For the first time, researchers from the RIKEN Center for Advanced Photonics (RAP), have successfully induced permanent alterations in the polymer conformation using a terahertz laser, thereby providing it with an increased crystallization pattern.
Low-magnification reflection images obtained by polarized microscope with cross-Nicol setup. (Credit: RIKEN Center for Advanced Photonics)
Conformational changes can alter the properties of a material. For instance, in proteins, such changes can make it feasible or infeasible for them to carry out a specific biological function; hence, conformational changes play a significant role in macromolecular science. This research was carried out in association with Osaka University and was reported 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. As a result, they could offer a ‘soft’ way to change the conformation without inducing chemical changes.
Hiromichi Hoshina from RAP elaborates
The materials have a tendency to quickly return to the state of thermal equilibrium states. This is one of the drawbacks of utilizing terahertz wave irradiation to stimulate changes in the materials. In order to resolve this limitation, the researchers conducted experiments on a polymer that was undergoing solvent casting crystallization, which is a process by which the conformation is fixed. This enabled the researchers to efficiently “fix” the results of the research and identify any alterations.
The experimental analysis turned out to be successful, because the material’s crystallization increased as much as 20%. To achieve this, the researchers used a terahertz free-electron laser FEL created by Osaka University’s Institute of Scientific and Industrial Research to irradiate a polymer i.e. poly(3-hydroxybutylate)/chloroform solution with THz radiation having a peak power of 40 MW/cm
We were happy with these results, but we were also surprised by what we saw.
However, the team were surprised by the fact that the peak power applied in this research was much lesser than the earlier reports using visible lasers and NIR. The researchers believed that changes in temperature might have caused crystallization; however, they went ahead and measured it and discovered that the variation between regions was less than 1°C, which is very small a variation to cause the difference. The researchers also believed that the THz waves might have led to increase in vibrations among the molecules but could not identify any considerable connections with the wavelength, which would have occurred if the effect was the result of the resonance difference.
We have, for the first time, shown that terahertz waves can effectively induce a rearrangement of the molecules in polymer macromolecules. 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,” continues Hoshina, “as this could give us a new tool for controlling the structure of ‘fragile’ molecules and allowing us to discover new functional materials.”