Membranes osmosis

F. Paritosh, S. Murad. Molecular simulation of osmosis and reverse osmosis in aqueous electrolyte solutions. AIChE J 42 2984, 1996 S. Murad, K. Oder, J. Lin. Molecular simulation of osmosis, reverse osmosis, and electro-osmosis in aqueous and methanolic electrolyte solutions. Mol Phys 95 401, 1998 J. G. Powles, S. Murad. The molecular simulation of semi-permeable membranes—osmosis, reverse osmosis and electro-osmosis. J Mol Liq 75 225, 1998. 

Flotation Freeze drying Ion exchange Membranes Osmosis Zone melting... 

H. J. Oel (118) solved the flux equations, introducing many simplifications. He omitted the activity coefficients and assumed constant mobilities in the membrane and a constant concentration of active groups across the membrane. Osmosis was neglected. 

Any living skin tissue which is very, very thin is called a membrane. Like all living things, membranes are made of cells, the basic structural unit of plants and animals. Membranes seem to be strong and solid, but if you looked at one under a microscope, you would see that the walls of the cells are porous. Because of these pores, osmosis can take place. Osmosis is the process by which molecules pass through the pores in the cell walls of a membrane. Osmosis, in other words, is diffusion through a membrane. 

In Chapter 13, you learned that diffusion is the mixing of gases or liquids resulting from their random motions. Osmosis is the diffusion of solvent particles across a semipermeable membrane from an area of higher solvent concentration to an area of lower solvent concentration. Semipermeable membranes are barriers with tiny pores that allow some but not all kinds of particles to cross. The membranes surrounding all living cells are semipermeable membranes. Osmosis plays an important role in many biological systems such as kidney dialysis and the uptake of nutrients by plants. 

Because a cell membrane is selectively permeable, it is not always possible for solutes to pass through it in response to a concentration gradient. In such cases the solvent diffuses through the membrane. Such membranes, permeable to solvent but not to solute, are specifically called semlpermeable membranes. Osmosis is the diffusion of a solvent (water in biological systems) through a semlpermeable membrane in response to a water concentration gradient. 

The understanding of the thermodynamic behaviour of PEO in aqueous solutions is important for predicting the phase behaviour of these compounds and many of polyoxyethylene derivates. PEO has a wide application in technics, surface and colloid chemistry, medicine and pharmacy. The purpose of this work is, to determine the thermodynamic functions in a large range of concentration and temperature with the aid of vapour pressure (VPO) and membrane osmotic (MO) measurements. Furthermore we have used a differential measuring technique in TO, which is a modified steady state method w e have developed [l, 2]. A similar method was introduced in the membrane osmosis by Rehage and Meys C3]. 

PEO 2000 for synthesis (Merck-Schuchardt) was chosen for osmotic vapour pressure measurements. Fructose p.a. (Fa. Merck) was used as calibrating substance. For the membrane osmosis PEO 35000 (Hoechst AG) was taken. This product was fractionated by slowly cooling a solution (10 wt.% PEO) of a mixture water/acetone (15/85 wt./wt.). This procedure was carried out to make sure, that the sample doesn t contain portions of low molecular polymers <20000 g/mol. The membranes (Sartorius, Gottingen, regenerated cellulose Cat.-Nr. 11539) have a lower limit for determination of molar masses of 20000 g/mol. 

CoUigative Properties The presence of a solute affects the vapor pressure, boiUng point, and Ireezmg point of a solvent. In addition, when a solution is separated from the solvent by a semiper-meable membrane, osmosis, the passage of solvent molecules from the solvent to the solution, occurs. Equations have been derived that relate the extent of the changes in these properties to the concentration of the solution. 

He Z, He C, Zhang Z, Zou Z, Wang H (2007) Changes of antioxidative enzymes and cell membrane osmosis in tomato colonized by arbuscular mycorrhizae under NaCl stress. Colloids Surf B Biointerfaces 59 128-133... 

Catain membranes allow solvent molecules to pass through them but not solute molecules, particularly not those of large molecular weight. Such a membrane is called semipermeable and might be an animal bladder, a vegetable tissue, or a piece of cellophane. Figure 12.23 depicts the operation of a semipermeable membrane. Osmosis... 

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