Do Sung Huh

Studies on Properties of Polyaniline-Dodecylbenzene Sulfonic Acid Composite Films Synthesized Using Different Oxidants

Two types of nano composite were obtained byin situ chemical method in polyaniline (PANI)/dodecylbenzenesulfonic acid (DBSA) system depending on the use of either ammonium persulfate (APS) or ferric chloride (FeCl3) as the oxidant. In order to study the difference of the two composites in the surface characteristics, thermal stability, and electric properties, the composite films were studied by transmission electron microscopy (TEM), X-ray diffraction (XRD), thermogravimetric analysis (TGA), and temperature dependent DC electrical conductivity. The results revealed a large difference in the surface morphology, thermal stability, and the microstructure properties between the two composites, and these differences were considered responsible for the molecular order and conductivity.

Characterization and electrochemical behaviors of honeycomb-patterned poly(N-vinylcarbazole)/polystyrene composite films

Poly(N-vinylcarbazole)/polystyrene composites were prepared through simple radical polymerization of N-vinylcarbazole in the presence of polystyrene. Honeycomb-patterned composite thin films were fabricated by casting the composite solutions under humid conditions. The scanning electron microscopy (SEM) images of the resulting honeycomb pattern on the composites show a higher regular structure compared to those of films prepared from the poly(N-vinylcarbazole) homopolymer. The pressure-area isotherms and photoelectrochemical behaviors of the patterned films were also observed. The photoconductivity of the patterned thin films increased with increasing poly(N-vinylcarbazole) concentration. This enhancement is attributed to the effects of the honeycomb structures and the charge transfer across the donor/acceptor hybrid interface in the composite films.

The Revival Wave Induced Spontaneously in a BZ-Type Mixture

We have examined the unusual behavior of wave propagation in the BrO3- - 1,4- cyclohexanedione - ferroin reaction system. Two patterns of traveling wave have been induced spontaneously with long time lag in the reaction process. A new wave has been induced as a concentric pattern after an initially induced wave has disappeared. The initially induced wave shows an irregular spiral pattern with a high wave frequency. The two waves show very different behavior in the pattern and in other wave characteristics as well. We compared the behavior of the two waves and suggested an appropriate reaction process for unusual behavior of wave propagation in the system by considering the reaction intermediates of the organic compounds.

The influence of visible light on the formation of revival waves in the 1,4-cyclohexanedione–bromate–ferroin reaction

Revival waves, which emerge spontaneously long after the oscillatory bromate–1,4-cyclohexanedione–ferroin reactions become quiescent, are found susceptible to the illumination of visible light. Depending on the intensity and the duration of the light perturbation, an illumination can drive the system either to a reduced reaction state with a high concentration of ferroin, or to an oxidized state with a high concentration of ferriin. When hydroquinone, a main product from 1,4-cyclohexanedione oxidation, is used to gradually replace 1,4-cyclohexanedione as the reductants, the induction period of the formation of revival waves is shortened significantly; however, there is no clear difference in their photosensitivity. These new experimental results suggest that the observed photosensitivity is determined by the photochemistry of the products of hydroquinone.

Photo-controlled bifurcations in the 1,4-cyclohexanedione-hydroquinone-bromate-ferroin reaction

Abstract The 1,4-cyclohexanedione/hydroquinone/BrO 3 − /ferroin reaction system is uncovered to exhibit photo-controlled oscillatory reaction dynamics, in which illuminations with visible light can either induce or inhibit chemical oscillations. The observed behavior exhibits strong dependence on the wavelength of the incident light and the initial concentrations of hydroquinone and the metal catalyst ferroin. A possible photo-reaction path is suggested on the basis of experimental observations.

Morphology and electrical properties of poly(3,4-ethylenedioxythiophene)/titanium dioxide nanocomposites

Poly(3,4-ehtylenedioxythiophene) (PEDOT) nanocomposites including nano-sized titanium dioxide were prepared by in situ polymerization technique and were characterized by Fourier transform infrared (FTIR) and UV-visible spectroscopy. Morphological studies of the nanocomposites were performed using scanning electron microscopy and transmission electron microscopy to support the formation of PEDOT-TiO2 nanocomposites. Results suggested that the TiO2 nanoparticles were well-dispersed in the PEDOT polymer matrix. The electric properties of the nanocomposites were obtained by measuring the temperature-dependent direct current (DC) conductivity between 300 and 500 K and low frequency alternate current conductivity between 0 and 10 kHz. The PEDOT-TiO2 nanocomposites exhibited remarkable improvement in the temperature-dependent DC conductivity with decreased dielectric constants and dielectric losses, compared to pure PEDOT polymer, which indicates their higher ability to store electric potential energy under the influence of an alternating electric field.

