(2fh) Advanced Material Systems That Harness Inhomogeneity and Multi-Scale Phenomena

Research Interests:

My future research program will develop novel responsive materials systems whose signals propagate across, or couple with, multi-length scale phenomena. Specifically, my research program will establish (i) geometry-coupled mechanically adaptive systems, (ii) tough elastomeric materials through topology-induced energy dissipation, and (iii) mechano-responsive material systems leveraging high-intensity focused ultrasound (HIFU). The central research questions span traditional fields of materials science, polymer (mechano)chemistry, and soft matter mechanics, but they are united by a set of common characteristics: (i) They take advantage of structural inhomogeneity; (ii) they transduce local responses as chemical/electrical signals; and, (iii) they involve materials that adapt to their environments through multi-scale cooperative phenomena (e.g., chemical reactions at the atomic scale and mechanical instabilities at the nm to cm scales).

Through my research journey, I am fortunate to have had access to interdisciplinary experiences across Polymer Science, Mechanical Engineering, and Chemistry. This rare combination of experiences has prepared me to explore the questions of atomic-to-macroscopic coupling in material systems at various length scales that are central to my research program. The material platforms developed in my lab, and the knowledge we create, will fuel new approaches to high performance health care devices, flexible electronics, environmentally sustainable rubbers and gels, and 3D composite fabrications.

Research Experience:

Postdoctoral Associate – Stephen L. Craig group, Department of Chemistry, Duke University

“Polymeric Material Systems Leveraging Mechanochemistry”

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, I 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, I realized a mechanically robust hydrogel platform that drops its pH from ~7 to ~5 in response to mechanical loading. I also used mechanophores (e.g., spiropyran) to probe how the deformation and tension experienced by a strand within a strained polymer network is influenced by strand length. I synthesized a polymer network incorporating molecular force probes and revealed a molecular force transduction behavior inside the network under macroscopic deformation.

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

Related awards and honors: “2023 Polymeric Materials: Science and Engineering (PMSE) Future Faculty Honoree” by American Chemical Society (2023), “3rd Place Poster Award” at the Triangle Soft Matter Workshop (2023)

Ph.D. – Ryan C. Hayward group, Department of Polymer Science and Engineering, University of Massachusetts Amherst

“Mechanical Instabilities on a Soft Elastic Substrate”

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

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

Related awards and honors: “3rd place for the 2017 Journal of Polymer Science poster prize” by the American Physical Society (2017), Editor’s suggestion in the journal of Physical Review Letters (2019)

M.S. and B.S. – Atsushi Hotta group, Department of Mechanical Engineering, Keio University, Japan

“Mechanical/Rheological Properties and Microstructures of Stereoregular Polymers”

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

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

Related awards and honors: “Excellence in Graduate Polymer Research” by the American Chemical Society (2011)

Teaching Interests:

Education is one of the most important motivations that inspired me to become a faculty member. To me, education is not only the act of passing down knowledge and skills from one generation to the next, but also supporting students and mentees in developing their curiosities, finding their passions, and growing as human beings. I had privilege to have experiences in teaching, mentoring, and outreach activities at Keio University in Japan, UMass Amherst, and Duke University. These experiences allowed me to interact with students from different scientific backgrounds (i.e., material science, mechanical engineering, chemistry), enabling me to have teaching approaches from interdisciplinary viewpoints. After becoming an assistant professor, I will strive to provide guidance, support, and opportunities with the mission to educate students and mentees to be independent researchers equipped with proper scientific knowledge, skills, and ethics.

Given my research and education background in mechanical engineering, polymer science, and chemistry, I am excited to teach a range of topics. For example, I am interested in teaching polymer physics, polymer engineering, polymer chemistry, material characterization, mechanics of materials, thermodynamics, and mechanochemistry.

Teaching and Mentoring Experience:

Duke University (Department of Chemistry)

Mentored 1 master student and 6 undergraduate students

Taught reaction mechanisms and synthesis procedures in the class of “Independent Study” for undergraduate students

University of Massachusetts Amherst (Department of Polymer Science and Engineering)

Mentored 1 undergraduate student for Independent Research Project

Keio University (Department of Mechanical Engineering)

Worked as TA in the class of “Practice in Mechanical Engineering Projects”

Mentored 2 graduate and 2 undergraduate students

Selected Publications (11 total, 7 first author, 278 citations):

* Equal contributors, ^† Undergraduate 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). 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). https://doi.org/10.1039/D2MH01105K

Tetsu Ouchi, Ryan C. Hayward, “Harnessing multiple surface deformation modes for switchable conductivity surfaces”, ACS Applied Materials & Interfaces, 12, 8, p. 10031-10038 (2020). 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). https://doi.org/10.1103/PhysRevLett.122.098003

Selected as Editors’ Suggestion

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). https://doi.org/10.1021/acsami.8b04916

Tetsu Ouchi, Misuzu Yamazaki, Tomoki Maeda, Atsushi Hotta, “Mechanical property of polypropylene gels associated with that of molten polypropylenes”, Gels, 7, 99 (2021). 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). https://doi.org/10.1021/ma200166m

Honors and Awards:

3rd Place Poster Award” at the Triangle Soft Matter Workshop, May 2023

2023 Polymeric Materials: Science and Engineering (PMSE) Future Faculty Honoree by the American Chemical Society at ACS Fall 2023 Meeting

The 2017 Journal of Polymer Science poster prize (3rd place in APS DPOLY poster competition) by the American Physical Society at APS March Meeting, March 2017

Exempted from returning finance loan from Japan Student Services Organization, about $26,400 (2,112,000 yen), for excellent achievements and high grades, May 2012

Excellence in Graduate Polymer Research by the American Chemical Society at 241st ACS National Meeting & Exposition, March 2011

Keio Graduate Scholarship, about $6,410/year (500,000 yen/year), by Keio University for 2 consecutive years (2010-2012)

Hatakeyama Prize for the 2nd highest grades in mechanical engineering at Keio University by The Japan Society of Mechanical Engineers, March 2010, 1 of 2 (out of 166 candidates)