Semi permeability, physical property, refers to the property that small holes or holes in an object can only allow some things to pass through, but not others.The property of membrane or membrane structure that only allows the penetration of solvent (usually water) or some solutes, but not other solutes.M. Tra ube (1867)Cupric ferrocyanideThe precipitation membrane of W.Pfeffer is an almost ideal semipermeable membrane, which is used for the penetrometer of W.Pfeffer.
The property that a small hole or hole in an object can only allow some things to pass through, but not others
The property of membrane or membrane structure that only allows the penetration of solvent (usually water) or some solutes, but not other solutes.M. Tra ube (1867)Cupric ferrocyanideThe precipitation membrane of W.Pfeffer is an almost ideal semipermeable membrane, which is used for the penetrometer of W.Pfeffer.[1]
principle
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Since H. De Vries (1871) discovered the cell semipermeability, it has been attributed tocell membraneIn essence, cell membrane can be regarded as semipermeable membrane, but strictly speaking, it is just that the penetration rate of solute is significantly lower than that of solvent.The degree of semi permeability of a certain membrane to a certain solute can be expressed by the size of reflection coefficient σ.If the pressure gradient necessary to prevent water flow caused by the concentration gradient △ Cs of solute passing through the membrane is set as △ P, σ can be obtained by σ=△ P/(RT △ Cs) (R is the gas constant, T is the absolute temperature).This is the ratio of apparent osmotic pressure to theoretical osmotic pressure (Staverman, 1951). When the semipermeable membrane is perfect, σ is 1. When the semipermeability is reduced, σ becomes less than 1.The degree of semipermeability of cell membrane can change according to physiological conditions such as excitation (seeMembrane potential）。In addition, cells also have a functional structure (active transport) that can not be penetrated into the cell by the substances through the membrane.This semipermeability of cell membrane is also called selective permeability.[1]
Semipermeable membrane
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Semipermeable membrane (English: semipermeable membrane) is a kind of membrane that only allows certain molecules or ions to diffuse in and outparticleThe pass of hasselectivityFilm.Such as cell membrane, bladder membraneparchmentAnd artificial collodion film, etc.Modern semi permeable membranes are also used for porous walls (such as unglazed ceramics) and are made by depositing appropriate compounds (such as copper ferricyanide) in their pores.Semi permeable membrane for penetration of sol and determinationOsmotic pressureEtc.Biological absorption of nutrients is also carried out through semi permeable membrane.Reverse osmosis (RO) for pure water is a semi permeable membrane made of polymer materials through special processes. It only allows water molecules to pass through, but not solutes.When the pressure of raw water on one side of the semi permeable membrane exceeds the osmotic pressure with a high-pressure pump, the water molecules in the raw water can pass through the semi permeable membrane and enter the other side to obtainpurified water。The dissolved and insoluble inorganic salts, heavy metal ions, organic substances in raw water,Thallus，colloidSuch substances cannot pass through the semi permeable membrane and can only be left in concentrated water to be discharged.Reverse osmosis equipmentIt is widely used in pharmaceutical industry, beverage industry, electronics, power industry, etc.[2]
application
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Parchment semipermeable membrane
holdQuantitative filter paperPut it into a beaker containing 2:1 water sulfuric acid, press it gently with a glass rod to make it immersed evenly (neither the glass rod nor the filter paper can contain water).After soaking for 60~90s, take it out, immediately wash it with distilled water, then put it into 1:1 ammonia monohydrate aqueous solution (i.e. ammonia water), neutralize the residual acid, take it out and dry it in air.
1. The conical bottle used to make the rubber cotton semi permeable film must be dry, otherwise it is difficult to form the film.
2. The rubber cotton semi permeable membrane is easy to break, so please keep it in distilled water before the experiment.
3. When making parchment, the concentration of sulfuric acid and soaking time must be controlled, and the filter paper must not overlap during soaking.[1]
