Organic Chemistry Seminar: Professor Takuzo Aida, University of Tokyo

"Stimuli-Responsive Smart Soft Materials"

About the Seminar:

Machine technology frequently puts magnetic or electrostatic repulsive forces to practical use, as in maglev trains, vehicle suspensions or non-contact bearings. In contrast, materials design overwhelmingly focuses on attractive interactions, such as in the many advanced polymer-based composites, where inorganic fillers interact with a polymer matrix to improve mechanical properties. However, articular cartilage strikingly illustrates how electrostatic repulsion can be harnessed to achieve unparalleled functional efficiency: it permits virtually frictionless mechanical motion within joints, even under high compression. Here we describe a composite hydrogel with anisotropic mechanical properties dominated by electrostatic repulsion between negatively charged unilamellar titanate nanosheets embedded within it. Crucial to the behaviour of this hydrogel is the serendipitous discovery of cofacial nanosheet alignment in aqueous colloidal dispersions subjected to a strong magnetic field, which maximizes electrostatic repulsion6 and thereby induces a quasi-crystalline structural ordering over macroscopic length scales and with uniformly large face-to-face nanosheet separation. We fix this transiently induced structural order by transforming the dispersion into a hydrogel using light-triggered in situ vinyl polymerization. The resultant hydrogel, containing charged inorganic structures that align cofacially in a magnetic flux, deforms easily under shear forces applied parallel to the embedded nanosheets yet resists compressive forces applied orthogonally. We anticipate that the concept of embedding anisotropic repulsive electrostatics within a composite material, inspired by articular cartilage, will open up new possibilities for developing soft materials with unusual functions. More recently, we reported a novel carbon nitride polymer, which shows anomalous mechanical responses to minute fluctuations in the ambient humidity.

References

1. Q. Wang, J. L. Mynar, M. Yoshida, E. Lee, M. Lee, K. Okuro, K. Kinbara, and T. Aida, Nature 2010, 463, 339–343.
2. M. Liu, Y. Ishida, Y. Ebina, T. Sasaki, and T. Aida, Nature Commun. 2013, 4, 2029
3. M. Liu, Y. Ishida, Y. Ebina, T. Sasaki, T. Hikima, M. Takata, and T. Aida, Nature 2015, 517, 68–72.
4. Y.-S. Kim, M. Liu, Y. Ishida, Y. Ebina, T. Sasaki, T. Hikima, M. Takata, and T. Aida, Nature Mat. 2015, 14, 1002–1007.
5. H. Arazoe, D. Miyajima, K. Akaike, F. Araoka, E. Sato, T. Hikima, M. Kawamoto, T. Aida, Nature Mat. 2016, in press.

About the Speaker:

Dr. Takuzo Aida was born in 1956. He received his Ph.D. in Polymer Chemistry from the University of Tokyo in 1984, and then began his academic career as an assistant professor at the same university on precision polymer synthesis. In 1996, he was promoted to full professor of the Department of Chemistry and Biotechnology, School of Engineering, the University of Tokyo. His research interests include optoelectronic soft materials, bioinspired macromolecules and materials including "Aqua Material", and molecular and biomolecular machines. He was appointed as a researcher for JST PRESTO Project for Fields and Reactions in 1996, and served as the director for JST ERATO AIDA Nanospace Project in 2000–2005 and then for JST ERATO-SORST Electronic Nanospace Project in 2005–2010. He is now the deputy director for Riken Center for Emergent Matter Science. He has received many awards including, as recent examples, American Chemical Society Award in Polymer Chemistry, Chemical Society of Japan Award in 2009, Purple Ribbon in 2010, and Fujiwara Prize and Alexander von Humboldt Research Award in 2011.