects, we can try to control that organization by manipulating the way we prepare these glasses.”
To create molecular order, the researchers used vacuum vapor deposition of “large organic moleucles” to build glassy materials layer by layer onto a temperature-controlled substrate.
After growing thin glass films, the team used spectroscopic ellipsometry to measure how light interacted with the material. Those results produced some unexpected anomalies that indicated that the team had manipulated molecular orientation to create order in glassy materials.
The team’s work shows that the order comes from how molecules at the surface of thin layers can interact with air, causing them to align differently than the molecules would align in a bulk liquid.
A University of Chicago news article explains, “The vapor deposition process used in the experiments amounts to laying down one “surface” on top of another. The molecules in each layer get ‘trapped’ in the orientation they had when they were truly, however briefly, on the surface.”
Watch a simulation of deposition on a substrate here. Colored molecules show those with vertical order in the resulting thin film.
Although the amount of molecular order the team can create is small, it is enough to alter the optical properties of the resulting material. The temperature at which the film grows has a big effect on creation of this order, too, so changing the temperature fine-tunes the degree of order in the resulting glass.
The team’s newest results, published in the Journal of Chemical Physics, compared molecular simulation models with those previous experimental results. According to the news article, “the similarities between the data sets are striking.”
This is how science is supposed to work—an interesting result generates a new hypothesis. Additional testing with new techniques and models confirm or refute the hypothesis, and the research adapts to move forward. Theoretical models are an important component to help understand the science behind the observed phenomenon.
“By adding this element of theory, we can actually answer some questions a lot sooner, understand why things happened, and now start designing and engineering materials from first principles because we have a better understanding of how the process works,” de Pablo says in the news article.
Because glasses are a familiar yet still poorly-understood material, this research could help custom design new types of glassy materials with specific properties suited for specific applications. The team also says that the results may help improve efficiency of electronic devices, such as LEDs, optical fibers, and solar cells.
The researchers have patented their method to produce glassy coatings for various applications, including those in pharmaceutical and food industries.
The new paper, published in The Journal of Chemical Physics, is “Orientational anisotropy in simulated vapor-deposited molecular glasses” (DOI: 10.1063/1.4928523).
The previous paper, published in the Proceedings of the National Academy of Sciences of the USA, is “Tunable molecular orientation and elevated thermal stability of vapor-deposited organic semiconductors” (DOI: 10.1073/pnas.1421042112).
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