Un Young Kim

Plasma protein adsorption to sulfonated poly(ethylene oxide)‐grafted polyurethane surface

Adsorption of proteins (fibrinogen, albumin, and gamma globulin) from plasma onto surface-modified PUs (PU-PEO, PU-SO3, and PU-PEO-SO3) was evaluated. Adsorbed fibrinogen at steady state decreased in the order PU-SO3 > PU > PU-PEO-SO3 > PU-PEO, suggesting that sulfonate groups have specific high affinity to fibrinogen. The intermediate fibrinogen adsorption on PU-PEO-SO3 can be explained by the compensatory effect between the low protein binding affinity of the PEO chain and the high fibrinogen binding affinity of the sulfonate group. In addition, PU-PEO-SO3 showed a very fast fibrinogen adsorption due to the high accessibility of the sulfonate group to fibrinogen by the poly(ethylene oxide) (PEO) spacer. The kinetic profiles of their surfaces showed that as the adsorption time increases, fibrinogen initially adsorbed was decreased and a plateau reached, demonstrating that all the surfaces exhibited the Vroman effect (the fibrinogen displacement phenomenon). PU-PEO showed the least fibrinogen and albumin adsorption among PUs, confirming the known nonadhesive property of PEO chains. It is very interesting that PU-PEO-SO3 exhibited the highest adsorption of albumin and the lowest adsorption of IgG. Therefore, it may be concluded that such adsorption behaviors of proteins to PU-PEO-SO3 contribute to improved blood compatibility.

Operation parameters of melt spinning of polypropylene hollow fiber membranes

Microporous hollow fiber membranes were prepared via melt spinning of a polypropylene/soybean oil mixture. Many operation parameters of melt spinning process were examined in terms of the structure variation by scanning electron microscopy and bubble point pressure measurement. The initial composition of the melt solution affected the porosity and the pore size of the membrane. Melt viscosity of the hollow fiber spun depended on the spinning temperature and affected the structure. Increased melt-draw ratio enhanced the formation of the micropores and fibril structure. Subsequent cold-stretching of the hollow fiber membrane produced tiny fibrils and micropores via stretching and cleavage. A combination of thermally-induced phase separation and cold-stretching produced an unusually highly porous membrane without significant changes of the inside and outside diameters of the hollow fiber membranes.

Structural study of microporous polypropylene hollow fiber membranes made by the melt-spinning and cold-stretching method

Abstract Microporous polypropylene hollow fiber membranes were prepared by the melt-spinning and cold-stretching method. Factors affecting the membrane structure were melt-draw ratio, spinning temperature, and annealing temperature. The degree of molecular orientation was affected by the melt-draw ratio and spinning temperature, and the crystallinity of the hollow fiber depended on the melt-draw ratio and annealing temperature. Quantitative analyses of microporous membrane structure were performed by image analysis, bubble point pressure measurement, and mercury porosimetry. The porosity at the surface is smaller than that of the whole membrane. Wetting of the medium and shading in the image brought about the differences in pore size determination by each method.

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.

Analysis of facilitated transport in polymeric membrane with fixed site carrier 2. Series RC circuit model

Abstract A new mathematical model for facilitated mass transport in a polymeric membrane with a fixed-site carrier was developed by extending the single RC circuit model, which was derived by assuming concentration fluctuation and analogy between electron transport in a parallel resistor-capacitor (RC) circuit and mass transport in a facilitated transport membrane. Here, a series of parallel RC circuits was employed instead of the single RC circuit to take account of the four diffusion pathways, demonstrating solute transfer between matrix and carrier. It was then examined against the experimental data on oxygen transport through poly(dimethyl siloxane), poly(butyl methacrylate) and poly(methyl methacrylate) with a metallo-porphyrin carrier. The current model showed a better agreement than the single circuit model but the difference was minor.

Morphology control of asymmetric membranes by UV irradiation on polyimide dope solution

Abstract The membrane morphology was readily controlled by the gelation of dope solution before immersion into a coagulation medium. In particular, macrovoid-free, sponge-like integrally skinned asymmetric polyimide membranes with improved selectivity were obtained by the chemical gelation of cast solution film. Cross-linking was performed by ultraviolet irradiation for benzophenone containing polyimide dope solution. Cross-linking maintained the structure of cast solution film until the moment of immersion into a nonsolvent bath. Macrovoid decreases with irradiation time on the cast solution film. Sponge-like integrally skinned asymmetric membranes were obtained with sufficient irradiation. Gas permselectivity increased significantly with the progress of cross-linking on the cast solution film. Membrane morphology and subsequent transport properties can be controlled both by the extent of cross-linking and by the concentration of dope solution.

Light scattering and membrane formation studies on polysulfone solutions in NMP and in mixed solvents of NMP and ethyl acetate

The relationship between the characteristics of the polymer dope solution and the skin formation mechanism as well as the performance of the asymmetric membrane has been investigated. The solution characteristics have been studied on the polysulfone (PSf) dope solution as a function of the concentrations of both polymer and the cosolvent, ethyl acetate (EA), by dynamic light scattering. An anomalous light scattering was observed at small angles in both PSf/NMP and PSf/NMP:EA (6:4 by weight) solutions, indicating the inhomogeneity of the dope solutions. In the case of the PSf/NMP:EA (6:4) solution, an integrally skinned asymmetric membrane without defects having high gas selectivity was obtained while the membrane from the PSf/NMP solution had a defective skin. The scattered light intensity of the dope solution of PSf/NMP:EA (6:4) increased with the aging time while no notable change was observed in the PSf/NMP solution. The characteristics of the solution affect the final morphology of the membrane, particularly when phase separation occurred significantly before the immersion into the gelation medium.

The effect of dope solution characteristics on the membrane morphology and gas transport properties : PES/γ-BL/NMP system

The effect of heterogeneity of a dope polymer solution on membrane morphology has been investigated. Heterogeneity was developed in polyethersulfone solutions of either γ-butyrolactone (γ-BL) or a mixed solvent of γ-BL/N-methyl-2-pyrrolidone, which exhibit gelation and/or phase separation with aging time. Two different processes for membrane preparation have been employed; Process I, heterogeneity-developed dope solution was cast on a glass plate with a knife for uniform thickness, and immediately immersed into a nonsolvent form of the membrane. Process II, a dope solution was cast on a glass plate and then aged in a closed environment. After a certain aging time, it was immersed into a nonsolvent to be coagulated. The developed heterogeneity was destroyed markedly during casting in Process I, whereas the heterogeneity was maintained until the moment of immersion into a coagulation medium in Process II. Membranes prepared by Process I were finger-like regardless of the aging time, whereas Process II yielded macrovoid-free and sponge-like membranes having enhanced gas permeance and mechanical strength at long aging times. From these results, it was concluded that the morphology and transport properties of a membrane were able to be controlled by the solution structure, in particular, the solution heterogeneity in the cast film.

Pervaporation of Water/Ethanol Mixture Through Hydrophilically Modified Polyimide Membrane

Abstract Polyimide of pyromellitic dianhydride (PMDA) and 4,4′-oxydianiline (ODA) was hydrophilically modified by partial replacing of ODA with 3,5-diaminobenzoic acid (DABA) containing a carboxylic group with two amine groups. Pervaporation experiments of water/ethanol mixture were performed and the results demonstrated that both flux and permselectivity increase simultaneously with increasing DABA content in polyimide backbone. From the sorption and temperature-dependent permeation behavior, it could be concluded that the diffusivity of permeant plays a major role in determining the pervaporation performance rather than the solubility.