Hee-Taik Kim

Investigation of shape controlled silver nanoplates by a solvothermal process

The shape control and growth process of silver nanoplates formed by a solvothermal solution approach was investigated by placing a mixed solution containing silver nitrate, poly(vinyl pyrrolidone) (PVP), N,N-dimethylformamide (DMF) or ethanol in an autoclave and examined the products under various reaction conditions. The formation process in ethanol proceeds slowly taking more than 10h to form a suspension of hexangular single plates, which are no more than 50nm in edge length, while the process in DMF is relatively rapid forming large single plates within 2-4h. These separate nanostructures can be fused extensively toward the edge region to form a larger mass. The different sized plates fused together grew to large films or belts but maintained the same thickness. Apart from the reaction time and temperature, appropriate amounts of PVP and DMF were also found to be critical to the shape control. Relatively small triangular plates with average edge lengths of 20-50nm could be separated easily from the product. UV-vis absorption spectroscopy showed that these nanoplates exhibit a strong absorption band from 470 to 630nm. Compared with other methods, our synthesis is mass-productive, rapid and easily operated. The newly formed silver nanoplates may have many potential applications in the biological, chemical, and electrical industries.

Transport phenomena in gas permeation through glassy polymer membranes with concentration-dependent sorption and diffusion parameters

The modified dual-mode mobility model for permeation of a gas in glassy polymer membranes was combined with the extended dual-mode sorption model to take account of the plasticization effect of sorbed gas molecules on both sorption and diffusion processes. The combined model was further simplified by the introduction of a concentration of the mobile gas species. However, the observed pressure dependence of mean permeability coefficients of carbon dioxide in methylmethacrylate-n-butyl acrylate copolymer and polymethylmethacrylate films at 30°c and also that of oxygen in a polycarbonate film at 50°C and 60°C showed that a plasticization action of sorbed gas species has an influence on the diffusion process rather than on the sorption process, that is, were simulated by the modified dual-mode mobility model combined with the conventional dual-mode sorption model.

Transport of oxygen and carbon dioxide through polycarbonate membrane

Sorption equilibria and permeation rates for oxygen and carbon dioxide in polycarbonate membrane were measured at different temperature between 30 and 60°C and at pressures up to 2.5 MPa. The pressure dependence of mean permeability coefficient to oxygen obeyed the conventional dual-mode mobility model, whereas that to carbon dioxide followed a modified dual-mode mobility model with concentration-dependent diffusivities, as that of polystyrene to the same gas did.

Gas permeation through glassy polymer membranes with relatively low glass-transition temperature

When the glass-transition temperature of the polymer is not so much higher than the experimental temperature, the pressure dependence of the mean permeability coefficient of the poly-mer membrane to a gas is apt to deviate from the prediction by the conventional dual-mode mobility model, and to obey a similar model with concentration-dependent diffusivities because of the plasticization action of sorbed gas in the polymer membrane. In this work, sorption and permeation for oxygen and carbon dioxide in a membrane of polystyrene whose glass-transition temperature is 95°C, were measured to discuss the mechanism of gas diffusion in glassy polymer membranes with relatively low glass-transition temperature at 30, 40 and 50°C respectively.

Fabrication and Characterization of Ag Nanoparticle Dispersed Polymer Nanofiber and Ag Nanofiber Using Electrospinning Method

Functional nanomaterial is expected to have improved capacities on various fields. Especially, metal nanoparticles dispersed in polymer matrix and metal nanofiber, one of the functional nanomaterials, are able to achieve improvement of property in the electric and other related fields. In this study...

