Research

Block copolymers (BCPs) can self-assemble into various nanostructures by microphase separation. Typically, the domain size is in the range of 10 - 100 nm. This property can be suitable for many practical purposes such as data storage, (photo)lithography augments, nanowire fabrication, nanoparticle deposition, membrane, or optical metamaterials. For such applications, the microdomain size should be manipulated to guide the orientation of nanostructures by means of pre-patterned substrate, external fields or interface design.

Physical properties of polymer films are significantly affected by the interfacial interactions with the adjacent surfaces. Glass transition temperature (Tg), thermal expansion coefficient (CTE), order-disorder transition (ODT), and wetting/dewetting behavior of polymer films are closely related to the affinity of substrate toward the polymer films. We are particularly interested in the autophobic dewetting (chemically identical PS brush repels PS film) phenomena and the thermal behavior of polymer films on both preferential/nonpreferential substrates. Understanding the fundamental polymer physics at the interface is highly important not only for scientists, but also for designing nano-devices and its applications. 

Unlike the phase transitions in the bulk BCPs, the order-disorder transition temperature in film geometry is influenced by interfacial interactions such as preferential and neutral substrates. Such tendency becomes outstanding when film thickness decreases. For the further application of nanostructure-dependent polymer thin film devices, understanding the structural transition behavior is very important. Our group take advantage of the ultra small angle x-ray scattering technique in order to prove the effect of interfacial interaction on transition behavior experimentally. Recently, we carried out a collaboration study with the SCFT simulation by Jaeup U. Kim group, UNIST, Korea.

Small-angle X-ray scattering (SAXS) a reliable and super-accurate analysis technique which is based on the elastic scattering of X-ray (wavelength of 0.1 ~ 0.2 nm) caused by inhomogenieous samples. It is very useful to analyze nanoscale periodic structures (i.e. block copolymer) having electron density difference among the constituent domains. Our group actively takes advantage of not only the transmission SAXS for bulk polymers, but also the grazing-incidence SAXS (abbreviated to GISAXS) for polymer thin films.

Polymer baroplasticity is a desirable property for the recycling and regenerating material industries, since it allows the polymers to flow at relatively mild pressure. Particularly in baroplastic block copolymers (BCPs), the compressibility issue pertaining to the enhanced miscibility with pressure has been an attractive topic, because an ordered state of baroplastic BCPs becomes a phase-mixed (or disordered) phase between the two dissimilar blocks upon pressurizing. Our group has reported the characteristic phase behaviors of baroplastic BCPs and their blends.