(6hs) Structure and Design of Soft Materials for Stretchable Electronics

Soft materials, such as polymers, have shown considerable potential in a wide range of electronic applications, including light-weight, flexible organic field-effect transistors (OFETs), organic photovoltaics (OPVs), and organic light-emitting diodes (OLEDs). Although current electronics using rigid silicon-based components provide outstanding performance, there is growing demand for the next generation of organic electronics that is deformable and stretchable. Polymers are promising materials enabling both high electrical performance and intrinsic stretchability. Thus, the primary aim of my research is to design polymeric materials with mechanical and conductive properties and develop their structures for stretchable electronics (e.g., artificial muscles, electronic skins). As a basic unit in electronics, OFETs have attracted a significant amount of academic and industrial research attention over the past three decades. To realize the high performance of stretchable OFETs, the polymer materials can be served as two parts (i.e., channel, dielectric layers). First of all, semiconducting polymers as channel materials (i.e., conjugated polymers) have experienced huge developments in the fields of OFETs. As an example of the developments, the alkyl side chains of these conjugated polymers are no longer considered as solubilizing groups, but as key players that can have a profound impact on the molecular packing density and electronic performance. Furthermore, the stretchability of the conjugated polymers depends on the length and size of the side-chains, and thus the design of conjugated polymers play an important role in the development of stretchable electronics. The polymer materials can also contribute to stretchable and mechanically robust dielectrics. Recently, the use of polymer electrolytes as dielectrics has attracted growing attention due to a low voltage operation and electrochemical properties. In particular, the polymer electrolytes are electronically insulating, but ionically conductive so that they are applicable as stimuli-driven materials. Therefore, the polymer electrolytes are significantly attractive for more diverse stretchable electronics (e.g., sensors, actuators) beyond organic transistors.

As described, polymers have significant potential to serve the next generation of stretchable organic transistors with improved performance. However, polymer-based stretchable electronics still remain challenging to be commercialized, because they have a rigid polymer backbone that potentially limits the elastic stretchability, and are highly susceptible to damage from environmental conditions. In order to establish the environmentally stable and mechanically stretchable polymer electronics, my career objectives will focus on three specific research efforts: (1) designing the environmentally stable conjugated polymers and evaluating the impact of molecular architectures by X-ray characterization, (2) developing the polymer electrolytes as dielectrics and elucidating the relationship between molecular structure and ionic properties, and (3) investigating a polymer composite material consisting of two or more components and illustrating the interfacial structure for stretchable organic transistor applications. Because extrinsically stretchable polymer composites will present another great opportunity that cannot be fulfilled by a single material as well as the rational design of intrinsically stretchable polymers. Beyond the macroscopic investigation by microscopes (e.g., scanning electron microscopy (SEM), atomic force microscopy (AFM)), the nanoscopic characterization by X-ray scattering will be employed for the information of these polymers such as molecular packing density, degree of crystallinity and orientation of domains. In addition to my three primary areas, my future research interest involves the development of sensors, actuators, and skin electronics system with various functionality.

Research Experience:

My research at both Seoul National University (Mentor: Professor Kookheon Char) and Purdue University (Mentor: Professor Bryan W. Boudouris) has involved the design of soft materials and their integration into next-generation flexible electronic devices. In brief, I have focused on: (1) determining the impact of nanostructure in phase-separated organic memory diodes in order to advance flexible logic circuits; (2) utilizing interfacial engineering with radical polymers in organic field-effect transistors for enhanced device performance; (3) and elucidating the charge transport mechanism of radical polymers in order to generate ambipolar, transparent thin film transistors. As a graduate student, I have a significant amount of experience with respect to the design, fabrication, and optimization of organic electronic devices. Moreover, I have been able to utilize these devices to probe the fundamental physics of charge transport in a unique and emerging conducting polymer system (i.e., open-shell macromolecules).

I intentionally switched from more synthetic and device-focused work during my graduate work to a research position that is centered on polymer physics during my postdoctoral career at University of Delaware (Mentor: Professor Thomas H. Epps III). Currently, my work mainly involves the design, synthesis, and nanoscale characterization of macromolecules for integrated electronic circuit configurations. Particularly, I am focusing on the behavior of fluorinated block polymers and the control of nanoscale morphologies using a straightforward solvent vapor annealing (SVA) process

Thus, my work to date has focused on bridging nanoscale scientific phenomena to device engineering at the macroscale, and I anticipate utilizing this previous experience to launch my own research group in order to impact the realms of flexible and stretchable electronics in the near future.

Teaching Interests:

Aside from my research career, I also have considerable teaching experience and have previously served as a teaching assistant for undergraduate courses in Engineering Mathematics, Transport Phenomena, and Design of Staged Separation Processes. This previous experience has allowed me to instruct some of the core, fundamental courses in chemical engineering at my previous institutions of Seoul National University and Purdue University. I was able to gain a deep insight into how to instruct undergraduate students in the fundamentals of chemical engineering from some of the most respected instructors in the field (e.g., Professor Phillip Wankat at Purdue University). Specifically, I delivered lectures for students, held regular office hours, and developed course materials. Thus, I can contribute to delivering any courses in the core chemical engineering curricula and more specific electives, such as polymer chemistry and organic electronics. Additionally, I participated in the mentorship for undergraduate students as a part of their undergraduate thesis at Seoul National and Purdue. Based on my previous experiences, I am more than ready to lead the new generations of students to the high level of learning and training.