Jul 27, 2023 |
How molecular entanglements determine the structure of polymers
(Nanowerk News) The structure of semi-crystalline polymers largely depends on how strongly their molecular chains are entangled. This has been shown in a new study by researchers from Martin Luther University Halle-Wittenberg (MLU) which was published in the scientific journal Proceedings of the National Academy of Sciences" ("How entanglements determine the morphology of semicrystalline polymers").
|
Following numerous experiments, the researchers developed a new model to predict the microscopic structure of the materials as well as their properties. Polymers are long-chain molecules. Semi-crystalline polymers are a mixture of solid and liquid elements. They are often used in plastics and packaging materials.
|
When materials cool down, they usually form a crystalline structure at the molecular level, in other words, all the particles are in a tightly ordered pattern. "A similar process occurs when semi-crystalline polymers form, except that not all regions crystallise," explains physicist Professor Thomas Thurn-Albrecht from MLU. Instead, there are so-called amorphous regions that have a disordered structure after cooling. Here entanglements that are intertwined with one another are found.
|
In semi-crystalline polymers, ordered and disordered layers alternate over and over on a nano-level. This special structure also gives them their unique properties: they are both flexible and elastic as well as being relatively robust. This makes them particularly suitable as packaging and structural materials.
|
The properties of semi-crystalline polymers largely depend on two factors: the thicknesses of the above mentioned layers and how strongly the chains in the amorphous regions are entangled. According to Thurn-Albrecht, the factors that influence crystal thickness are already well-known, yet knowledge about amorphous layers is still rather limited. His team investigated the process of crystal formation specifically for these layers in collaboration with a group led by professor Kay Saalwächter from MLU.
|
Based on their measurements on a model polymer, the physicists discovered that the thickness of the amorphous layers is determined to a large extent by their entanglements. The researchers also developed a simple model to describe this relationship.
|
"We assume that our model can be applied to many different polymers. That includes materials that, at the moment, are not used very widely," says Thurn-Albrecht. The new findings could help to improve existing materials or to replace them - either completely or in part - with more sustainable alternatives.
|