A research team led by Prof. Dr. Michael Sommer, holder of the Professorship of Polymer Chemistry at Chemnitz University of Technology, and PD Dr. Michael Walter, project leader at the Cluster of Excellence Living, Adaptive and Energy-autonomous Materials Systems (livMatS) at Albert Ludwig University Freiburg, has succeeded in constructing a new dye molecule from the field of so-called "mechanophores".
Thanks to this molecule, component stresses can be continuously indicated by colour changes depending on their strength. The concept of such dyes is not new, but previous mechanophores could usually only indicate the presence or absence of stresses in plastics. Current research now adds the dimension of the actual strength of the stress. This brings great advantages wherever it is important to have an overview of the stress and thus the integrity of the material at all times. The research team is now one step closer to developing this effective form of damage analysis and bringing it to practical application.
The results of the study have been published in Nature Communications.
Molecular "feather" shows the strength of the stress in terms of colour
As the researchers report in their publication, by combining a molecularly designed dye with a suitable and, above all, non-brittle plastic, macroscopic forces can now be transferred to the molecular scale. These acting forces can be, for example, external pressure or tension.
The dye molecule thus "feels" the force acting within the plastic and continues to indicate changes in force by changes in coloration. If the force on the plastic decreases, the dye molecule returns to its original state. This is why this dye is called a "molecular spring" - it stretches and then "springs" back to its original state.
Compared to existing molecular switches, which can indicate forces in plastics by changing color, the advantages here clearly lie in the stepless mapping of forces of different sizes as well as the spring-like behavior of the molecule, which can thus be used again and again.
Better mechanical properties - better understanding and applying damping
"This is a big step towards directly visualizing external stresses and residual stresses of plastics with simple analytics, which can be of great benefit for the further development of materials with improved mechanical properties or in the field of 3D printing," summarizes Prof. Dr. Michael Sommer.
But it could also make it easier to research the damping properties of special materials and also natural systems: For example, there are large and heavy fruits that fall from trees from great heights, but survive the fall undamaged. Nature serves as a model here and molecular springs could help to better understand and imitate such systems.
Future efforts will therefore focus on adapting molecular force springs for use in different plastics. This will require cooperation with other research groups and the use of computer-aided methods.