(7cs) Metallurgy-Mimic Thermal Processing and Morphology of Particle-Forming Diblock Copolymers

Low-symmetry phases including the dodecagonal quasicrystal and tetrahedral close-packed Frank-Kasper σ phase recently have been identified in various forms of soft materials including dendrimers, surfactants, and block polymers. In block polymers these complex phases emerge from the supercooled fluctuating disordered state, comprised of well-formed micelles. Rapid cooling to sufficiently low temperatures below the order-disorder transition extinguishes molecular exchange resulting in non-ergodic “liquid-like packing”. Here we present yet another family of the Frank-Kasper phases obtained as a function of temperature and time from polyisoprene-b-polylactide (PI-b-PLA) diblock copolymers containing 15 to 20% PLA, utilizing small-angle X-ray scattering as a probe. The development of distinct periodic or aperiodic states depends on how specimens are cooled from the disordered state to temperatures below the order-disorder transition temperature. Whereas direct cooling leads to the formation of previously documented morphologies, rapidly quenched samples that are then heated from low temperature form the hexagonal C14 and cubic C15 Laves phases commonly found in metal alloys. Self-consistent mean-field theory calculations show that these, and other associated Frank-Kasper phases, have nearly degenerate free energies, suggesting that processing history drives the material into long-lived metastable states defined by self-assembled particles with discrete populations of volumes and polyhedral shapes.

Research Interests: Structure-property relationship of block copolymers, polyolefins, and functional polymer materials

I earned a Ph.D. in Polymer Chemistry at Pohang University of Science and Technology (POSTECH), South Korea. My Ph.D. work was mainly evaluating structure-property relationship of thin-film polymer electronic materials. The study has familiarized me with (i) polymer chemistry and physics, (ii) characterization of thermal, mechanical, and electrical properties of functional polymers, and (iii) synchrotron X-ray techniques such as X-ray scattering, reflectivity, and spectroscopy, along with fundamental theories governing such techniques. My current research as a postdoc involves two very different projects. One aims to reveal the underlying principles of microphase separation in sphere-forming block polymers at equilibrium and non-equilibrium conditions (which will be presented here). The other focuses on interfacial properties of commercial polyolefin blends and multilayer films. These projects rely on the integration of polymer synthesis and molecular characterization, synchrotron X-ray scattering, rheological characterization, and imaging techniques such as scanning electron microscopy (SEM) or transmission electron microscopy (TEM).

I enjoy learning any theories or techniques that help further my understanding of nature, and proving their validity. Also, I am willing to find fundamental ideas that govern complex natural phenomena. Thus, I would like to pursue my next career as a faculty member in research institution. My future research interst lies on several aspects. The most insteresting theme would be the study of complex phase formation in simple block polymer systems. My synthesis and characterization skills for the model block polymers will enable extensive research on particle-forming phase portrait of the system and investigation to find governing principles of such complex phase formation. Diblock copolymers are an obvious candidate, but the research can be extended to relevant systems (e.g., multiblock polymers). My research interest also includes interfacial phenomena occurring in polyolefins and polymers having functional groups that have potential application for electronic thin film devices.

Teaching Interests: With my expertise in X-ray scattering technique, I can teach courses such as Structure of Materials or X-ray Scattering/Diffraction/Crystallography. My solid knowledge of basic polymer science enables me to teach Polymer Chemistry, Polymer Characterization or Polymer Physics. Furthermore, thanks to my educational background as a chemist, I can teach chemistry-related core undergraduate courses for materials science or chemical engineering students, such as Physical Chemistry or Instrumental Analysis.

Relevant Work: Kyungtae Kim, Morgan W. Schulze, Akash Arora, Ronald M. Lewis III, Marc A. Hillmyer, Kevin D. Dorfman, Frank S. Bates, Thermal processing of diblock copolymer melts mimics metallurgy, Science 2017, 356, 520-523. DOI:10.1126/science.aam7212 (K.K., M.W.S., and A.A. contributed equally)