A new approach to studying conjugated polymers enabled researchers to measure, for the first time, the individual molecules’ mechanical and kinetic properties during polymerization reaction.
Conjugated polymers are essentially clusters of molecules strung along a backbone that can conduct electrons and absorb light. This makes them a perfect fit for creating soft optoelectronics such as wearable electronic devices; however, as flexible as they are, these polymers are difficult to study in bulk because they aggregate and fall out from solution.
The approach, called magnetic tweezers, allows researchers to stretch and twist individual molecules of the conjugated polymer polyacetylene. Previous approaches relied upon chemical derivatization in which the structures are modified with functional groups of atoms; however, that approach can affect the polymer’s innate properties.
The process works by affixing one end of a polymer strand to a glass coverslip and the other end to a tiny magnetic particle. The researchers then use a magnetic field to manipulate the conjugated polymer, stretching or twisting it, and measuring the response of a single polymer chain that grows. The amounts are so small, they stay soluble in solution the way bulk amounts normally would not.
The team measured how long chains of conjugated polymers, which consist of hundreds of thousands of monomer units, grow in real time. They discovered the polymers add a new monomer per second, a much faster growth than their nonconjugated analogs. By pulling and stretching individual conjugated polymers, so-called force extension measurements, the researchers were able to assess their rigidity and better understand how they can bend in different directions while remaining conjugated and retaining electron conductivity.
They also discovered the polymers displayed diverse mechanical behaviors from one individual chain to the next — behaviors that had been predicted by theory but never observed experimentally. The findings highlight both the uniqueness of conjugated polymers for a range of applications as well as the strength of using a single-molecule manipulation and imaging technique on synthetic materials.