Taek Sung Hwang

In Situ Microfluidic Synthesis of Monodisperse PEG Microspheres

This study presents a microfluidic method for the production of monodisperse poly(ethylene glycol) (PEG) microspheres using continuous droplet formation and in situ photopolymerization in microfluidic devices. We investigated the flow patterns for the stable formation of droplets using capillary number and the flow rate of the hexadecane phase. Under the stable region, the resulting microspheres showed narrow size distribution having a coefficient of variation (CV) of below 1.8%. The size of microspheres (45∼95 ώm) could be easily controlled by changing the interfacial tension between the two immiscible phases and the flow rates of the dispersed or continuous phase.

The synthesis of poly(vinylphosphonic acid-co-methacrylic acid) microbeads by suspension polymerization and the characterization of their indium adsorption properties.

Poly(vinylphosphonic acid-co-methacrylic acid) microbeads were synthesized by suspension polymerization, and their indium adsorption properties were investigated. The obtained microbeads were characterized by Fourier transform infrared (FT-IR) spectroscopy and scanning electron microscopy (SEM). The microbeads were wrinkled spheres, irrespective of the components, and their sizes ranged from 100 to 200 μm. The microbeads were thermally stable up to 260°C. As the vinylphosphonic acid (VPA) content was increased, the synthetic yields and ion-exchange capacities decreased and the water uptakes increased. The optimum synthetic yield, ion-exchange capacity and water uptake were obtained at a 0.5 mol ratio of VPA. In addition, the maximum adsorption predicted by the Langmuir adsorption isotherm model was greatest at a 0.5 mol ratio of VPA.

Synthesis and Characterization of EFFE-g-(VBTAC-co-HEMA) Anion Exchange Membranes Prepared by a 60Co Radiation-Induced Graft Copolymerization for Redox-Flow Battery Applications

AbstractVinyl benzyl trimethyl ammonium chloride (VBTAC) was grafted onto poly(ethylene-co-tetrafluoroethylene) (ETFE) film by γ-ray using simultaneous irradiation graft copolymerization in the presence of 2-hydroxyl ethyl methacrylate (HEMA). The structure of the ETFE-g-(VBTAC-co-HEMA) anion membrane was confirmed by Fourier transform infrared spectroscopy and thermogravimetric analysis. The degree of grafting (DG) of the membrane increased with total irradiation dose and VBTAC monomer concentration. The highest DG of an ETFE-g-(VBTAC-co-HEMA) membrane was 92%, which was synthesized by the treating of an ETFE film with a 0.8 M solution of VBTAC monomer in the presence of 50 kGy irradiation. Different properties of the anion membrane, such as water uptake and ion exchange capacity, increased as DG increased. The permeability and vanadium redox-flow battery performance were measured for a membrane with a DG of 92%. The average voltage efficiency, coulombic efficiency, and energy efficiency were 0.79, 0.88, and 0.70, respectively, all of which remained stable as the number of cycles increased.

Characterization for Pyrolysis of Thermoplastic Polyurethane by Thermal Analyses

The pyrolysis kinetics of polyurethanes synthesized from polycaprolactone diol (PCL) and diisocyanate (HDI, H12MDI) using catalysts such as dibutyltin dilaurate (DBTDL) were studied by a thermogravimetric (TG) technique, which involved heating the sample at the rates of 10, 20 and 30 °C/min. The effect of the kind of diisocyanate and the hard segment contents on the activation energy and reaction order were examined at conversions ranging from 1 to 100%. The activation energies at first increased slowly with increasing conversion. Also, differential scanning calorimetry (DSC) was used to investigate the structural differences in each polyurethane. DSC can reveal the melting behavior, in terms of the glass transition temperature (Tg), which is known to vary as a function of the stoichiometry and processing conditions.

Preparation of Modified Hollow Polypropylene Membrane and Their Adsorption Properties of γ-Globulins

The hydrophobic ligand-containing hollow polypropylene (PP) membranes were synthesized by the mutual radiation induced graft copolymerization with glycidylmethacrylate (GMA) onto hollow PP membrane followed by the subsequent functionalization with L-phenylalanine. FT-IR, elemental analysis and UV spectroscopy were utilized to characterize copolymer composition, and degree of grafting, functionalization conversion and γ-globulins adsorption. The degree of grafting on the PP surface increased with the reaction time and total dose of E-beam. In the subsquent functionalization, the amount of L-phenylalanine increased with the increase in the degree of grafting and the degree of conversion was about 30%. The γ-globulins adsorption experiments showed that adsorption capacity had a maximum value at pH 8. The γ-globulins adsorption capacity in the basic pH region was higher than in the acidic pH region.

UV-Induced Graft Polymerization of Polypropylene-g-glycidyl methacrylate Membrane in the Vapor Phase

UV-induced graft polymerization of glycidyl methacrylate (GMA) to a polypropylene (PP) membrane was carried out in the vapor phase with benzophenone (BP) as a photoinitiator. Attenuated total reflection Fourier transform infrared spectroscopy, atomic force microscopy (AFM), and scanning electron microscopy (SEM) were utilized to characterize the copolymer. The degree of grafting increased with increasing reaction time, increased UV irradiation source intensity, and increased immersion concentration of the BP solution. The optimum synthetic condition for the PP-g-GMA membrane was obtained with a reaction time of 2 hrs, a UV irradiation source intensity of 450W, and an immersion concentration of the BP solution of 0.5 mol/L. The pure water flux decreased upon increasing the degree of grafting and increasing the amount of diethylamino functional group introduced. The analysis of AFM and SEM images shows that the graft chains and diethylamino groups of PP-g-GMA grew on the PP membrane surface, resulting in a change in surface morphology.