Oxidative regeneration of sulfided sorbent by H2S without emission of SO2

Much SO2, another perilous air pollutant, was emitted during the oxidative regeneration of sulfided sorbent by H2S. In order to prevent emission of SO2, we carried out oxidative regeneration with the physical mixture of CaO and sulfided sorbent and investigated the effect of regeneration temperature and oxygen concentration on the reactivity of CaO with S02. The effluent gases were analyzed by G.C. and the properties of sorbent were characterized by XRD. SEM, TG/DTA and EPMA. Deterioration of reactivity of CaO with S02 resulted in increment of emission of SO12 due to the structural changes of CaO above 750°C and that at 850°C was more severe. Furthermore EPMA and XRD analysis revealed that product layer diffusion through the solid product, CaSO4, was the rate limiting step for CaO sulfidation. The reaction of CaO w:.th SO2 was first order approximately and that was accelerated by high O2 concentration.

Structural characterization of the silver-polyaniline nanocomposite for electronic devices

Incorporation of metal nanoparticles in Polyaniline composites could effectively improve its optical, thermal and electrical properties and making it an ideal for the use in semiconductor industry. In this study Ag nanoparticles were uniformly dispersed ultrasonically in the solution of polyaniline emeraldine base (PANIEB) and isopropyl alcohol. PANIEB used in this experiment were doped with polymer of methacrylic acid ester and vinyl verstate. The results about the morphological, optical and electrical properties of Ag-PANIEB with IPA colloid as a function of different concentration of Ag nanoparticles (Such as 25%, 50%, 100% by weight) were presented and discussed.

Effect of sulfidation/oxidative regeneration cycle on the solid structural changes of sorbent for high-temperature removal of H2S

In order to investigate the effects of sulfidation/oxidative regeneration cycle on the change of structural properties and removal capacity of sorbent, sulfidation/regeneration cycle was carried out up to 15 times in a fixed-bed reactor. The effluent gases from the fixed-bed reactor were analyzed by gas chromatography, and XRD, SEM, and liquid nitrogen physisorption method were used to characterize the reacted sorbents. The sorbent treated first sulfidation/regeneration cycle exhibited maximum specific surface area and the highest H2S removal capacity. Hysteresis of adsorption isotherm of the regenerated sorbent reflected the growth of pores of fresh sorbent and pore size distribution confirmed this fact. Furthermore constant H2S removal capacity was maintained up to 15 times of sulfidation/regeneration cycle.

Bimodal dispersion of silver nanoparticles for conducting polymer

The effects of isopropyl alcohol (IPA) on the dispersion of bimodal silver nanoparticles inside polyaniline emeraldine base (Ag-PANIEB) as nanocomposite were investigated and discussed. Firstly, the bimodal Ag nanoparticles were synthesized with the help of precipitation method by semi-batch reactor and then ultrasonically blended inside the PANIEB matrix in the presence/absence of IPA followed by various characterization of Ag-PANIEB nanocomposite. It was observed that the bimodal dispersion of Ag nanoparticles inside PAIEB thin film was significantly improved in the presence of isopropyl alcohol (IPA). Such bimodal dispersion of Ag nanoparticles in the presence of IPA also enhances the electrical response of the Ag-PANIEB nanocomposite. A mechanism explaining the improvement in electrical response of bimodal Ag-PANIEB nanocomposite in the presence of IPA is proposed and discussed.

Polaron hopping mechanism of conducting polymer

To investigate the polaron hopping mechanism, thin films of polyaniline with solvent and without solvents were deposited over the surface of Al thin film and electrical properties were evaluated as a function of temperature ranging from - 60°C to 60°C. It was observed that all devices followed Arrhenius response of conductivity within given temperature range. The pre-exponential factor of conductivity and activation-energy for each device were found interrelated with isokinetic temperature (Meyer-Neldel Temperature) according to the Meyer-Neldel rule (MNR). It was examined that the solvent provides higher value of isokinetic temperature and lower value of activation energy, which may be due to the enhancement of solvent-induced crystallization, improvement of electronic energy transfer rate between molecular chains and softening of molecular vibration in polymer chains. The results demonstrate that IPA offers superior solvent response as compared to acetone for PANIEB matrix. The understandings obtained from this study will improve our knowledge for both the origin of MNR and the thermal-activated charge transport mechanism for conducting polymer in the presence of solvent.