Byoung Ryul Min

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.

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).

A new technique for preparation of PDMS pervaporation membrane for VOC removal

Abstract To improve the low flux and low selectivity in composite membranes for the removal of volatile organic components (VOC), a new composite membrane, which adopted polydimethylsiloxane (PDMS) as a top layer and non-woven fabric treated with polyethylene glycol (PEG) solution as a support layer, was developed. The preparation variables and the performance of the new membrane were investigated through a permeation test with toluene as a representative VOC. Intrusion thickness, which has a greater effect on membrane performance than the top layer thickness does, decreased when the concentration of PDMS and PEG increased, so that the permeation flux increased. The toluene flux of the new membrane with PEG-treated non-woven fabric showed a maximum increase of 37.4% over a composite membrane with polysulfone (PSf) and a 41.4% increase over that with non-woven fabric.

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.

Coordination structure of various ligands in crosslinked PVA to silver ions for facilitated olefin transport.

The most effective ligand among -OH, -O- and -CHO for facilitated olefin transport by silver ions in room temperature crosslinked poly(vinyl alcohol) membrane has been evaluated.

Synthesis of crosslinked polystyrene-b-poly(hydroxyethyl methacrylate)-b-poly(styrene sulfonic acid) triblock copolymer for electrolyte membranes

The synthesis and the characterization of crosslinked ABC triblock copolymer, i.e. polystyrene-b-poly (hydroxyethyl methacrylate)-b-poly(styrene sulfonic acid), (PS-b-PHEMA-b-PSSA) is reported. PS-b-PHEMA-b-PSSA triblock copolymer at 20:10:70 wt% was sequentially synthesized via atom transfer radical polymerization (ATRP). The middle block was crosslinked by sulfosuccinic acid (SA) via the esterification reaction between -OH of PHEMA and -COOH of SA, as demonstrated by FTIR spectroscopy. As increasing amounts of SA, ion exchange capacity (IEC) continuously increased from 2.13 to 2.82 meq/g but water uptake decreased from 181.8 to 82.7%, resulting from the competitive effect between crosslinked structure and the increasing concentration of sulfonic acid group. A maximum proton conductivity of crosslinked triblock copolymer membrane at room temperature reached up to 0.198 S/cm at 3.8 w% of SA, which was more than two-fold higher than that of Nafion 117(0.08 S/cm). Transmission electron microscopy (TEM) analysis clearly showed that the PS-b-PHEMA-b-PSSA triblock copolymer is microphase-separated with a nanometer range and well developed to provide the connectivity of ionic PSSA domains. The membranes exhibited the good thermal properties up to 250 °C presumably resulting from the microphase-separated and crosslinked structure of the membranes, as revealed by thermal gravimetric analysis (TGA).

Novel composite membranes comprising silver salts physically dispersed in poly(ethylene-co-propylene) for the separation of propylene/propane

Novel composite membranes, which delivered high separation performance for propylene/propane mixtures, were developed by coating inert poly(ethylene-co-propylene) rubber (EPR) onto a porous polyester substrate, followed by the physical distribution of AgBF4. Scanning electron microscopy-wavelength dispersive spectrometer (SEM-WDS) revealed that silver salts were uniformly distributed in the EPR layer. The physical dispersion of the silver salts in the inert polymer matrix, without specific interaction, was characterized by FT-IR and FT-Raman spectroscopy. The high separation performance was presumed to stem from thein-situ dissolution of crystalline silver ionic aggregates into free silver ions, which acted as an active propylene carrier within a propylene environment, leading to facilitated propylene transport through the membranes. The membranes were functional at all silver loading levels, exhibiting an unusually low threshold carrier concentration (less than 0.06 of silver weight fraction). The separation properties of these membranes, i.e. the mixed gas selectivity of propylene/propane ~55 and mixed gas permeance ~7 GPU, were stable for several days.

Characteristics of the lipase fromCandida rugosa modified with copolymers of polyoxyethylene derivative and maleic acid anhydride

The hydrophilic copolymer, polyethylene oxide (PEO) allyl ester-maleic anhydride (MA), copolymer was used to modify the lipase from Candida rugosa. MA, in a functional group, reacts easily with amino acids of lipase. The degree of modification (DM) was varied by changing the weight ratio of copolymer to protein of lipase over the range of 10–120 (w/w). The specific activity decreased as DM increased. At the maximum modification degree of 35%, the modified lipase retained more than 65% of the unmodified native lipase activity. The modified lipase displayed a high stability of activity against temperature and pH. The remaining activity of modified lipase was about 2–4 fold of that of native lipase in the severe pH and temperature condition. Finally, it showed 20% greater reaction of substrate at 10 hr than in the case where native lipase was used.

The energy of an ion in a cylindrical pore of a low dielectric membrane

Abstract Based on electrodynamic theory, the equation of the potential energy is derived from the potential energy of an ion in a cylindrical pore. Consequently the infinite rejection coefficient (R∞) of the membrane increase from the reduction of the ratio of ∈ hc /∈ p . Also if both spherical and cylindrical pores have the same energy differences and partition coefficients, the ratio of the pore radius to the sphere radius is found to be R p / .

FT-Raman Studies on Ionic Interactions in π-Complexes of Poly(hexamethylenevinylene) with Silver Salts

Remarkably high and stable separation performance for olefin/paraffin mixtures was previously reported by facilitated olefin transport through π-complex membranes consisting of silver ions dissolved in poly(hexamethylenevinylene) (PHMV). In this study, the π-complex formation of AgBF4, AgClO4 and AgCF3SO3 with PHMV and their ionic interactions were investigated. FT-Raman spectroscopy showed that the C=C stretching bands of PHMV shifted to a lower frequency upon incorporation of silver salt, but the degree of peak shift depended on the counteranions of salt due to different complexation strengths. The symmetric stretching modes of anions indicated the presence of only free ions up to [C=C]∶[Ag]=1∶1, demonstrating the unusually high solubility of silver salt in PHMV. Above the solubility limit, the ion pairs and higher-order ionic aggregates started to form. The coordination number of silver ion for C=C of PHMV was in the order AgBF4>AgClO4>AgCF3SO3, but became similar at [C=C]∶[Ag]=1∶1. The different coordination number was interpreted in terms of the different transient crosslinks of silver cations in the complex, which may be related to both the interaction strength of the polymer/silver ion and the bulkiness of the counteranion.