By Brooke Kuei
Plastics are all around us – they make up our water bottles, trash bags, packing materials, toys, containers, and more. About 300 million tons of plastic are produced worldwide each year, yet the details of what goes on at the atomic scale during the plastics production process is still unclear.
Now, a new technique developed by researchers at Berkeley Lab, in collaboration with Dow and Eindhoven University of Technology in the Netherlands, is providing atomic-resolution details about magnesium chloride, a material involved in the production of the most common plastic, polyethylene – and could help to create a path toward sustainable plastics. Their findings were reported in Advanced Functional Materials.
The researchers used pulsed electron beams in an electron microscope to produce first-of-their-kind images of magnesium chloride. A continuous electron beam rapidly damages this delicate, beam-sensitive material, but the new technique allowed the researchers to study it without harm.
“If you had asked me 10 years ago if we could use pulsed electron beams to image beam-sensitive materials with atomic resolution, I would not have believed it,” said Christian Kisielowski, lead author of the study and staff scientist at the Molecular Foundry. “Now it is possible, and it has allowed us to study an important material for the plastics industry.”
Kisielowski added that this is a game changer for imaging a wide range of materials that are normally damaged inside an electron microscope. Besides magnesium chloride, for example, pulsed electron beams could also be used to study soft membranes and plastics in general.
Although magnesium chloride is widely used as a support structure for catalysts (materials that speed up reactions) used to make plastics, the exact way in which it works remains a mystery. Atomic-scale images of magnesium chloride would help clarify its role in plastics production and could help pave the way to more specialized and sustainable plastics.
Unfortunately, previous attempts at imaging this critical material have been difficult because magnesium chloride can exist in two types of crystal structures that have slightly different arrangements of atoms. “The electron beam itself affects the material structure, making it difficult to interpret which structure is being imaged,” said Kisielowski. “By working with our collaborators, we were able to tease out different interactions.”
The Berkeley Lab team collaborated with Eindhoven University of Technology and Dow to develop a technique that delivers periodic pulses of electrons instead of a continuous electron beam to image magnesium chloride. Using a modified electron microscope at Eindhoven, the researchers found that by pulsing the electron beam like an extremely fast strobe light with one pulse every 160 picoseconds (1 picosecond is one trillionth of a second), the material can essentially “heal” itself between pulses.
