Yong Soo Kang

Zeolite-filled polyimide membrane containing 2,4,6-triaminopyrimidine

Abstract Interfacial void-free Matrimid polyimide (PI) membranes filled with zeolites were prepared by introducing 2,4,6-triaminopyrimidine (TAP). TAP enhanced the contact of zeolite particles with polyimide chains presumably by forming hydrogen bonding between them. The threshold amount of TAP, needed to depress totally the void formation, varied with zeolite type in the order of zeolite 4A≈13X

Membrane formation by water vapor induced phase inversion

The membrane formation by the phase inversion process was studied by coagulating a polysulfone/N-methyl-2-pyrrolidone solution with water vapor as a coagulant. The phase separation occurred when the relative humidity in the membrane casting atmosphere was higher than about 65%. The pore size was strongly affected by the relative humidity as well as the concentration of the polymer solution. It increased as both the relative humidity and the polymer concentration were decreased. The membranes produced showed a uniform structure composed of closed pores. The pure water flux measurement confirmed the closeness of the pores. The information on the late stage phase separation was obtained in situ by an optical microscope due to the slow phase separation. The pores seemed to grow very much at the late stage by coarsening which was observed to occur mainly by coalescence of polymer-lean droplets. As the relative humidity was lower, the coarsening continues longer ending up to a larger droplet size. The coarsening seems to enhance the interconnectivity of pores when the polymer concentration was low enough.

Structural characterization and surface modification of sulfonated polystyrene–(ethylene–butylene)–styrene triblock proton exchange membranes

Structural characteristics and membrane performance of polystyrene-block-poly(ethylene-ran-butylene)-block-polystyrene (sSEBS) copolymer proton exchange membranes in water-swollen and different ratio of water/methanol-swollen are studied by small angle X-ray scattering (SAXS), ATR FT-IR, AFM. SAXS profile of sSEBS membrane showed that microstructure was a hexagonally cylindrical structure and it was maintained in the existence of methanol in water until 30 wt.%. As the main interest was on the development of proton exchange membranes for fuel cells operating at lower temperature with liquid methanol feed, a selective thin layer was introduced on the top of sSEBS membrane by simple plasma treatment in the presence of maleic anhydride in order to prevent methanol crossover. Both methanol permeability and proton conductivity gradually decreased with increasing loading amounts of maleic anhydride. Hydrophobic anhydride properties on the top of sSEBS membrane act as a barrier for methanol but also for proton, resulting in decreasing methanol permeability and proton conductivity. The hydrolysis of anhydride groups to carboxylic acid provides a facilitated transport site for the proton. After hydrolysis, the proton conductivity was recovered and the recovery rate of proton conductivity by hydrolysis was higher than that of methanol permeability.

Phase behavior and mechanism of membrane formation for polyimide/DMSO/water system

Abstract A macrovoid-free, sponge-like porous membrane was prepared from polyimide/DMSO/water system, whereas a finger-like membrane was obtained from a polyimide/NMP/water system by phase inversion. The sponge-like membrane structure was investigated by the thermodynamics and kinetics of the phase separation process. The rates of phase separation for both systems were similar, but their phase diagrams were significantly different. The distinct features of the phase diagram for the polyimide/DMSO/water system are: (1) extremely narrow miscibility gap, (2) close gelation point to the binodal curve, and (3) almost parallel tie-line passing through the gelation point to the polymer–solvent axis. These properties hinder the phase separation process to proceed further, i.e. the growth of the polymer-lean phase is, thus frozen or stopped in the early stages. Therefore, the membrane morphology will be determined at an earlier stage in the polyimide/DMSO/water system than polyimide/NMP/water, resulting in a macrovoid-free, sponge-like membrane.

Dye-sensitized nanocrystalline solar cells based on composite polymer electrolytes containing fumed silica nanoparticles

We report remarkably high energy conversion efficiency (4.5% at 100 mW cm(-2)) of a dye-sensitized solar cell in the solid state, using composite polymer electrolytes containing fumed silica nanoparticles.

Facilitated transport of ethylene across polymer membranes containing silver salt: effect of HBF4 on the photoreduction of silver ions

Abstract Silver salts dissolved in amide group containing polymer such as poly(2-ethyl-2-oxazoline) (POZ) are labile to reduce to silver metals under UV-Vis light or heat. Since the reduction of silver ions to silver nanoparticles can change the separation performance of facilitated olefin transport through polymer membranes containing silver salt, it is attempted to prohibit the reduction of silver ion. It is found that the trace of water present in silver–polymer complex membranes participates in the reduction reaction and H + ions are generated in a reversible reaction of the reduction process. In this respect, tetrafluoroboric acid (HBF 4 ) was introduced as a proton donator to suppress the reduction of silver ion. The effects of HBF 4 on the photoreduction derived by UV irradiation were characterized by mixed gas transport of ethylene/ethane, UV-Vis spectroscopy, scanning electron microscopy (SEM).

