We currently work on two research topcis (i) Phase Behavior of Polymers and Related Materials and ii) Ion-containing Polymers.

 

Phase States and Phase Transitions of Polymer and Polyaromatic Hydrocarbon Mixtures

Polyaromatic hydrocarbons (PAHs) have unique physical properties useful in designing self-assembling materials, organic electronics, and optical applications. PAHs are naturally occurring from combustion processes and also abundant in crude oils, coals, and even the universe. However, their delocalized π electrons and planar molecular structures make PAHs highly immiscible with other classes of materials, and controlled blending of PAHs with other materials is often challenging. We are investigating the phase behavior of polymers and PAHs to understand the molecular structural factors governing the miscibility between PAHs and polymers.

We realized the characterization of the phase behaviors of mixtures of polymers and small PAHs can be conveniently conducted using differential scanning calorimetry (DSC), and even the DSC characterization can simultaneously extract the composition of polymer-rich phase. We chose pyrene as a representative PAH compound and investigated the phase behavior of pyrene and model polymers. This work is reported in Gagan N. Kangovi, Sangwoo Lee, "Phase Behavior of Pyrene and Vinyl Polymers with Aromatic Side Groups" publsihed in Macromolecules.

We are currently investigating the phase separation behaviors relevant to destabilizations of multicomponent mixtures using polymer and PAH compounds to find a way to control the phase separation process.

 

Block Copolymer-based Fuel Cell Membranes

Fuell cell technology directly converts chemical energy to electricity. Fuel cell technology has many advantages in storage and transportation of energy; and energy density compared to battery technology, which is competing and complementary energy technology to fuel cells. Fuel cell technology is also highly desirasble technology in terms of energy sustainability and renewability.

One challenge in the fuel cell technology is the preparation of cost-competitive and high-performance polymer electrolyte membranes with excellent thermal and chemical stability. We believe judiciously designed block copolymer materials can be one of the solutions for cost-competitive and high-performance polymer electrolyte membranes. We are actively working to identify key relationships between chemical motifs and microstructures of polymer electrolyte membranes for the development of new class of block copolymer-based fuel cell membranes.

 

Precisely Tailored Ionomers

Ionomers are polymers containing a small amount of ionic groups in non-ionic polymer chains. The ionic groups in non-ionic polymer matrix strongly interact with each other and result in interesting structures and properties for various applications and scientific interests. However, placing ionic groups precisely at target locations in chains is challenging.


We are currently establishing a new synthetic strategy to prepare precisely tailored ionomers that will open new opportunities to tune the structures and properties of ionomers.

 

Block Copolymer Micelles on Close-Paked Structures

Close-packed structures of equal spheres mean the crystal structures with the highest volume fraction of spherical particles. Although this notion regarding the highest volume fraction was first speculated by Johanness Kepler in the 17th-century, but it took nearly four centuries until it was formally proven by Thomas Hales in 1998.

Another interesting point of the close-packed structures is that we can imagine infinite number of close-packed structures, and it was another big argument which close-packed structure is the most stable one. In 1997, the face-centred cubic structures was claimed more stable than the hexagonally close-packed structures, and later the face-centered cubic structure was calimed most stable among all possible close-packed structures. However, people have identified other close-packed structures from diverse material classes.

We recently discovered block copolymer micelles crystallizing from a fluid-like state to face-centered cubic structures develop intermediate hexagonally close-packed and random stacking of hexagonally close-packd layers of block copolymer micelles. This finding suggests possible origins of the non-face-centered-cubic close-packed structures of equal spheres occurring in nature.