The control of 3-dimensions membrane structure is of primary concern in the development of new separation membranes. Here, a new possibility for separation membrane is presented using a phase inversion process. The structure of the asymmetric membrane fabricated by a dry/wet phase inversion process showed an ultrathin skin layer and sponge-like structure characterized by the presence of macrovoids. We have prepared a series of asymmetric membranes with different defect-free skin layer thicknesses from 10 to 5.0×10³nm by the dry/wet phase inversion.The gas selectivity of the asymmetric membrane increases with a decrease in the surface skin layer thickness, which may be due to the fact that the surface skin layer of the membrane with a thinner thickness forms a more packed structure. On the other hand, porous membranes with nanoscale pore sizes are of interest in areas such as catalysis, sensors, size-and shape-selective separation media, adsorbents, and scaffolds for composite materials synthesis.Those with pore sizes on the order of 1nm to 10μm are required. A new possibility for porous membrane is presented using a phase inversion process.

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The thermally induced phase separation (TIPS) process is a valuable way of making microporous materials, such as membranes and foams. TIPS process consists of the following steps.
1. A homogeneous solution is formed at an elevated temperature by blending the polymer with a high-boiling, low molecular weight liquid (diluent).
2. The solution is formed into the desired shape (flat sheet, tube, hollow fiber).
3. The solution is cooled at a controlled rate or quenched to induce phase separation.
4. The diluent is removed typically by solvent extraction.
5. The extracatnt is removed typically by evaporation to produce a microporous structure.
This paper mainly focuses on the kinetics of phase separation in the TIPS process. The studies on phase separation by the light scattering method, kinetics of droplet growth in the latter stage of phase separation and the computer simulation on dynamics of spinodal decomposition are reviewed briefly. Accurate engineering of the TIPS process is essential for control of microstructural properties such as pore size, pore size distribution and porosity, since these properties ultimately determine the performance of the microporous membranes.

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Microstructures of porous inorganic membranes and permeation properties through those membranes were reviewed for amorphous silica membranes and zeolite membranes. Silica membranes were compared by the permeation properties of hydrogen such as activation energies or selectivities over nitrogen or helium. The activation energies of hydrogen through silica membranes prepared by the sol-gel method and the CVD method were the same level, and relatively loose or dense structure can be made by both methods. The effects of intercrystalline pathways on the permeation properties through zeolitic membranes were investigated. The intercrystalline pathways were filled by coking of a hydrocarbon or counterdiffusion CVD method. The permeation properties through intercrystalline pathways were explained by an i-i model. According to this model, ethanol was permselective from ethanol aqueous solution through intercrystalline pathways of the MFI zeolite membrane.

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Biomembranes have been modeled as a complex of lipid bilayer sheet embedding various membrane proteins. The lipid bilayer is assumed to be in liquid disordered state and hence, the lipid composition is uniform everywhere within the membrane. However, recent studies have revealed the existence of lipid raft, a lipid microdomain consisting of sphingolipids and cholesterol, in the outer leaflet of the cell membrane. Within the raft lipids are in liquid-ordered state and their mobility is strongly suppressed. The raft seems to serve as a platform where glycosil phosphatidylinositol (GPI) -or acyl chain-anchored proteins interact with each other thereby participating in intracellular signaling events and other cellular activities. Easily coalescing nature of rafts, when raft-residing proteins are cross-linked, may be important in raft function. The lipid bilayers may be better described as a mosaic of small domains.

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Present status of the porous membranes produced by the stretching methods was summarized. Following the general description of the stretching method, the structure, function, application and the direction of future development for the porous PTFE membranes were described. Recent studies of the mechanism of structure formation by uniaxially and biaxially stretched membranes and the effect of heat treatment were explained.

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The preparation conditions of polyimide (PI) asymmetric membranes on the nonwoven fabric have been investigated. The polyimide membranes were prepared by the phase inversion process in water coagulation bath using the casting solutions composed of polyimide, N, N'-dimethylacetamide (DMAc) as a rich solvent and 1, 4-dioxane (DOx) as a poor solvent. The N₂ permeability of polyimide membranes showed 10^-5-10^-9 [mol/ (m²·s·Pa)]. It was found that polyimide membranes can be utilized as a supporting membrane. And, the polyimide membranes prepared from the casting solution of 25wt% polyimide, 56.3wt% DMAc and 18.7wt% dioxane showed high benzene permselectivity (α =30) for the benzene/ cyclohexane (50vol%/50vol%) solution at 30°C on pervaporation.

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The membranes from agarose permeated water from aqueous organic mixtures, such as H₂O/MeOH, H₂O/EtOH, H₂O/1-PrOH, H₂O/2-PrOH, and H₂O/AAc. Especially, permselectivity toward water in H₂O/2-PrOH mixtures reached 5.0 × 10³ with the flux value of 20.0 g m^-2 h^-1. It was made clear that agarose can be applicable as one of promising membrane materials for the dehydration of water miscible organics.

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Compact unit system is commercially provided for cut treatment of turbidity and bacteria in water from general source. Equipping with newly developed high performance hollow fiber ultrafiltration (UF) membrane in this system, compact system design can be succeeded to obtain high water quality and very stable operation in long term only with periodical back washing of the hollow fibers. Cellulose Acetate is selected as a membrane material of the hollow fiber in order to give the fiber anti-membrane fauling and easy cleaning natures because of its hydrophilicity. Furthermore high membrane water flux performs well not only on the water production but also on the effective back washing by asymmetric membrane structure designed very highly. This unit system is expected economically benefit from applying to the small and middle classed water purification market.

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