Scientists from the RIKEN Center for Advanced Photonics (RAP) in Japan have, for the first time, successfully used a terahertz laser to induce permanent changes in the conformation of a polymer, giving it an increased pattern of crystallization. Conformational changes are very important in macromolecular science because they can change the characteristics of a material and, in the case of proteins, can make it either possible or impossible for them to perform certain biological functions. This work, which was done in collaboration with researchers at Osaka University in Japan, is reported in a paper in Scientific Reports.

“Terahertz lasers offer promise as a way to modify materials, because they resonate at a frequency close to the oscillations of the hydrogen bonds that bind polymers into certain conformations, but are much lower in energy than the covalent bonds that make up the molecular structure of the polymers,” says Hiromichi Hoshina of RAP. “As a result, they could offer a ‘soft’ way to change the conformation without inducing chemical changes.”

One of the difficulties, however, of using terahertz wave irradiation to induce changes is that polymers tend to revert very quickly to a state of thermal equilibrium. To overcome this challenge, the group decided to perform experiments on a polymer undergoing solvent casting crystallization—a process that fixes its conformation. This allowed them to fix any changes, which could then be detected.

“We are excited by this work as this could give us a new tool for controlling the structure of ‘fragile’ molecules and allowing us to discover new functional materials.”Hiromichi Hoshina, RIKEN Center for Advanced Photonics

Their experiment was successful. When the group used a terahertz free electron laser to irradiate a polymer – a poly(3-hydroxybutylate)/chloroform solution – with terahertz radiation at a peak power of 40 megawatt/cm2, they found that the crystallization of the material increased by 20%.

“We were happy with these results, but we were also surprised by what we saw,” says Hoshina. The researchers were intrigued by the fact that the peak power used in this study was much lower than that used with near-infrared and visible lasers in previous attempts at inducing conformational changes in polymers. They considered whether the crystallization might have been caused by changes in temperature, but measured it and found that the difference between regions was less than 1°C, much too small to have an effect. They also considered whether the terahertz radiation might have caused increased vibrations between the molecules in the polymer, but did not find any significant correlations with the wavelength – something that should have happened if the effect was due to differences in resonance.

“We have, for the first time, shown that terahertz waves can effectively induce a rearrangement of the molecules in polymer macromolecules,” Hoshina explains. “The exact mechanism through which this happens remains a mystery, though we speculate that it might be related to the generation of shockwaves in the material, and we plan future work to find out exactly what is special about these terahertz waves, which have often been called the ‘unexplored frontier of the electromagnetic spectrum’.

“We are excited by this work as this could give us a new tool for controlling the structure of ‘fragile’ molecules and allowing us to discover new functional materials.”

This story is adapted from material from RIKEN, with editorial changes made by Materials Today. The views expressed in this article do not necessarily represent those of Elsevier. Link to original source.