FAU study shows that the extent of cross-linking between the polymer molecules is one of the key factors here.
Soft materials like rubber or silicone tear easily under tensile stress. In a project funded by the European Research Council (ERC), researchers from Friedrich-Alexander-Universität Erlangen-Nürnberg are looking for ways to make such materials more stable. In a current study, they have shown that it depends, at least partly, on how stable the crosslinked bonds are between the polymer molecules. If the crosslinks are too loose, this is just as detrimental to stability as if they are too strong. The study also used complex computer simulations. The findings may contribute towards developing high-tech plasters for securely closing wounds without stitches. Stable soft materials are also of interest for robotics or for creating stretchable electronics in items of clothing, known as wearables. The results were published in the journal npj Computational Materials.
If we keep pulling on an elastic band, sooner or later it will tear. In slightly thicker bands, for example those used to seal preserving jars, we observe that the tear generally runs vertically to the direction of the pulling force. In addition, it forms so rapidly that it often takes us by surprise: For a long time, the rubber remains completely intact in spite of the pulling force, until it suddenly tears without warning. “We call this non-linear behavior,” explains Dr. Miguel Angel Moreno-Mateos from the Institute of Applied Mechanics at FAU. “It makes the calculation of the fracture initiation and the spread of tears much more complicated than is the case for most solid materials.”
That is also the reason why fracture mechanics (which includes tears) of soft materials have not been researched sufficiently to date. The working group led by FAU NMP member Prof. Dr. Paul Steinmann now aims to change that. In 2022, Steinmann received an ERC Advanced Grant from the European Research Council for this purpose. Elastic yet stable materials are much sought after, for example for constructing robotic hands that can handle fragile objects, or for plasters that hold the edges of a wound firmly together even if the injured person stretches their muscles.
Virtual experiments facilitate the development of new materials
“We use highly complex physical models that allow us to simulate the behavior of soft materials on the computer,” Moreno-Mateos explains. As the equations can only be solved approximately, and not exactly, the simulations are based on special mathematical methods. Part of our research at the chair involves improving these procedures to provide quicker and more accurate simulations. “Our aim is to conduct virtual experiments on the computer that would be extremely tricky to do in real life,” explains the postdoctoral researcher. “This allows us to investigate which approaches are most promising for improving the stability of soft materials.”
In the study that has now been published, Moreno-Mateos and Steinmann have investigated how the tear strength changes in response to variations in the crosslinking between the polymer molecules. It became apparent that there is an optimal degree of crosslinking for obtaining maximum stability. The reason is that crosslinking changes the way in which the tear grows: At an ideal degree of crosslinking, the material first rips at the side, before turning 90 degrees and stretching over the direction of the pulling force. The material does not rip apart entirely. The researchers were able to confirm this result with their experiments. “It is like baking a cake,” the scientist explains: “Depending which ingredients you use in which ratio, you get a completely different result.”
Magnetic nanoparticles also increase stability
The working group is also experimenting with other procedures, partly also in international collaboration projects. They were able to demonstrate, for instance, that adding magnetic nanoparticles considerably increased the tear-resistance of elastomers. Electric fields also influence the initiation and spread of tears. “Our simulations have helped us gain a good understanding of how such effects are caused,” says Moreno-Mateos. “It is possible that in the medium term, our findings will contribute to the development of new materials with improved properties.”
Further information:
Dr. Miguel Angel Moreno-Mateos
Institute of Applied Mechanics
Phone: +49 9131 85-28508
miguel.moreno@fau.de
FAU study shows that the extent of cross-linking between the polymer molecules is one of the key factors here.
Soft materials like rubber or silicone tear easily under tensile stress. In a project funded by the European Research Council (ERC), researchers from Friedrich-Alexander-Universität Erlangen-Nürnberg are looking for ways to make such materials more stable. In a current study, they have shown that it depends, at least partly, on how stable the crosslinked bonds are between the polymer molecules. If the crosslinks are too loose, this is just as detrimental to stability as if they are too strong. The study also used complex computer simulations. The findings may contribute towards developing high-tech plasters for securely closing wounds without stitches. Stable soft materials are also of interest for robotics or for creating stretchable electronics in items of clothing, known as wearables. The results were published in the journal npj Computational Materials.
If we keep pulling on an elastic band, sooner or later it will tear. In slightly thicker bands, for example those used to seal preserving jars, we observe that the tear generally runs vertically to the direction of the pulling force. In addition, it forms so rapidly that it often takes us by surprise: For a long time, the rubber remains completely intact in spite of the pulling force, until it suddenly tears without warning. “We call this non-linear behavior,” explains Dr. Miguel Angel Moreno-Mateos from the Institute of Applied Mechanics at FAU. “It makes the calculation of the fracture initiation and the spread of tears much more complicated than is the case for most solid materials.”
That is also the reason why fracture mechanics (which includes tears) of soft materials have not been researched sufficiently to date. The working group led by FAU NMP member Prof. Dr. Paul Steinmann now aims to change that. In 2022, Steinmann received an ERC Advanced Grant from the European Research Council for this purpose. Elastic yet stable materials are much sought after, for example for constructing robotic hands that can handle fragile objects, or for plasters that hold the edges of a wound firmly together even if the injured person stretches their muscles.
Virtual experiments facilitate the development of new materials
“We use highly complex physical models that allow us to simulate the behavior of soft materials on the computer,” Moreno-Mateos explains. As the equations can only be solved approximately, and not exactly, the simulations are based on special mathematical methods. Part of our research at the chair involves improving these procedures to provide quicker and more accurate simulations. “Our aim is to conduct virtual experiments on the computer that would be extremely tricky to do in real life,” explains the postdoctoral researcher. “This allows us to investigate which approaches are most promising for improving the stability of soft materials.”
In the study that has now been published, Moreno-Mateos and Steinmann have investigated how the tear strength changes in response to variations in the crosslinking between the polymer molecules. It became apparent that there is an optimal degree of crosslinking for obtaining maximum stability. The reason is that crosslinking changes the way in which the tear grows: At an ideal degree of crosslinking, the material first rips at the side, before turning 90 degrees and stretching over the direction of the pulling force. The material does not rip apart entirely. The researchers were able to confirm this result with their experiments. “It is like baking a cake,” the scientist explains: “Depending which ingredients you use in which ratio, you get a completely different result.”
Magnetic nanoparticles also increase stability
The working group is also experimenting with other procedures, partly also in international collaboration projects. They were able to demonstrate, for instance, that adding magnetic nanoparticles considerably increased the tear-resistance of elastomers. Electric fields also influence the initiation and spread of tears. “Our simulations have helped us gain a good understanding of how such effects are caused,” says Moreno-Mateos. “It is possible that in the medium term, our findings will contribute to the development of new materials with improved properties.”
Further information:
Dr. Miguel Angel Moreno-Mateos
Institute of Applied Mechanics
Phone: +49 9131 85-28508
miguel.moreno@fau.de