Complexation mechanism of olefin with silver ions dissolved in a polymer matrix and its effect on facilitated olefin transport.

Remarkable separation performance of olefin/paraffin mixtures was previously reported by facilitated olefin transport through silver-based polymer electrolyte membranes. The mechanism of facilitated olefin transport in solid membranes of AgCF3SO3 dissolved in poly(N-vinyl pyrrolidone) (PVP) is investigated. In silver polymer electrolyte membranes, only free anions are present up to the 2:1 mole ratio of [C=O]:[Ag], and ion pairs start to form at a ratio of 1:1, followed by higher-order ionic aggregates above a ratio of 1:2. At silver concentrations above 3:1, the propylene permeance increases almost linearly with the total silver concentration, unexpectedly, regardless of the silver ionic constituents. It was also found that all the silver constituents, including ion pairs and higher order ionic aggregates, were completely redissolved into free anions under the propylene environment; this suggests that propylene can be a good ligand for the silver cation. From these experimental findings, a new mechanism for the complexation reaction between propylenes and silver salts in silver-polymer electrolytes was proposed. The new mechanism is consistent with the linearity between the propylene permeance and the total silver concentration regardless of the kind of the silver constituents. Therefore, the facilitated propylene transport through silver-polymer electrolytes may be associated mainly with the silver cation weakly coordinated with both carbonyl oxygen atoms and propylene.

Facilitated olefin transport by reversible olefin coordination to silver ions in a dry cellulose acetate membrane.

The highly selective dry complex membrane AgBF4-cellulose acetate (CA) was prepared and tested for the separation of ethylene/ethane and propylene/propane mixtures. The maximum selectivity for olefin over paraffin was found to be 280 for the ethylene/ethane mixture and 200 for the propylene/propane mixture. Solid-state interactions of AgBF4 with cellulose acetate (CA) and/or olefins have been investigated by using FT-IR, UV, and X-ray photoelectron spectroscopy (XPS). FT-IR and XPS studies clearly show that the silver ions are coordinated by carbonyl oxygen atoms among three different types of oxygen atoms present in CA-two in the acetate group and one in the ether linkage. Upon incorporation of AgBF4 into CA, the carbonyl stretching frequency of the free cellulose acetate at 1750 cm(-1) shifts to a lower frequency by about 41 cm(-1). The binding energy corresponding to a carbonyl oxygen atom in the O 1s XPS spectrum shifts to a more positive binding energy by the incorporation of AgBF4. Reversible olefin coordination to silver ions has been observed by FT-IR and UV studies. Treatment of the AgBF4-CA membrane placed in a gas cell with propylene produces a propylene-coordinated membrane in which coordinated propylene is easily replaced by other olefins such as 1,3-butadiene.

Facilitated transport of olefin through solid PAAm and PAAm-graft composite membranes with silver ions

Abstract Solid poly(acrylamide) (PAAm) composite membranes containing silver ions have been investigated for olefin/paraffin separation. The propylene permeance increased significantly for a solid PAAm/AgBF 4 composite membrane with increasing loading amount of silver ions. Silver ions in solid PAAm form reversible complexes with propylene, resulting in the facilitated transport of propylene. The propylene selectivity of 100 over propane was obtained when the mole ratio of silver ions to acrylamide unit was 1. This high separation performance would be obtained predominantly because of the high loading of the propylene carrier, silver ions. PAAm-graft/AgBF 4 composite membranes were prepared in order to improve the gas permeance. Introduction of PAAm grafts on a polysulfone microporous membrane surface was confirmed by FT-IR spectroscopy. The propylene permeance was increased through the PAAm-graft/AgBF 4 membranes compared to that through of the PAAm/AgBF 4 composite membranes, indicating the formation of ultra-thin top layer.

Surface modification of polyimide and polysulfone membranes by ion beam for gas separation

The surface carbonization of polyimide (PI) and polysulfone (PSf) by ion beam has been performed to adapt the carbon molecular sieve properties on the skin of the polymeric membranes without the deformation of the membrane structure. In order to control the structure of membrane skin and to improve gas transport properties, the irradiation conditions, such as the dosage and the source of ion beams, have been varied. The ideal separation factor of CO2 over N2 through the surface-modified PI and PSf membranes increased threefold compared to those of the untreated, pristine membranes, whereas the permeability decreased with almost two orders of magnitude. This appears to be due to the fact that the structure of membrane skin has been changed to a barrier layer. The formation of barrier layer was confirmed by comparing the calculated values of a simple resistance model with the experimental results, and the estimated permeability of this barrier was 10−4 barrer. It was concluded that ion beam irradiation could provide a useful tool for improving selectivity for gas separation membranes.