Chemistry graduate student Anna Overholts examines a piece of polymer stamped with a stress pattern indicated by blue dye (Photo – Lance Hayashida/Caltech)
Stress isn’t just the psychological pressure you feel in response to a looming deadline at work. It is also a description of the physical forces pushing, pulling, or twisting an object, structure, or material.
By Emily Velasco, Caltech
Examples of stress include gravity dragging downward on a bridge, wind blowing against the side of a building, or even a waistband drawn taut by a big meal.
With stress affecting literally everything made and used by people, often in damaging ways, it is important to identify when and where it is happening and the extent to which it is occurring. This is not always easy, though, because many materials show no obvious signs of being under stress.
Caltech’s Maxwell Robb, an assistant professor of chemistry, has been working to make stress easier to identify through the creation of polymers that change color when a force is applied to them. Now, in a paper published in Nature Chemistry, Robb shows how his team created a new type of polymers that can be made to change to almost any colors the user wants.
To create a plastic that changes color in response to stress, you need a type of molecule known as a mechanophore.
When mechanophores are incorporated into a plastic, they experience the force that is applied to the plastic and thus will change color, allowing the location of that stress to be visualized.
The team’s latest work is based on similar principles but with a twist. The mechanophore they have developed doesn’t change color directly with force but rather produces an intermediate compound that can be converted to myriad brightly colored dyes. called donor–acceptor Stenhouse adducts (DASAs).
Robb says the ability to leave chemically reactive imprints in three dimensions in polymer materials could also open the door to patterning other kinds of chemicals in three-dimensional space, such as proteins, which would have applications in tissue engineering.”
The paper describing the work is titled “Mechanically gated formation of donor– acceptor Stenhouse adducts enabling mechanochemical multicolour soft lithography.” Co-authors are chemistry graduate student Anna C. Overholts and undergraduate student Wendy Granados Razo.
> Read the full article at Caltech’s website.
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