The Ouchi lab develops novel responsive materials systems whose response propagates across, or couples with, multi-length scale phenomena. It centers on the interfaces of materials science, polymer/mechanochemistry, and soft matter mechanics. Material systems in nature represent the ultimate examples of smart materials and possess versatile responsive/autonomous functions through their sophisticated yet complicated structures. They (i) take advantage of their structural inhomogeneity, (ii) transduce their local responses as chemical/electrical signals, and (iii) organically adapt to their environments through cooperative interactions in which multi-scale and multidisciplinary phenomena are involved. However, because of these complexities in their systems, there are still large gaps between artificial material systems and natural objects. Our group has interdisciplinary experiences across Polymer Science, Mechanical Engineering, and Chemistry. This combination of experiences enables us to explore the questions of atomic-to-macroscopic coupling in material systems at various length scales that are central to our research program. With technologies in these fields, we are interested in reverse-engineering these essences from natural objects and will provide advanced materials platforms that address technical challenges currently faced in the areas of healthcare, environmental sustainability, and manufacturing.

Mechanochemistry, where chemical reactions are induced in response to force, allows us to turn destructive chemical bond breakages into constructive chemical responses. Examples include stress-induced color changes, stress-strengthening, force-triggered degradation, and the release of small molecules.

In the Craig group, we designed and synthesized a new thermally-stable mechanophore that combines two functions: it generates HCl and increases its molecular toughness in response to mechanical stimuli. By incorporating this mechanophore into a double-network hydrogel, we further realized a mechanically robust hydrogel platform that shows substantial acidification from pH ~7 to ~5 under mechanical loading (Figure. 1a). We also used mechanophores (e.g., spiropyran) as molecular force probes to investigated how the deformation and tension experienced by a strand within a strained network is influenced by strand length. We synthesized a polymer network incorporating molecular force probes and revealed a molecular force transduction behavior inside the network under macroscopic deformation (Figure. 1b).

Key words: Mechanochemistry, Smart materials, Tough materials, Monomer/Polymer synthesis

Related publications (* equal contribution, † undergradaute mentee):

• Tetsu Ouchi*, Wencong Wang*, Brooke E. Silverstein†, Jeremiah A. Johnson, Stephen L. Craig, “Effect of strand molecular length on mechanochemical transduction in elastomers probed with monodisperse force sensors”, Polymer Chemistry, 14, 1646-1655 (2023). Impact Factor: 4.6 https://doi.org/10.1039/D3PY00065F 

• Tetsu Ouchi*, Brandon Bowser*, Tatiana B. Kouznetsova, Xujun Zheng, Stephen L. Craig, “Strain-triggered acidification in a double-network hydrogel enabled by multi-functional transduction of molecular mechanochemistry”, Materials Horizons, 10, 585-593 (2023). Impact Factor: 13.3 https://doi.org/10.1039/D2MH01105K  

• Zi Wang, Xu Jun Zheng, Tetsu Ouchi, Tatiana Kouznetsova, Haley Beech, Sarah Av-Ron, Brandon Bowser, Shu Wang, Jeremiah Johnson, Julia Kalow, Bradley Olsen, Jian Ping Gong, Michael Rubinstein, Stephen Craig, “Toughening hydrogels through force-triggered chemical reactions that lengthen polymer strands”, Science, 374, 6564, p. 193-196 (2021). Impact Factor: 56.9 DOI: 10.1126/science.abg2689 

Natural objects use mechanical instabilities, such as wrinkling and creasing, to elegantly realize their unique properties. Therefore, researchers have been trying to reverse-engineer mechanical instabilities. However, it has been difficult to control these instabilities due to the lack of understanding on (i) their formation mechanisms and (ii) the interplays among these instabilities, where different instability modes compete on a single surface.

In the Hayward group, we built a high-speed image capture system, which enabled controlled strain rate and humidity, and experimentally elucidated the mechanism of crease formation (Figure 2a). Also, through micropatterning an elastomer surface by photolithography, we found a rich set of surface morphologies composed of multiple instability modes (e.g., wrinkling, creasing, folding) (Figure 2b left). We further applied these findings to flexible electronics devices and demonstrated mechanically-gated electrical switches and mechanical logic gates (Figure 2b right). 

Key words: Soft matter mechanics, Mechanical instabilities, Flexible electronics 

Related publications (* equal contribution):

• Tetsu Ouchi, Ryan C. Hayward, “Harnessing multiple surface deformation modes for switchable conductivity surfaces”, ACS Applied Materials & Interfaces, 12, 8, p. 10031-10038 (2020). Impact Factor: 9.5 https://doi.org/10.1021/acsami.9b22662 

• Qihan Liu*, Tetsu Ouchi*, Lihua Jin, Ryan C. Hayward, Zhigang Suo, “Elastocapillary Crease”, Physical Review Letters, 122, 098003 (2019). Impact Factor: 8.6 https://doi.org/10.1103/PhysRevLett.122.098003

• Tetsu Ouchi*, Jiawei, Yang*, Zhigang Suo, Ryan C. Hayward, “Effects of stiff film pattern geometry on surface buckling instabilities of elastic bilayers”, ACS Applied Materials & Interfaces, 10, p. 23406-23413 (2018). Impact Factor: 9.5 https://doi.org/10.1021/acsami.8b04916  

Semicrystalline polymer, such as polyethylene (PE) and polypropylene (PP), is a commercially important class of polymers. As it is often used under mechanical loading, its mechanical properties and associated microstructures (e.g., crystals) are key to investigate for its applications.

In the Hotta group, we studied the crystalline structures of syndiotactic polystyrene (sPS) and found a new β to α form crystalline transition under mechanical deformation (Figure 3a). Also, we investigated the structure-property relationships of stereoregular polypropylenes (iPP and sPP) and their gels (Figure 3b). Through rheological analyses, we revealed similarities in their mechanical responses between molten PPs and organo PP gels. 

Key words: Rheology, Polymer microstructures, Semicrystalline polymers, Stereoregular polymers

Related publications:

• Tetsu Ouchi, Misuzu Yamazaki, Tomoki Maeda, Atsushi Hotta, “Mechanical property of polypropylene gels associated with that of molten polypropylenes”, Gels, 7, 99 (2021). Impact Factor: 5.2 https://doi.org/10.3390/gels7030099  

• Tetsu Ouchi, Suguru Nagasaka, Atsushi Hotta, “β to α Form Transition Observed in the Crystalline Structures of Syndiotactic Polystyrene (sPS)”, Macromolecules, 44, p. 2112-2119 (2011). Impact Factor: 5.5 https://doi.org/10.1021/ma200166m