Reversible adsorption-desorption oscillations of nanoparticles on a patterned hydrogel surface induced by a pH oscillator in a closed chemical system

Oscillatory adsorption-desorption of Ag nanoparticles on a pH-responsive hydrogel surface was induced by a pH oscillator in a closed reaction system. The hydrogel surface was prepared as a honeycomb-patterned film using a honeycomb-patterned polystyrene film as a template to speed up the response time in the stimuli-responsive hydrogel. The surface morphology and hydrophobic interaction of the patterned hydrogel surface were significantly altered by the pH change of the aqueous solution that came into contact with the gel. The surface of the hydrogel became hydrophobic for adsorption in a lower-pH solution but became hydrophilic with decreased adsorptivity at higher pH conditions. A closed system chemical pH oscillator composed of CaSO3-H2O2-NaHCO3-H2SO4 was applied to force the periodic adsorption-desorption of Ag nanoparticles on the gel surface. The experimental conditions for the chemical oscillator were optimized to obtain long-lasting high-amplitude pH oscillations in a closed reactor. The periodic adsorption-desorption was proved to be induced by the periodic pH change in the solution, although the two phenomena were not completely synchronized. That is, the periodic time was longer and the number of oscillations was less for the adsorption-desorption compared with the pH oscillations that occurred in the solution state. However, the heterogeneous oscillations obtained in this study clearly suggested that the hydrophobic interaction was reversibly changed in the patterned pH-responsive hydrogel surface, similar to various biological systems in nature.

Graphene oxide incorporated poly(ε-caprolactone) honeycomb-patterned porous polymer films by the breath figure method

Poly(ε-caprolactone)-graphene oxide (PCL-GO) honeycomb-patterned films were successfully fabricated by breath figure method for the first time by the simple blending of individual components in a water miscible solvent, tetrahydrofuran. PCL-GO films were reduced using sodium borohydride to obtain PCL-reduced graphene oxide (PCL-rGO) films. The films were characterized by their color, thermogravimetric analysis (TGA), scanning electron microscopy (SEM), and X-ray photoelectron spectroscopy (XPS). TGA result shows the improvement of the thermal properties of PCL by the incorporation of GO. The SEM image shows the formation of monodispersed porous honeycomb-patterned PCL-GO films, and these patterns are retained after the reduction of GO to PCL-rGO without any wreckage. The reduction of GO to rGO was confirmed from the color of the films and from the XPS analysis. The present methodology is expected to widen the use of breath figure technique to achieve a wide variety of functionalized films by simple blending using water miscible solvents, which would otherwise not be possible using water immiscible solvents.

Effect of UV illumination on the fabrication of honeycomb-patterned film in the photo-responsive poly(methylmethacrylate/azobenzene) copolymer

A photoresponsive poly(methylmethacrylate/azobenzene) copolymer was synthesized through the copolymerization of methylmethacrylate (MMA) with 6-[4-(4-dimethylaminophenylazo)phenoxy]-hexyl methacrylate (Azo-monomer) to see the effect of UV illumination on the formation of honeycomb-patterned films fabricated by casting the copolymer solution under humid conditions. The synthesized copolymer was characterized by Fourier transform infrared, UV-vis, and nuclear magnetic resonance spectroscopy. The honeycomb-patterned films obtained by UV illumination showed more highly ordered films. It is due to a photo-switched isomerization of the azobenzene component in the PMMA-Azo copolymer from trans- to cis-isomer, which induces the amphiphilicity of the copolymer solution by increased dipole moment.

Characterization and electrical behavior of biodegradable poly(N-vinylcarbazole)/poly(3-hydroxybutyric acid) composite films

AbstractPoly(N-vinylcarbazole) (PVK) composites containing poly(3-hydroxybutyric acid) (PHB) were synthesized via in situ deposition. The oxidative polymerization of N-vinylcarbazole was carried out by dissolving different weight percentages (10, 20, 30, 40, and 50 wt%) of PHB using ferric chloride as an oxidant. The as-synthesized composites were characterized by Fourier-transform infrared spectroscopy and X-ray photoelectron spectroscopy. The surface morphology of the resulting composites was studied by transmission electron microscopy, and the biodegradability of the composites was tested by the Sturm method. The temperature-dependent DC conductivity of the synthesized composite films was measured, and the activation energy responsible for the conductivity was examined. The incorporation of PHB in the synthesis of PVK composites significantly increased the conductivity and biodegradability of the resulting products. Thus, the newly synthesized composites have potential applications in the biological, medical, and engineering fields.