Now, researchers will fill in the missing knowledge on nanoscale polymerization and “smart” medicine and environmental materials.
A new microscopy method has been developed by Northwestern researchers that allows scientists to see how at the nanoscale the building blocks of “smart” materials are created.
The chemical process is expected to transform the future of clean water and medications, and humans will be able to see the process in action for the first time.
“Our method allows us to visualize this type of polymerization in real time at the nanoscale, which has never been done before,” says Northwestern’s Nathan Gianneschi. “We now have the ability to see how the reaction occurs, see how these nanostructures are formed, and learn how to exploit the incredible things they can do.”
The report was published in the journal Matter on Dec. 22, 2020.
The study is the result of a collaboration between Gianneschi, Associate Director of the International Institute of Nanotechnology and Professor of Chemistry at the Weinberg College of Arts and Sciences at Jacob and Rosalind Cohn, and Brent Sumerlin, Professor of Polymer Chemistry at the University of Florida College of Liberal Arts and Sciences at George and Josephine Butler.
“It’s like comparing a few photos of a soccer game to the information contained in a video of the entire game.”
—First author, Nathan Gianneschi
Dispersion polymerization, often on an industrial scale, is a common scientific process used to produce medications, cosmetics, latex and other products.
And polymerization can be used at the nanoscale to produce nanoparticles that have special and useful properties.
These nanomaterials hold great promise for the ecosystem, where they can be used without damaging aquatic organisms to soak up oil spills or other contaminants.
In medicine, they can be configured to enter human cells as the basis of “smart” drug delivery systems and release therapeutic molecules under certain conditions.
Difficulties in scaling up production of these materials have been found.
Initially, the time-consuming process needed to build and then trigger them hindered development.
A technique called polymerization-induced self-assembly (PISA) combines the steps and saves time, but it has proven difficult to predict the actions of the molecules during this process for a simple reason: scientists have not been able to observe what actually occurs.
Nanoscale reactions are much too small to be observed by the naked eye.
Only the end product of polymerization can be captured by traditional imaging methods, not the mechanism by which it happens. By taking samples at various points in the process and examining them, scientists have tried to get around this problem, but using only snapshots does not tell the full story of the chemical and physical changes that occur during the process.
Gianneschi says, “It’s like comparing a few photos of a soccer game to the information contained in a video of the entire game,” “If you understand the way a chemical is formed, if you can see how it was formed, then you can learn how to speed it up, and you can figure out how to disrupt the process so you get a different effect.”
Transmission electron microscopy (TEM) is capable of capturing sub-nanometer resolution images, but is usually used for frozen samples and is therefore unable to imagine chemical reactions.
In TEM, an electron beam is shot through a vacuum at the object; a picture can be produced by observing the electrons that come out on the other side. The quality of the picture, however, depends on how many electrons the beam fires – and if you fire too many electrons, it will compromise the chemical reaction result.
In other words, this is a case of the observer effect – it could alter or even harm the self-assembly observation.
What you end up with, if you weren’t watching, is different from what you would have.
The researchers put the nanoscale polymer materials in a closed liquid cell designed to shield the materials in the electron microscope from the vacuum to solve the problem.
These materials have been engineered to react to changes in temperature.