Ung Su Choi

The color change of polyacrylonitrile microspheres with thermal treatment temperature, and their positive- and negative-electrorheological behaviors.

Inspired by electrophoresis separation techniques of biomolecules, we have developed the methods for the preparation of negative and positive electrorheological materials.

To enhance the flexural strength of degradable expanded polystyrene (DEPS) while maintaining degradability, during the manufacturing processes of DEPS, cerium(III) stearate (CeSt₃) and poly‐L‐lactide (PLLA)/poly(butylene adipate‐co‐terephthalate) (PBAT) are used as a nontoxic oxidizer and a co‐biodegradable polymer filler, respectively. The flexural strength of DEPS is decreased by the oxidizer and increased by the biodegradable polymers. Furthermore, by favorable interfacial interaction between PLLA and PBAT, the flexural strength is more enhanced when the two biodegradable polymers are used simultaneously than used separately. The photo‐, bio‐ and oxo‐degradation behaviors of DEPS were evaluated by UV irradiation, thermal treatments, landfill, and non‐landfill tests. Molecular weight of our DEPS is decreased to 90.26% after 2 weeks of UV irradiation and 74.4% after 3 months of thermal treatment test. 35.4 and 31.4% of weight of our DEPS is reduced after 3 months of landfill and non‐landfill test. It is confirmed that the decomposition period of DEPS could be adjusted by controlling the amount of the oxidizer and/or the biodegradable polymers. The FT‐IR study demonstrated that oligomers and nonylphenol which are known to cause the environmental hazards are not generated after the degradation of DEPS. POLYM. ENG. SCI., 57:883–890, 2017. © 2016 Society of Plastics Engineers

Printing electronic components on a chip edge and a stepped substrate with functional inks are an attractive approach for achieving flexible and inexpensive circuits for applications such as flexible displays and large-area chemo/bio/radioactivity sensors. However, it is still challenging because a sufficient cover of the 100 μm high step at the chip edge with a high-resolution pattern is the hardest part of the layer assembling by inkjet printing. Herein, we present a simple and effective strategy to generate electrically conductive line-patterns on stepped substrates by applying the DC electric field. On the surface of flat polyimide substrate, the fine line-pattern (less than 850 nm in line width) is achieved with a polyaniline coated MWCNT dispersed ink. Furthermore, 9.9 μm of line width is successfully patterned on the high stepped poly(dimethylsiloxane) substrate, higher than 100 μm, by printing only 1 time.

Herein, the mixing effect of amine and carboxyl groups on electrorheological (ER) properties has been presented with the chitosan and alginic acid dispersed suspensions. Chitosan (for the amine group) and alginic acid (for the carboxyl group) are used to investigate the mixing effect of the amine and carboxyl groups on ER properties with the control of their mixing ratio in the silicone oil. The surface-chemical structure of the mixture of the chitosan and alginic acid particles in the silicone oil is demonstrated by in situ Fourier transform infrared (FT-IR) spectroscopy at various electric fields for the first time. This study focuses on whether the mixture of chemical groups in the ER fluid can promote ER properties or not, and in situ FT-IR analysis of the interface between ER particles in the silicone oil at various DC electric fields. The ER fluids exhibited the increase of the yield stress values with the increase of the counter group addition up to the weight ratio of 50 : 50 (chitosan : alginic acid). A noteworthy result is that the mixing effect of the amine and carboxyl groups resulting in enhanced ER properties is clearly proved. In the in situ FT-IR study, the complex form of amine and carboxyl groups of particles in the ER fluid was confirmed under the electric field.

Herein, the electrorheological (ER) properties of highly dispersion-stable, biocompatible and biodegradable chitosan derivative dispersed ER suspensions are explored. Electro-mechanical responses of the ER suspensions are enhanced with fixed spacers (amide and ester groups) and various functional groups (acid series and their complex forms with urea). A noteworthy result is that the shear stress of urea complexed chitosan acid dispersed suspensions was higher than before doping the urea molecule. However, urea complexed chitosan phosphate and sulphate showed a decreased tendency of shear stress due to too high conductivity at the high temperature. In the dispersion stability test, the chitosan dispersed suspensions showed high dispersion stability for long times. The study of the influence of dipolar molecules on the ER properties of the chitosan derivative dispersed suspensions under an electric field shows how to enhance the ER responses easily just by doping molecules.