The polymer molecules are known as mechanophores. They are sensitive to the applied forces and can generate a quick change of their color when the material of interest is stressed. Their behavior has not been adequately studied but scientists suggest that there is great potential when it comes to material failure detection. Mechanophores practically enable a chemical reaction that triggers the color alteration when a load is applied hence, they provide a visual response of the stress that a material undergoes. Nevertheless, they are sensitive to the surrounding environmental factors such as humidity, temperature and light exposure.
The stress-state conditions of materials that are tested in the laboratory and (even more) in actual structures cannot always be recorded. Therefore, the utilization of mechanophores in the industry could revolutionize warning systems to better alert people when a potential structural failure is about to occur.
The research team from the University of Illinois at Urbana–Champaign has been working on the development of mechanophores for many years but has faced problems regarding their functionality. Precedent efforts resulted in materials that were too slow to react and could not return to their initial state after one load cycle. Hence, they did not present a clear linear behavior. However, new attempts have provided solutions and the derived molecules are able to generate quick and reversible color alterations when subjected to stresses. The findings of the team were recently published in Chem Journal.
When the mechanophore polymers are subjected to loads, the bonds between the chain are impacted and a color change reaction is triggered. Scientists utilized a new technique known as oxazine structure to achieve the reversible behavior of the material.
Jeffrey Moore, co-author of the study and Beckman Institute director, stated that the molecules can be used to provide new findings on the stress applied to all sorts of material including more than one industry (structural, health, biology industries, etc.). “In the area of biomechanics, for example, we see this research as a stepping stone toward better monitoring of how our bodies react to external forces from the cellular level and beyond,” Dr. Moore explained.
The developed mechanophores are planned to be used in in-situ applications.
A video with loading and unloading cycles of the new mechanophores can be found below. The color change is rapid and reversible in each cycle.