Young Chan Bae

Comparison of Ag deposition effects on the photocatalytic activity of nanoparticulate TiO2 under visible and UV light irradiation

We investigated the photocatalytic degradation of rhodamine B (RB) dye in the aqueous suspensions of TiO2 (∼17 nm) and Ag-deposited TiO2 nanoparticles under visible and UV light irradiation in order to evaluate and distinguish various effects of the Ag deposition on the TiO2 photocatalytic activity. The TiO2 and Ag–TiO2 photocatalysts were characterized by XRD, TEM, XPS, UV-visible absorption and photon correlation spectroscopy. For comparison, the RB photodegradation was carried out in Degussa P25 TiO2 and Ag-deposited P25 suspensions under the same condition. In the RB/Ag–TiO2 system, Ag deposits significantly enhanced the RB photodegradation under visible light irradiation whereas the RB photodegradation under UV irradiation was slightly enhanced. The significant enhancement in the Ag–TiO2 photoactivity under visible light irradiation can be ascribed to simultaneous effects of Ag deposits by both acting as electron traps and enhancing the RB adsorption on the Ag–TiO2 surface.

Liquid-liquid equilibria for binary polymer solutions from modified double-lattice model

A new double-lattice model, which is capable of describing and predicting the equilibrium properties of binary polymer solutions, was proposed by modifying Hus double-lattice model by introducing a new interaction parameter and simplifying the expression of the Helmholtz energy of mixing. Using the proposed model, we investigated phase behaviours of various binary polymer solutions. The modified double-lattice model successfully describes the phase behaviours of binary polymer solutions having an upper critical solution temperature (UCST) and a lower critical solution temperature (LCST).

Polymeric separation media for electrophoresis: Cross-linked systems or entangled solutions

Abstract The current status of separation media development for capillary electrophoresis is reviewed in fight of well-known electrophoretic migration and entangled polymer solution theories. The relative strengths and weaknesses of crosslinked systems and entangled solutions are also examined. The residence time limit of DNA in a mesh is estimated and compared with the relaxation time of both a typical entangled polymer solution and a cross-linked gel. By advancing the concept of analyte residence time and life time of a characteristic network mesh, we can highlight the differences between the operative mechanism governing separation in these two types of electrophoresis media.

The Effect of Morphological Properties on the Electrochemical Behavior of High Tap Density C – LiFePO4 Prepared via Coprecipitation

High-tap-density olivine C-LiFePO 4 , which is used as a positive electrode material in lithium-ion secondary batteries, was prepared via coprecipitation. The C-LiFePO 4 powders were prepared at various calcination temperatures between 650 and 850°C. The structural, electrochemical, and morphological properties, as well as the thermal stability of the prepared powders, were characterized by X-ray diffraction, scanning electron microscopy (SEM), transmission electron microscopy, and elemental analysis. Highly crystalline C-LiFePO 4 with a Pnma space group and a high tap density of 1.09 g cm -3 was obtained. Elemental analysis showed that the final product contained about 3 wt % carbon as a result of the carbon-coating process. SEM showed that the prepared materials consisted of secondary agglomerates with a 1-2 μm particle size, while the particle size of the primary particles was less than 100 nm. The C-LiFePΟ 4 materials prepared at 800°C exhibited an excellent rate capability of 150.8 mAh g -1 at the 0.1 C discharge rate and 106.7 mAh g -1 at the 10 C discharge rate.

Phase behaviors of hyperbranched polymer solutions

Abstract We developed a new model based on the lattice cluster theory to describe phase behaviors of binary hyperbranched polymer solution systems. To account for highly oriented interactions between segments, the proposed model requires an additional parameter ( δe / k ) related to the energy of the oriented interaction. A thermo-optical analysis (TOA) technique was used to determine cloud-points for the given systems. Hyperbranched polyol/water systems exhibit an upper critical solution temperature (UCST) behavior.

