Environmental pollution by organic solvents in both liquid and vapor phases, such as trichloroethylene, toluene, gasoline and so on, is now serious problem in the world. Membrane separation technology will be useful tool for controlling the pollution, and the research on membrane materials and development of solvent recovery process have just started.
In this review, air and water pollution at this moment will be surveyed, and the membrane separation technology applicable for the control, that is pervaporation, vapor permeation and reverse osmosis, will be summarized. The membrane separation data reported with various types of membranes, mainly rubber membranes, for organic chlorine compounds and organic solvents, such as toluene, benzene, acetone etc., will be reviewed.

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The ability of bilayer lipids to form interdigitated states, in which the acyl chains from opposing monolayers interdigitate, has recently come into focus as a means to significantly alter membrane properties. In addition to changing the membrane thickness and the hydrophobic region of bilayer membranes, the formation of interdigitated membranes alters the electrostatic properties of the membrane surface. A variety of molecules can induce the formation of a fully interdigitated phase by saturated symmetric phospholipids. They include amphipathic molecules such as polyols, short chain alcohols, anesthetics and so on. Common properties are that they do not penetrate too deeply into the hydrocarbon core of bilayer membranes and that they are capable of displacing some of the water molecules associated with the head groups of lipids, thereby creating an increase in the surface area of these groups.
In the present review, the forces governing the self-assembly of lipid molecules into interdigitated structures, the physical properties distinctive of interdigitated state membranes and fruitful methods by which interdigitation in membranes may be determined and characterized are outlined along with a detection method developed by the author and coworkers. Mechanisms of phase transition of lipid membranes in the presence of ethanol as an inducer are also proposed and covered together with the results of research concerning the effects of cholesterol on the formation of interdigitated membranes. The possibility of producing formation of interdigitated structures in biomembranes is discussed.

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Interfacial equilibria among various liquid-crystalline structures of lipid and lipid mixtures are reviewed and the physiological relevance of the equillibria is discussed. Phospholipid-neutrallipid mixtures form various liquidcrystalline structures, including bilayers, micelles, emulsions, reverse hexagonal and reverse cubic structures. Neutral lipids, such as triglycerides, cholesterylesters and ubiquinone-10 have very limited solubilities in bilayers of phosphatidylcholine (PC). Excess amount of neutral lipid is separated from the bilayers and forms the droplets in an aqueous medium. The droplets are covered by the PC monolayers spread from the bilayers, and are stabilized as emulsion particles. Lipoproteins, chylomicrons and very low density lipoproteins, in animal plasma are such particles containing a very small amount of several different apoproteins. The lipid composition of emulsions influences the affinity to apoproteins in plasma, and controls the catabolism of the particles in vivo.
Some other neutral lipids, such as diglycerides, monoglycerides, α-tocopherol and menaquinone-4 have large solubilities in the PC bilayers. Addition of such a neutral lipid to the bilayers occasionally induces formation of irregular structures (intrabilayer-particles or-micelles) and vesiculation of the bilayers. The intrabilayer-structures are considered to be precursors for reverse hexagonal and re-verse cubic structures. Diglycerides and α-tocopherol in the PC bilayers activate phospholipases A₂, C and D.

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Recent advances in the studies of micelle-vesicle transition were reviewed. Common phenomena appeared in the transition process were extracted from among a variety of data, which seemingly confricted with each other, because of their different phospholipids, detergents or detergent-removal methods. A 4 stages model was proposed than the 3 stages model. In the first stage, detergent is simply removed from the mixed micelles resulting in the glowth of the micellar size. In the second stage, micelle to vesicle (SUV*) transition occurs. In the third stage, postvesiculation size glowth from SUV* to LUV occurs by a fusion or a phospholipid transfer. In the fourth stage, detergent is simply removed resulting in the decrease of the vesicle size. Vesicle destruction is basically symmetrical opposite of the vesicle formation process. The 4 stages model, developed here, not only solved the contradiction among data obtained by many investigators, but also suggested a new method of vesicle size regulation in vesicle preparation process.

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To develop a new blood compatible polymer, it is important to evaluate blood-material interactions carefully. In this review article, the evaluation of blood compatibility of a polymer containing a phospholipid polar group, poly (2-methacryloyloxyethyl phosphorylcholine (MPC) -co-n-butyl methacrylate (BMA)), with human whole blood and its application for medical membrane were reported. When human whole blood without an anticoagulant was contacted with polymers, the blood cell adhesion and aggregation on the polymer without the MPC moiety was extensive, and considerable fibrin deposition was observed. The MPC moiety in the copolymer plays an important role in the nonthrombogenic behavior of the copolymer. The adsorption of phospholipids and proteins from human plasma on poly (MPC-co-BMA) was investigated to clarify the mechanism of the nonthrombogenicity observed on the polymer. The amount of phospholipids was increased; whereas, adsorbed proteins were decreased with an increase in the MPC composition. From these results, it is concluded that the phospholipids adsorbed on poly (MPC-co-BMA) play the most important role in the nonthrombogenicity of the MPC copolymer. By use of the protein adsorption resistance property observed on poly (MPC-co-BMA), the stability of membrane performance in blood contacting circumstance or in living organisms could be improved. For example, responsibility of blood glucose sensor covered with poly (MPC-co-BMA) membrane was not reduced even after 7 days implantation in subcutaneous of rat. Therefore, it can be considered that the MPC copolymers have excellent potential to improve blood compatibility, protein adsorption resistibility on every medical membrane and device.

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A series of cellulose acetate (CA) particles have been prepared by spraying method from the solutions containing different concentrations of phosphoric acid and CA. The pore sizes of particles obtained have been tested by means of gel chromatography using polyethylene glycol (PEG) with different molecular weights as molecular size probes. It is found that phosphoric acid additive acts as a pore adjusting solvent to from a suitable porosity in CA particles. At low CA concentration (5 wt%) the pore sizes decrease with phosphoric acid in a certain concentration, and at high CA concentration (17 wt%) the pore sizes increase by adding phosphoric acid additive. The water contents of particles and the stationary water contents in chromatographic columns have also been analysized. The results show that both the water contents and stationary water contents for prepared particles are larger than those for original CA powder and increase to a maximum in a certain pore sizes of particles. The equilibrium distribution coefficients (Kd) for aliphatic alcohols, acids and amines have been measured. The Kd values of original CA powder for all these organics are larger than those of prepared CA particles, especially for longer carbon chains of organics. We also found that the structure of prepared particles have some effects on the Kd values for the organics with longer carbon chains, but almost no effects for the organics with short carbon chains.

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