Jun 12 2019
Plastics can be found everywhere. These materials are used for making containers, toys, water bottles, packing materials, trash bags, and much more.
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. (Image credit: iStock/Irina Vodneva)
Globally, around 300 million tons of plastic are manufactured every year, but the details of what transpires at the atomic scale during the process of plastics production are still not clear.
Now, a research team at DOE’s Lawrence Berkeley National Laboratory (Berkeley Lab), in association with Dow and Eindhoven University of Technology in the Netherlands, has created a novel method that is offering atomic-resolution details of magnesium chloride, a material used in the production of polyethylene, which happens to be the most common plastic. The new method could help in forging a path toward sustainable plastics. The results of the study have been reported in Advanced Functional Materials.
The scientists created first-of-their-kind images of magnesium chloride using pulsed electron beams in an electron microscope. A continuous beam of electrons quickly damages this fragile and beam-responsive material; however, the novel method enabled the team to examine it without any 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. Now it is possible, and it has allowed us to study an important material for the plastics industry.
Christian Kisielowski, Study Lead Author and Staff Scientist, The Molecular Foundry, Lawrence Berkeley National Laboratory
The Molecular Foundry is a nanoscale science user facility.
According to Kisielowski, this is definitely a game changer for imaging an array of materials that are usually damaged within an electron microscope. For instance, in addition to magnesium chloride, pulsed electron beams may also be used for inspecting plastics and soft membranes in general.
Focusing on a new path toward sustainable plastics
Even though magnesium chloride is extensively used as a support structure for catalysts—materials that accelerate reactions—used for making plastics, the precise way in which it works still remains unclear. The role of magnesium chloride in plastics production could be clarified with atomic-scale images. These images could lead to the development of more sustainable and specialized plastics.
However, magnesium chloride can occur in two forms of crystal structures in which atoms are arranged in a slightly different manner, and this made earlier attempts of imaging this critical material quite difficult.
The electron beam itself affects the material structure, making it difficult to interpret which structure is being imaged. By working with our collaborators, we were able to tease out different interactions.
Christian Kisielowski, Study Lead Author and Staff Scientist, The Molecular Foundry, Lawrence Berkeley National Laboratory
The researchers at Berkeley Lab teamed up with Eindhoven University of Technology and Dow to devise a method that transports periodic pulses of electrons and not a continuous electron beam for imaging magnesium chloride.
With the help of a modified electron microscope at Eindhoven, the team discovered that when the electron beam, such as an extremely fast strobe light, is pulsed with a single pulse every 160 picoseconds (1 picosecond is equal to one trillionth of a second), the material can fundamentally “heal” itself between the pulses.
It is well known that samples tend to become damaged in an electron microscope when molecules are divided into tinier particles or atoms are knocked out of position. This study demonstrated to the research team that the build-up of atomic vibrations induced by the electron beam is also significant. Timely pulsing of the electron beam with these vibrations allowed the researchers to maintain the original atomic structure of the material and it also showed that magnesium chloride sheets stack on top of one another in a random arrangement similar to a haphazard stack of books, which distinguishes it from other types of materials.
Another major issue that other investigators have faced when imaging magnesium chloride is that upon exposure to air, the material varies in both crystal structure and chemical content (the way its atoms are organized in space). However, when traditional electron microscopy methods are used, the sample is subjected to air while it is being delivered to the microscope.
When new solutions become crystal clear
Kisielowski observed that through their association with Dow, they successfully lowered the material’s exposure to air before placing it within the microscope and they did this with the help of a unique vacuum-sealed holder.
“Our colleagues at Dow taught us how to handle air-sensitive materials, and that was a key element of this whole thing,” stated Kisielowski, “We are experts in controlling the electron beam, which is equally important. It was a give-and-take collaboration.”
Historically, an atomic level understanding of magnesium chloride has been difficult to achieve.
David Yancey, Project Collaborator, Dow
Yancey added that the close relationship between Dow and Berkeley Lab enabled them to apply the Foundry’s microscopy know-how to overcome this complicated problem.
By collaborating together, the research team at Dow and Berkeley Lab can deal with important scientific queries that are at the root of the complex industrial issues.
The institutional partnership is opening new avenues for future research. Addressing these big, fundamental questions will lead to far-reaching benefits across science, industry, and the nation’s economy.
Horst Simon, Deputy Director for Research, Lawrence Berkeley National Laboratory
Now that the catalysts for plastics production can be imaged at atomic resolution, the researchers will move toward exploring the associations between these structures and the characteristics of plastics, thus presenting new opportunities to develop more sustainable and specialized plastics.
We already know that we have to change how we deal with plastics in the world. If you want to make changes, you need to know how the process works. Hopefully, our new technique will help us in having a better understanding of how plastics form, and how we can make more sustainable materials.
Petra Specht, Study Second Author and Research Scientist, Department of Materials Science and Engineering, University of California, Berkeley
The Molecular Foundry is a DOE Office of Science User Facility. The study was supported by the DOE Office of Science, and by a DOE Cooperative Research and Development Agreement between Lawrence Berkeley National Laboratory and Dow.