This image shows a rendering (gray and pink) of the molecular structure of a peptoid polymer that was studied by a team led by Berkeley Lab and UC Berkeley. The successful imaging of a polymer’s atomic-scale structure could inform new designs for plastics, like those that form the water bottles shown in the background. (Credit: Berkeley Lab, Charles Rondeau/PublicDomainPictures.net)
From water bottles and food containers to toys and tubing, many modern materials are made of plastics. And while we produce about 110 million tons per year of synthetic polymers like polyethylene and polypropylene worldwide for these plastic products, there are still mysteries about polymers at the atomic scale.
Because of the difficulty in capturing images of these materials at tiny scales, images of individual atoms in polymers have only been realized in computer simulations and illustrations, for example.
Now, a research team led by Nitash Balsara, a senior faculty scientist in the Materials Sciences Division at the Department of Energy’s Lawrence Berkeley National Laboratory (Berkeley Lab) and professor of chemical and biomolecular engineering at UC Berkeley, has adapted a powerful electron-based imaging technique to obtain an image of atomic-scale structure in a synthetic polymer. The team included researchers from Berkeley Lab and UC Berkeley.
The research could ultimately inform polymer fabrication methods and lead to new designs for materials and devices that incorporate polymers.
In their study, published in the American Chemical Society’s Macromolecules journal, the researchers detail the development of a cryogenic electron microscopy imaging technique, aided by computerized simulations and sorting techniques, that identified 35 arrangements of crystal structures in a peptoid polymer sample. Peptoids are synthetically produced molecules that mimic biological molecules, including chains of amino acids known as peptides.
The sample was robotically synthesized at Berkeley Lab’s Molecular Foundry, a DOE Office of Science User Facility for nanoscience research. Researchers formed sheets of crystallized polymers measuring about 5 nanometers (billionths of a meter) in thickness when dispersed in water.
“We conducted our experiments on the most perfect polymer molecules we could make,” Balsara said – the peptoid samples in the study were extremely pure compared to typical synthetic polymers.
"Imaging Unstained Synthetic Polymer Crystals and Defects on Atomic Length Scales Using Cryogenic Electron Microscopy", American Chemical Society Macromolecules journal