Chul Jae Lee

Surface-enhanced Raman spectroscopy of Omethoate adsorbed on silver surface

We have investigated surface-enhanced Raman spectroscopy (SERS) spectrum of Omethoate (O,O-dimethyl-S-methylcarbamoylmethylthiophosphate). It is found significant signals in the ordinary Raman spectrum for solid-state Omethoate as well as strong vibrational signals absorbed on the silver sol surface which is prepared by γ-irradiation technique at a very low concentration. Effects of pH and anions (Cl-, Br-, I-) on the adsorption orientation are investigated as well. Two different adsorption mechanisms are deduced, depending on the experimental conditions. The sulfur atom or the sulfur and two oxygen atoms are adsorbed onto the silver sol surface. Among halide ions, Br- and I- are more strongly adsorbed onto the silver sol surface. As a result, the adsorption of Omethoate is less effective due to their steric hindrance.

Highly Proton Conductive Poly(vinyl acetate)/Nafion® Composite Membrane for Proton Exchange Membrane Fuel Cell Application

A novel blend of membranes made of cast Nafion® and poly(vinyl acetate) (PVAc) was prepared and its proton conductivity and ion exchange capacity (IEC) were characterized to investigate its applicability in proton exchange membrane fuel cells (PEMFCs). The intermolecular interactions and morphology of these membranes were assessed using Fourier-transform infrared spectroscopy (FT-IR) and field-emission scanning electron microscopy (FE-SEM). A twofold increase in the proton conductivity is observed for the PVAc/Nafion® composite membrane (2 × 10-2 Scm-1) compared to that of cast Nafion® (1.1 × 10-2 Scm-1). In addition to that, the composite membranes exhibited better mechanical strength and adequate water retention ability as well as IEC comparable to that of cast Nafion®. The thermal property and chemical degradation property were also investigated. The results indicate that the introduction of PVAc as a modifier played a vital role in improving the membrane performance. Accordingly, these polymer electrolyte membranes with suitable PVAc contents have prospect for use in low-temperature PEMFCs.

Conducting polyaniline-rutile TiO2 nanocomposites for the development of high-k dielectric materials

ABSTRACT Inorganic dielectrics encapsulated in an organic matrix are showing excellent promise as novel dielectric materials. In this work, firstly highly organized crystalline nanoparticles of rutile TiO2 were synthesized by acid hydrolysis of titanium isopropoxide at room temperature. Then we developed a novel dielectric material consisting of highly organized rutile TiO2/polyaniline (PAni) nanocomposites by in-situ chemical oxidative polymerization. The structural, morphological, conducting, and dielectric properties of the rutile TiO2/PAni nanoparticles have been evaluated by X-ray diffraction (XRD), scanning electron microscopy (SEM), high resolution-transmission emission microscopy (HR-TEM), four-point probe technique, CV (Capacitance versus Voltage), and Impedance analyzer. The nanocomposites show 70 times higher permittivity compared to rutile nanoparticles and much higher compared to anatase/PAni (ES) nanocomposites at 10 MHz. Large interfacial polarizations, nanostructure, and dopant levels are the key factors for the large dielectric constant of the nanocomposites. The rutile/PAni (ES) nanocomposites might see potential uses in super-capacitors, gate dielectric in transistors, and capacitive-type gas sensors.

Physical and Antibacterial Properties of Gold-Poly(ethyl methacrylate) Nanocomposites Prepared by In-Situ Polymerization.

In this paper, the physical and antimicrobial properties of gold-poly(ethyl methacrylate) nanocomposites (Au-PEMA) are evaluated. Characterization of gold nanoparticles was carried out based on UV-Vis spectroscopy and transmission electron microscopy (TEM). The specimens were characterized by attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR), thermal gravimetric analysis (TGA), differential scanning calorimetry (DSC), and field emission scanning electron microscope (FE-SEM). We identified the thermal stability of Au-PEMA nanocomposites and the inhibitory effect of live bacterial attachment of Au-PEMA nanocomposites against S. mutans was also evaluated.

Characterization of Silver Nanoparticles Incorporated Acrylic-Based Tissue Conditioner with Antimicrobial Effect and Cytocompatibility

Tissue conditioners are readily degradable and microbial colonization and biofilm formation on those surfaces may cause denture-induced stomatitis or respiratory infections. The modified tissue conditioner combined with silver nanoparticles was fabricated and characterized to develop a novel antimicrobial gel polymer with its biological compatibility. In antimicrobial activity, tissue conditioner containing 0.1% of Ag° displayed minimal bactericidal effect against Staphylococcus aureus and Streptococcus mutans , 0.5% Ag° loading revealed minimal fungicidal effect for Candida albicans ( P <0.01). The cytotoxicity of the extracts from samples was measured by MTT assay and up to 0.5% of Ag° incorporation showed excellent cell compatibility to human gingival fibroblast cells. The results suggest that Ag° loaded tissue conditioner could be a possible candidate for a novel antimicrobial denture material with uncompromised cytocompatibility.