When molecules undergo a force, bonds often weaken or break apart. But scientists have discovered a scenario in which the application of force could actually help make materials stronger. Certain strings of atoms, used as the backbone of a molecule on which a reaction takes place, can accelerate that reaction by up to 1000 times when a force is applied. This has led to these groups being called ‘molecular levers’ and it is hoped they will have exciting consequences for the development of new materials.
Chemist Steve Craig and his team from Duke University in the USA have done experiments comparing a polynorbornene and a polybutadiene scaffold. They measured how quickly a ring embedded within the molecule was opened when it was pulled apart using the equivalent of microscopic tweezers. They found that the reaction happened 1000 times faster with a polynorborene backbone than with a polybutadiene backbone, suggesting the polynorborene acts as a kind of ‘molecular lever’ to accelerate these mechanically forced reactions.
This particular discovery came as part of the group’s long-term research into designing new, stress-responsive materials. We know from the wear-and-tear encountered in everyday objects such as bike breaks and the soles of shoes that many materials break down after being repeatedly subjected to a force. However, Craig hopes to use the force on a material to actually make it stronger by developing reactions that are very slow normally but can be accelerated by force. This means that reactions that could strengthen or extend the lifetime of the material could be triggered at the specific place where the material undergoes the most stress. The group’s most recent discovery about the control they can exert over the rates of such reactions will provide a valuable starting point for further investigations into making more efficient and responsive materials, which will have many important applications from military defence technology to biomedical implants.
