(3iq) Polymer Physics Guided Design and Processing of Functional Polymers

Material design for future electronics will feature not only mechanical flexibility for display or energy harvesting devices but also stretchability, super-softness, and shape customization for more intimate and seamless integration with the human body. The overall research theme of my nascent independent career strives to study fundamental structure–processing–property relationships that improve the human–technology integration of next-generation bioelectronic devices and optics via novel materials design. My group will specialize in polymer physics, rheology, and 3D printing, aiming to reveal fundamental insights that guide the materials design and processing of functional polymers, such as the semiconducting conjugated polymer and the entanglement-free bottlebrush polymer. My approach involves (1) forming a synergistic hybrid of conjugated–bottlebrush polymers as super-soft and highly stretchable conductors, where charge transport pathways along the conjugated backbone remain unperturbed with a low modulus (1–100 kPa) that is controlled by the bottlebrush architecture, (2) driving the nematic ordering of mesogen-free bottlebrush polymer by designing an extremely congested sidechain, and (3) developing new ink formulations to 3D print conducting elastomers by leveraging the yield-stress fluid behavior. Three specific research objectives include:

1. Advanced Processing of Conjugated Polymer, Bottlebrush Polymer, and their Blends
2. Super-Soft Conducting Elastomers: Conjugated–Bottlebrush Hybrid Polymer Networks

• Mesogen-Free Liquid-Crystal Bottlebrush Polymers for Optical and Biomedical Applications

This proposed research program is multidisciplinary, covering polymer science, additive manufacturing, electronics, and biology.

SEE IMAGE

Figure 1. Overview of my proposed research. Image of Jellyfish depicts the super-soft modulus, which can be achieved by synthetic solvent-free bottlebrush elastomer. Images for the tensile test and 3D printed bowl-shaped object (scale bar = 1.0 mm) are from my previous works.

Since November 2018, I have been a postdoctoral scholar working with Professors Michael Chabinyc and Chris Bates at the University of California, Santa Barbara. I received dual B.S. degrees in chemical engineering and materials science & engineering from the University of Minnesota Twin Cities, where I was intrigued by the non-Newtonian behavior of polymers as an undergraduate researcher in Prof. Chris Macosko’s group. I then decided to attend graduate school at Pennsylvania State University, where I completed a Ph.D. in chemical engineering under the supervision of Professors Ralph Colby and Enrique Gomez. Researching across different groups not only enriched my learning experiences in different disciplines but also trained me to work effectively in a collaborative environment. Besides my expertise in rheology, polymer physics, and 3D printing, I have developed working knowledge of polymer synthesis (e.g. Grignard metathesis and ring-opening metathesis polymerization) and device fabrication (e.g. semiconductors and sensors) and established long-term collaborations with my doctoral and postdoctoral colleagues.

My postdoctoral work involves discovering and understanding the unique physical properties of bottlebrush polymers for innovative applications. In particular, I have recently developed a facile, room-temperature 3D printing technique to print super-soft and solvent-free elastomers by leveraging the unique self-assembly of bottlebrush statistical copolymers (Sci. Adv. 2020). I have also demonstrated a universal approach to photo-crosslink bottlebrush polymers by formulating a generic network model that predicts the moduli of UV-cured elastomers with improved sensitivity for capacitive pressure sensors (Macromolecules 2020). My Ph.D. work focused on connecting the mechanical performance of conjugated polymers with microstructural insights via fundamental polymer physics, including glass transition phenomena, chain entanglement, and liquid crystalline ordering. I first developed a rheological method to unambiguously determine the glass transition temperature (T_g) of conjugated polymers (Macromolecules 2017). Then, inspired by group contribution theory, I experimentally verified a novel model that quantitatively predicts T_gs from the chemical structure of conjugated polymers with different backbones and alkyl sidechains (Nat. Commun. 2020). Further rheological studies on the viscoelasticity of conjugated polymer melts led to the discovery of a new phenomenon related the local chain alignment in a liquid crystalline phase, which reduces entanglements (Macromolecules 2018). Both the glass transition temperature and chain entanglements dictate the stretchability of polymeric materials, so my work has made substantial contributions to guide the molecular design of conjugated polymers in ways that achieve desired mechanical performance (Adv. Electron. Mater. 2018). Combining my background in these fields with expertise in rheology and 3D printing, I believe my proposed research program in designing, characterizing, and prototyping stretchable conductors and mesogen-free nematics for biomedical and optical applications are truly unique and promising.

Teaching Interests:

I value teaching/mentoring as an integral and rewarding part of the professorship. Instead of merely passing textbook knowledge to students, I aim to inspire them to become self-motivated individuals who actively tackle real-world challenges in a collaborative and interdisciplinary environment. From my own experiences as a student, teaching assistant, and lecturer, I embrace the teaching philosophy of student-centered, inquiry-based, independence-interdependence-balanced, and application-inspired learning to achieve this goal. Creating a casual atmosphere that facilitates students’ participation and collaboration from diverse backgrounds, arousing students’ curiosity to explore new ideas, encouraging students to persevere, and providing adequate guidance on an individual basis is critical to students’ learning. I also believe that teaching/mentoring experiences will benefit me greatly as an advisor and educator. Refreshing fundamental knowledge by teaching can sometimes illuminate ongoing research with new ideas and continuously improve lecturing skills for audiences with different backgrounds.

My ultimate goal for teaching is to help students succeed beyond coursework. Looking back at my undergraduate research experience at the University of Minnesota, I will highly recommend my students to participate in research projects, put their knowledge into practice, master technical skills, and most importantly, discover their passion for science. Additionally, by presenting their work in either a university-wide exhibition or national/international conference, students will develop scientific communication skills and professional networks, which may further advance their careers in academia. As a Ph.D. student at Penn State, I was fortunate to have mentored two outstanding undergraduate students and one graduate student for about two years. Each had an individual project and has contributed to published work. As an advisor, I will also actively recruit undergraduate students to explore completely novel ideas, which could later turn into well-developed projects and open up new research avenues. Furthermore, I will keep an open-door policy for all undergraduate/graduate researchers to freely drop by my office and discuss project updates. I believe in the student-centered mentoring strategy, which requires me to match students’ interests and talents with suitable research projects and adjust between hands-on and hands-off styles according to their self-motivation, personality, and research progress.

With dual bachelor’s degrees in chemical engineering and materials science & engineering, a doctoral degree in chemical engineering, and a high school diploma in the U.S., I am confident in my abilities to teach a wide range of courses at both the undergraduate and graduate levels level. My preference list includes Polymer Physics, Rheology, Thermodynamics, Transport Phenomena (or Fluid Mechanics), Introduction to Materials Science and Engineering, and Materials Properties Lab. Besides supporting the department’s current curriculum and programs, I would like to design a graduate-level course entitled “Physical Properties of Polymers”. My background in polymer physics and various types of polymers — including conjugated, bottlebrushes, polyelectrolytes, and vitrimers — will provide students with an overall picture of the vibrant field of polymer research, as well as broaden students’ horizons on emerging applications. In summary, I am ready to make a positive influence on teaching and learning both inside and outside the classroom and excited about the opportunity to share my passion and knowledge with the next-generation scientists and engineers.