microscopyHAADF-S/TEM imaging of aqueous Poloxamer gal-based nanocomposites with the fluid cell in situ. Left: Nanoparticles as small as ~6 nm are clearly seen in a surrounding thick gel matrix. Right: Intensity line scan of a random single particle dispersed in gel. SNR=5 corresponds to the Rose criteria threshold for visibility of nanoparticlesCredit: Ames Lab

Scientists at the U.S. Department of Energy's Ames Laboratory have developed a new microscopy approach for imaging gel nanocomposites in their natural state, which will reveal more useful information about their assembly and properties.

Researchers are excited about imaging nanoparticles in poloxamers, a group of oddly-behaving polymer materials that are liquid at low temperature and a gel at higher temperatures. Because of their interesting phase behavior, these gels show promise in potentially acting as a matrix medium for arrangement of nanoparticles within these gels to obtain materials with interesting optical properties. However, currently, it is very difficult to image nanoparticles within a gel environment.

Like the old idiom "nailing jelly to a wall," getting a close and accurate look at how these nanoparticle-and-gel systems organized themselves has proven difficult for scientists who want to learn more about their properties and how to control them.

"It's basically a goo. It's like honey when cold, and at warmer temperatures it sets into a something like Jello," said Tanya Prozorov, a scientist in Ames Laboratory's Division of Materials Sciences and Engineering. "It's a state of matter that doesn't lend itself well to the thin samples we use in TEM (transmission electron microscopy). Attempting to look at freeze-dried, thin-layer samples of the gel isn't ideal; valuable information gets lost."

Using a new approach with fluid cell scanning/transmission electron microscopy, Prozorov and her colleagues used a molecular printer to deposit miniscule (femtoliter, one quadrillionth of a liter) volumes of poloxamer combined with gold nanoparticles, and observe them under controlled temperature and humidity.