Ideal nanocrystal produced from bulk plastics

Polymer chain incorporation during formation of ideal PE-nanocrystals by catalytic insertion polymerization with a water-soluble Ni(II) catalyst. The amorphous layers covering both platelets act as the wheels of a pulley just changing the direction of the chains. A moderate raise of the temperature induces sufficient mobility that allows the chains to move within the crystal.

Polymer chain incorporation during formation of ideal PE-nanocrystals by catalytic insertion polymerization with a water-soluble Ni(II) catalyst. The amorphous layers covering both platelets act as the wheels of a pulley just changing the direction of the chains. A moderate raise of the temperature induces sufficient mobility that allows the chains to move within the crystal.

Polyethylene is an inexpensive commodity plastic found in many household objects. Now, a consortium of researchers from Constance, Bayreuth, and Berlin has successfully used this plastic to synthesize the ideal polymer nanocrystal. The prerequisite was a new type of catalyst produced by Constance University researchers as well as a combination of unique analytic tools like those found at the Helmholtz Zentrum Berlin (HZB). The crystalline nanostructure, which gives the polymer its new properties, could prove of interest to production of new kinds of coatings. The scientists’ findings are being published in the Journal of the American Chemical Society’s current issue (DOI: 10.1021/ja4052334).

Bringing materials with a disordered (amorphous) molecular structure into a crystalline form is a common endeavor pursued by chemists and material scientists alike. Often, it is only the crystalline structure which gives a material its desired properties. Therefore, basic science researchers have been interested in trying to identify physical principles that underlie the transition from a structure’s amorphous to its crystalline phase.

The most effective analytic tool that is needed for this is really a combination of various methods that are nowhere as concentrated as they are in Berlin. For the last three years, the HZB and Humboldt University Berlin have been running their Joint Lab for Structural Research. For Humboldt University, the lab was a key factor in their excellence initiative concept.

High polymer compounds like polyethylene, which exist as long molecular chains, are typically partly crystalline, meaning they consist of lamellar-like polyethylene crystals that are coated by a layer of amorphous polyethylene. These amorphous phases are characterized by a series of imperfections like knots. However, within an “ideal” nanocrystal, the amorphous regions act like deflection pulleys that change the direction of chains within the crystal by 180 degrees (see image).

Synthesis of such an ideal crystal has now been accomplished with the help of a new water-soluble catalyst, which allows for polymerization of ethylene in the aqueous phase. In the process, newly developing parts of the molecular chain are immediately incorporated into the growing crystal so that imperfections like entanglements are not allowed to form within the amorphous regions. The researchers gleaned these insights using X-ray diffraction methods and cryogenic transmission electron microscopy (TEM).

The nanocrystal suspension was produced by Prof. Stefan Mecking’s group at Constance University. For the cryo-TEM, HZB scientist Prof. Matthias Ballauff and his team produced a thin film of an aqueous polyethylene nanocrystal suspension and shock-froze it using cryogenically liquefied ethane. This resulted in formation of a glass-like solidified water modification, and the polyethylene nanocrystals enclosed within it can be analyzed using an electron microscope. The suspensions were also subjected to small-angle X-ray scattering (SAXS).

At a resolution of approximately one nanometer, the cryo TEM is the perfect tool for studying the tiniest structures within microemulsions and colloidal solutions. Along with X-ray diffraction experiments, this method has helped document the presence of perfect polymer nanocrystals. Says Matthias Ballauff: “This work shows that by combining microscopy and scattering, even complex systems can be analyzed with a degree of precision that is impossible using either method alone.”

Original article in Journal of the American Chemical Society:

IH

  • Copy link

You might also be interested in

  • Porous Radical Organic framework improves lithium-sulphur batteries
    Science Highlight
    15.09.2025
    Porous Radical Organic framework improves lithium-sulphur batteries
    A team led by Prof. Yan Lu, HZB, and Prof. Arne Thomas, Technical University of Berlin, has developed a material that enhances the capacity and stability of lithium-sulphur batteries. The material is based on polymers that form a framework with open pores (known as radical-cationic covalent organic frameworks or COFs). Catalytically accelerated reactions take place in these pores, firmly trapping polysulphides, which would shorten the battery life. Some of the experimental analyses were conducted at the BAMline at BESSY II.
  • Metallic nanocatalysts: what really happens during catalysis
    Science Highlight
    10.09.2025
    Metallic nanocatalysts: what really happens during catalysis
    Using a combination of spectromicroscopy at BESSY II and microscopic analyses at DESY's NanoLab, a team has gained new insights into the chemical behaviour of nanocatalysts during catalysis. The nanoparticles consisted of a platinum core with a rhodium shell. This configuration allows a better understanding of structural changes in, for example, rhodium-platinum catalysts for emission control. The results show that under typical catalytic conditions, some of the rhodium in the shell can diffuse into the interior of the nanoparticles. However, most of it remains on the surface and oxidises. This process is strongly dependent on the surface orientation of the nanoparticle facets.
  • Key technology for a future without fossil fuels
    Interview
    21.08.2025
    Key technology for a future without fossil fuels
    In June and July 2025, catalyst researcher Nico Fischer spent some time at HZB. It was his sabbatical, he was relieved of his duties as Director of the Catalysis Institute in Cape Town for several months and was able to focus on research only. His institute is collaborating with HZB on two projects that aim to develop environmentally friendly alternatives using innovative catalyst technologies. The questions were asked by Antonia Rötger, HZB.