A phenomenon of "photoexpansion" in hard plastic films with a high glass transition temperature in the dry state was established, which was essentially different from very soft actuators, such as elastomers or gels. The photoexpanding hard actuators were expected to apply in the wide fields because they do not contain vaporable matters such as solvents and were much more thermoresistant than conventional ones.
Ishikawa, April 22, 2021 - Polymers that exhibit their functions by light have been studied for a few decades because they enable device miniaturization, energy saving, and precise signal control. Polymers based on azobenzene, diarylethene, etc. are the pioneers, and many examples of light-driven motors and artificial muscles have been reported. On the other hand, cinnamic acid, which is a constituent of lignin in natural wood, also exhibit the function by ultraviolet (UV) rays, so that it has been applied to polymers. The deformation mechanism of these cinnamate-based polymers has not been clarified because the two reactions of double bond cis-trans isomerization and [2+2] cycloaddition occur almost simultaneously. Since the mechanism has not been clarified, its use as a photodeformable material has not received as much attention as the above-mentioned azobenzene and diarylethene.
To tackle these issues, a team of researchers from Japan Advanced Institute of Science and Technology (JAIST) are investigating photobending mechanism of bio-based polycinnamete films. Their latest study, published in ACS Applied Materials & Interfaces, was led by Professor Tatsuo Kaneko and Assistant Professor Kenji Takada also involved Professor Hideyuki Murata, Associate Professor Kosuke Okeyoshi, and Research Assistant Professor Amit Kumar.
In this study, polyesters were synthesized based on coumarates in which hydroxyl groups were substituted in the aromatics of cinnamate. Among them, those showing photodeformability were poly(3-hydroxycinnamic acid) (P3HCA) and poly(3,4-dihydroxycinnamic acid) (PdHCA). Although both films had a cinnamate unit, P3HCA showed convex deformation with respect to an UV source, and PdHCA showed concave deformation, respectively. These differences were analyzed by various spectral analyzes. First, when the fluorescence lifetime was measured, it was found that there are two excited states in P3HCA. Next, by time-resolved infrared (IR) spectroscopic measurement, the absorption of the double bond of the cinnamate unit was traced from the change in the IR spectrum during UV irradiation. In case of P3HCA, it was confirmed that the absorption of cis-formed -CH=CH- bond was increased by increasing the UV irradiation time. On the other hand, in PdHCA, no change in the absorption of cis-formed -CH=CH- was confirmed. To prove these photoexpansions, an experiment was conducted in which a P3HCA film was covered with a photomask and UV rays were irradiated from above. When the free-standing film was irradiated with UV through a photomask, the non-irradiated surface also showed a deformation. Therefore, when an irradiation experiment was conducted with the P3HCA film coated on the glass substrate, there was no deformation of the surface, opposite side, not irradiated with UV, and no deformation of the part covered with the photomask was observed. From the above results, it was found that P3HCA exhibits convex deformation by "expanding" with respect to UV owing to cis isomerization.
There is no other example that is bio-based and can control the deformation with respect to UV light. In addition, by elucidating the deformation mechanism of polycinnamates through this research, precise control of photodeformability based on a dense polymer design can be expected. The fact that the photodeformability differs depending on the "shape" of the molecule, as Prof. Kaneko explains: "even though they are the same constituents, deformation behaviors were different. These results strongly support the correlation between the structure and physical properties of the cinnamate-based polymers, and this study become the good perspective of the bio-based and photoresponsive polymers." In addition, they consider, it can be expected to greatly contribute to the development of new materials based on the molecular design.
Further progress in bio-based polycinnamate as photodeformable materials will hopefully get us closer to more precisely controllable actuator and a sustainable society.
Title of original paper: "Photoexpansion of Biobased Polyesters: Mechanism Analysis by Time-Resolved Measurements of an Amorphous Polycinnamate Hard Film"
Journal: ACS Applied Materials & Interfaces (ACS Publications)
About Japan Advanced Institute of Science and Technology, Japan
Founded in 1990 in Ishikawa prefecture, the Japan Advanced Institute of Science and Technology (JAIST) was the first independent national graduate school in Japan. Now, after 30 years of steady progress, JAIST has become one of Japan's top-ranking universities. JAIST counts with multiple satellite campuses and strives to foster capable leaders with a state-of-the-art education system where diversity is key; about 40% of its alumni are international students. The university has a unique style of graduate education based on a carefully designed coursework-oriented curriculum to ensure that its students have a solid foundation on which to carry out cutting-edge research. JAIST also works closely both with local and overseas communities by promoting industry-academia collaborative research.
About Professor Tatsuo Kaneko and Assistant Professor Kenji Takada from Japan Advanced Institute of Science and Technology, Japan
Tatsuo Kaneko received a B.S. in Tokyo Tech in 1993, and a Ph.D. in Polymer Chemistry from the same university in 1998. One year before received Ph.D., he joined the faculty as an Assis Prof at Hokkaido Univ, and then moved to Kagoshima Univ and Osaka Univ. After that, he joined JAIST and promoted to Full Professor in 2016. He also joined UCLA as a Visiting Assoc Prof under the acceptance of Prof. Timothy Deming in 2012. Current research interests include soft matters, polyelectrolytes, and bioplastics, for which he has received awards from Chemical Society of Japan and from several foundations. International prizes such as "Best presentation" at the 251st ACS National Meeting, "Distinguished Award" at the 12th IUPAC NMS-XII, and "Gottfried Wagener prize" The 9th German Innovation Award have also been given.
Kenji Takada received his B.S in Hokkaido University in 2011, and a Ph.D. in Polymer Chemistry from the same university in 2015. He was subsequently appointed as a researcher and post doctor as JSPS research fellow for young scientists DC1 and PD. In 2021, he joined to JAIST as an Assistant Professor. His research interests are living anionic or radical polymerization of vinyl monomers. He is also studying about biomolecules-based plastics, high-performance polymers, and photo-functionalized materials.
This study was supported by the JST-ALCA Program (grant umber JPMJAL1010).
ACS Applied Materials & Interfaces