Synthesis and characteristics of UV curable dimethyl 5-sulfoisophthalate sodium salt-co-diethylene glycol with maleic and phthalic anhydride copolymers (DMSIP-co-DEG-co-MA/PA) for application in redox flow batteries

AbstractDimethyl 5-sulfoisophthalate sodium salt (DMSIP)-co-diethylene glycol (DEG)-co-maleic anhydride (MA)/phthalic anhydride (PA) oligomers were synthesized via condensation reaction and the corresponding membranes were prepared by UV curing. The number-average molecular weight (Mn) of the DMSIP-co-DEG-co-MA/PA (DDMP) was proportional to the concentration of DMSIP and ranged from 1,360–2,856 g/mol. A successful introduction of a -SO3Na group to the main oligomer chain was confirmed using Fourier transform infrared (FTIR) and nuclear magnetic resonance (NMR) spectroscopy and the thermal stability of the membranes up to 300 °C was analyzed using thermogravimetric analysis (TGA). The water uptake values, swelling ratios, and the ion-exchange capacities of the membranes were 13%–30%, 7%–15%, and 0.7–0.9 meq/g, respectively. The electrical properties of the membrane, including the area resistance, ion transport number, and the cyclic charge-discharge current were also analyzed; these properties confirmed that these membranes were suitable for use in redox flow battery (RFB) applications.

Synthesis of polyketone-g-vinylbenzyl chloride anion exchange membrane via irradiation and its properties

AbstractA novel anion exchange membrane composed of aminated polyketone-g-vinylbenzyl chloride was synthesized via60Co γ-ray irradiation grafting technique. Total irradiation dose and concentration of monomers were set as variables to determine degree of grafting. Fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy equipped with energy dispersive X-ray spectrometer (SEM-EDS) were used to characterize the grafted membranes. Water uptake (WU) and swelling ratio (SR) were measured with a gravimetric method. A titration method was used to detect ion exchange capacity (IEC), whereas electrical resistance (ER) and ion conductivity (IC) were measured with a LCR meter. Our method has boosted the degree of grafting up to 97.6% from 3.7% as total irradiation dose and monomer concentration have been increased. WU and SR were in the ranges 1.5%-35.6% and 0.35%-20.9%, respectively. Also, IEC has taken values ranging between 0.2 and 1.19 meq/g. IC has varied within the range 0.01-0.3 S cm-1, and it has shown a rising trend as IEC increased. In this study, the optimum synthesis conditions have been 70 kGy of total irradiation dose and 50wt% of monomers. The membrane synthesized here is potentially superior to Nafion membrane in terms of several properties.

Synthesis and properties of sodium vinylbenzene sulfonate-grafted poly(vinylidene fluoride) cation exchange membranes for membrane capacitive deionization process

In this study, a poly(vinylidene fluoride)-graft-sodium 4-vinylbenzene sulfonate copolymer (PVDF-g-PSVBS) was prepared by grafting sodium 4-vinylbenzene sulfonate (SVBS) onto dehydrofluorinated poly(vinylidene fluoride) (PVDF). The PVDF-g-PSVBS cation exchange membranes were prepared using a casting method. The structure of the membranes was investigated with Fourier transform infrared spectroscopy (FTIR) and Raman spectroscopy. Morphology using scanning electron microscope with energy-dispersive X-ray analysis (SEM-EDS) demonstrated as increasing the degree of grafting, the sulfur element is uniformly distributed and increased. The effects annealing temperature on the properties of the PVDF-g-PSVBS membranes were investigated. To prepare the consistent and homogeneous membranes, it was suggested that the annealing temperature of PVDF-g-PSVBS membranes is below 60 °C. The salt removal efficiency for application to the membrane capacitive deionization (MCDI) process was conducted.

Photocurable Polyimide Gate Insulator for Pentacene Thin-Film Transistor With Excellent Chemical Resistance by Low Temperature Processing

We introduce a photo-curable polyimide-based gate insulator for organic thin-film transistors (OTFTs) that allows low-temperature and solution-based processing and provide low leakage current density and high field-effect mobility in devices. Organic gate insulator (PI-TTE) was prepared from a blend of 75.2 wt% hydroxyl group containing polyimide (PI) and 23.8 wt% trimethylolpropane triglycidyl ether as the crosslinker, 0.5 wt% benzoyl peroxide, and 0.5 wt% triphenylsulfonium triflate as the photoacid generator (PAG). PI-TTE showed extremely low leakage current density as 2.33 × 10−10 A/cm2 at 3.3 MV/cm and exhibited a very stable capacitance (96.74 pF/mm2) and it is unchangeable up to 600 hrs. Pentacene TFT using PI-TTE as a gate dielectric showed a field effect mobility as 0.203 cm2/Vs and an on/off ratio of 1.55 × 105 with almost no hysteresis.