Ring-shaped polymer solidifies into glass, offering potential for sustainable materials

When a spider spins a web, the thread starts out as a liquid and quickly turns into a solid that is stronger than iron. They were able to create these amazing materials at room temperature using biodegradable and environmentally friendly polymers. Materials scientists at Carnegie Mellon University are studying these processes to better understand how biological systems manipulate polymers and how the techniques can be borrowed to improve the processing of industrial plastics. I am researching.

One of the unique properties of polymers is that their molecules can have different shapes or “structures” and these shapes can have a significant impact on material properties and recyclability. Polymer chains can form molecular strings, mesh-like networks, and even closed rings.

New discoveries about how ring-shaped polymers behave have the potential to enable new ways for polymer scientists to design more sustainable materials. A research team from Carnegie Mellon University, Sandia National Laboratories, and the University of Illinois at Urbana-Champaign (UIUC) has conducted the largest-ever simulations of this type of polymer, confirming theoretical predictions and showing that ring polymers naturally He discovered that it solidifies into glass. When the chain is long enough.

The study, published in the Proceedings of the National Academy of Sciences, shows how changing the shape of a polymer from an open string to a closed ring completely changes the way molecules pack and diffuse within the material. Masu. The researchers found that as the cyclic polymer became longer, the separate chains became more and more tightly packed until the chains became immobile and the material solidified. The simple act of changing the molecular shape from an open string to a closed ring also changed the phase of the plastic from a liquid to a solid.

“Typically, solidifying molten plastic requires lowering the temperature of the sample, but we found that simply changing the shape of the molecules into rings slows them down and vitrifies them into glass.” said Thomas O’Connor, assistant professor of science. I studied engineering at Carnegie Mellon University.

O’Connor and materials science and engineering doctoral student Songyue Liu spent more than a year running large-scale molecular dynamics simulations on a Department of Energy supercomputer to test theoretical predictions developed by their UIUC colleagues. did. The simulation built on previous work by the team, which experimentally synthesized a recyclable polymer material consisting of a pure cyclic polymer that unexpectedly vitrified in the lab. These new theoretical results will explain this surprising behavior and guide the design of recyclable cyclic polymers.

This research also has implications for the behavior of biopolymer systems such as chromosomes, which bundle and store folded proteins and DNA. These biological systems adopt a loop-like structure similar to the ring polymers investigated by the research team.

“Understanding how looped polymer structures pack and fold into each other is insightful for materials science, but living systems need to integrate these structures to enable biological functions. It’s also important to understand why you use it,” says O’Connor. “We have the potential to draw parallels between these fields and make new discoveries.”