Phase transition of submicron sized N-alkylacrylamide-derivative copolymer particles: applicability of photon correlation spectroscopy

Abstract N -isopropylacrylamide (NIPA)/ N - tert -butylacrylamide (NTBA) and NIPA/ N,N -dimethylacrylamide (NDMA) submicron-sized copolymer gel particles of various compositions were prepared by precipitation polymerization and their swelling behaviours were studied with different compositions and temperature using photon correlation spectroscopy. The experimental data showed that the volume transition temperature ( T v ) of NIPA/NTBA copolymer gel decreased with increasing mole ratio of NTBA, while T v of NIPA/NDMA copolymer gel increased with the mole ratio of NDMA.

Viscosity reduction of polymeric liquid by dissolved carbon dioxide

The viscosities of polydimethylsiloxane (PDMS)/CO2 solutions were measured over the range of pressures of 1–3 MPa and at the ambient temperature. The viscosities were measured by using a specially designed falling ball viscometer (FBV). The Stokes equation was used to determine the viscosities and the Stokes force expressing the viscous drag of the sphere was corrected for the effect of the lateral cylindrical wall. The Kelley-Bueche (KB) free-volume treatment of the viscosities of polymeric solutions was modified to account for the gas solvent and applied to interpret our data on PDMS/CO2 systems. It was shown that the theoretical equation, based on the assumption of the additivity of free volumes of the components, was capable of predicting with remarkable accuracy the concentration and pressure dependence of the viscosities of the investigated polymeric solutions.

Effects of Metal Ions on the Structural and Thermal Stabilities of Li [ Ni1 − x − y Co x Mn y ] O2 ( x + y ⩽ 0.5 ) Studied by In Situ High Temperature XRD

Highly crystalline Li[Ni 1-x-y Co x Mn y ]O 2 (x + y ≤ 0.5) (Li[Ni 0.6 Co 0.2 Mn 0.2 ]O 2 , Li[Ni 0.55 Co 0.15 Mn 0.3 ]O 2 , and Li[Ni 0.5 Co 0.25 Mn 0.25 ]O 2 ) were synthesized through a coprecipitation method. The capacities of the prepared samples were proportional to the amount of Ni in the host structure. The thermogravimetric analysis (TGA) and in situ high-temperature-X-ray diffraction (HT-XRD) analysis revealed that changes in the amount of manganese ions in the host structure profoundly affect the structural stability of the samples with x + y ≤ 0.5. Li[Ni 0.55 CoO 0.15 Mn 0.3 ]O 2 , containing the highest manganese content (y = 0.3), showed the most stable structural integrity among the samples as confirmed by in situ HT-XRD. The electrochemical performances of the samples in Ni amount (0.5 ≤ 1 - x - y ≤ 0.6) with the variation of Co (0.15 ≤ x ≤ 0.25) did not significantly vary under the test conditions (3.0-4.3 V). The small increase of Mn ions plays an important role in preservation of its initial structural symmetry during the high-temperature heating as well as electrochemical cycling. Furthermore, the structural stability has a relationship with the thermal stability and the electrochemical stability, especially at an elevated temperature (55°C). On the basis of the differential scanning calorimetry and TGA results, the Li[Ni 0.55 Co 0.15 Mn 0.3 ]O 2 sample demonstrated improved thermal stability compared to the other samples.

Liquid–liquid equilibria of polydisperse polymer systems: applicability of continuous thermodynamics

Abstract Continuous thermodynamics is a suitable tool for describing the thermodynamic properties of solutions of polydisperse polymers. To represent liquid–liquid equilibria of polydisperse polymer/solvent systems, a continuous distribution function to represent the composition of polydisperse polymers has to be considered. In this study, we calculate the molar mass distributions of both principal phases and conjugate phases, using the extended Flory–Huggins model. The results for various polydisperse polymer systems are compared with experimental data.

Swelling behavior of submicron gel particles

We prepared submicron Poly(N-isopropylacrylamide) gel particles. Their swelling behavior was investigated by a photon correlation spectroscopy (PCS) technique. The swelling behavior of submicron gel particles showed a continuous volume phase transition for various temperatures. We combined the extended Flory-Huggins model for mixing solvent and network with a modified Flory-Rehner theory for the elastic contribution. The proposed model agreed very well with swelling behaviors of both submicron gel particles and bulk gels. A continuous volume phase transition behavior of submicron gel particles was predicted successfully by the proposed model.