Although this problem is too profound, so far scientists have given some explanations. In fact, we can understand the "infiltration phenomenon" clearly. The following four theories are popular in the academic circles for the explanation of "osmosis separation mechanism":
Forward osmosis method The latest modern unified model Deng Yumen's "dry closed wet open model" in the 1990s
Dry closed wet open model
When the membrane is dry, the membrane pore shrinks compactly, Pore closure , no dry preparation can be seen under the electron microscope Microscopic examination Of“ No hole ”Dry membrane ； When the membrane is wet, the membrane material swells, and the pores of the membrane are swelled by solvent, The hole is open. Merging is "Dry closed wet open" desalination model.
And early representative
Principle and characteristics of forward osmosis membrane separation
The forward osmosis membrane separation technology is similar to the reverse osmosis separation technology. It is the diffusion of water molecules from one side of the semipermeable membrane to the other side to intercept solute molecules and ions. Different from the pressure driven membrane separation process, the driving force of forward osmosis is the osmotic pressure difference Act on both sides of the semipermeable membrane, not the external pressure, as shown in Figure 1.
In the process of forward osmosis, water molecules diffuse from the side with high chemical potential of the selective permeation membrane to the side with low chemical potential, while pressure delayed osmosis is an intermediate process between forward osmosis and reverse osmosis. Water pressure acts in the opposite direction of the osmotic pressure gradient, and the net flux of water is still in the direction of concentrated solution.
With the rapid development of science and technology, pressure driven Reverse osmosis membrane The separation technology (RO) has made great innovation and improvement in membrane, membrane assembly, equipment and process, but people are increasingly aware that RO technology energy conservation . Limitations in the field of environmental protection. In terms of desalination, RO technology can be considered to be close to the peak of development. Therefore, in recent years, foreign countries have carried out“ Forward osmosis membrane separation technology (FO) " Has been applied in seawater desalination, sewage treatment, food processing, medicine and other fields, especially“ Pressure delayed osmosis (PRO) seawater electricity generation ”It is also a promising clean renewable energy development technology J. However, little attention has been paid to forward osmosis membrane separation technology in China, and there are few related studies and papers. Although, in the 1990s, China had creative inventions“ Seawater desalination by non pressurized adsorption infiltration ”（CN92110710.2）。 Forward osmosis separation technology has been applied for a long time. Long ago, people used salt to store food for a long time, because most bacteria, molds and pathogens would die of dehydration or lose their activity temporarily due to osmosis in a high salt environment. Nowadays, people have begun to use forward osmosis membrane separation technology Seawater desalination , industrial wastewater treatment, landfill leachate treatment, etc; The food industry uses forward osmosis membrane separation to concentrate drinks in the laboratory; Emergency rescue Life support system Fresh water is produced by forward osmosis membrane separation technology. Recently, with the development of material science, forward osmosis technology has been applied to human medicine control Release. Non pressurized Osmosis (1990s)
The non pressurized adsorption osmosis seawater desalination method, or "forward osmosis method", allows water to enter a super absorbent adsorbent or a solution or solid with salt concentration even higher than that of sea water through the forward osmosis of porous membrane, without external pressure, but the special salt "extract" in the solution is easy to evaporate, and does not need to add too much heat (the energy ratio of heating energy and reverse osmosis pressure is?) 。 It is divided into solid salt and liquid salt directions. Solid salt desorption consumes less energy.
seawater desalination technology : Non pressurized adsorption infiltration desalination method (CN92110710.2) 1992: Deng Yu's invention , American Chemical Abstracts. The other two methods are innovative and improved in the film structure
One uses carbon nanotubes to make holes in the film, and the other
Protein membrane of living cells
The pores of the membrane are composed of proteins that guide water molecules through the cell membrane of living cells.
Osmosis, reverse osmosis - an important member of reverse osmosis.
The broad concept of penetrant refers to a kind of chemicals that can help the substances to be permeated penetrate into the substances to be permeated, which are generally used in industry surface active agent (can be anionic or non-ionic) or organic or inorganic solvents. Solute is the substance dispersed in the solution called solute, and the medium in which solute is dispersed is called solvent. This distinction is essentially based on its relative content in the mixture, which is not very strict, so it is not absolute. However, for the solution composed of gas or solid substance and liquid, no matter how much liquid is, the liquid is generally called solvent. The solute is generally evenly distributed in the solvent in the form of molecule, atom or ion. The diameter of solute particles (such as sucrose molecules in sugar water, chloride ions and sodium ions in sodium chloride solution, iodine molecules in iodine wine) is generally less than 1 nm. Dissolved substances such as granulated sugar are called solutes. Both include solid, liquid and gas.
The medium in which solute is dispersed is called solvent. Solute and solvent are relative. When two liquids dissolve each other, the one with more is called solvent, and the one with less is called solute. For example, when alcohol and water dissolve each other, generally alcohol is solute and water is solvent. If a small amount of water is dissolved in alcohol, water can also be used as solute and alcohol as solvent. Generally, water is always used as solvent in aqueous solution. The most widely used solvent is water. Solvents are polar solvents (high dielectric constant) and Non-polar solvent (low dielectric constant). The most typical polar solvent is water, and non-polar solvents such as hydrocarbons. Aromatic hydrocarbons (such as benzene) are more soluble than aliphatic hydrocarbons (such as gasoline). Many organic substances are also used as solvents, often referred to as organic solvents, such as alcohols, ethers, ketones and halogenated hydrocarbons, chemical industry Produce a large number of organic solvents, which are used in coatings, plastics synthetic rubber It has a wide range of applications. The full name of penetrant (JFC) is Fatty alcohol polyoxyethylene ether , genus Nonionic surfactant 。 Penetrant, as its name implies, is a substance that plays the role of permeation and has fixed hydrophilic and lipophilic groups, can be directionally arranged on the surface of the solution, and can significantly reduce the surface tension. Penetrants are generally divided into two categories: nonionic and anionic. Non ionic ones include JFC, JFC-1, JFC-2, JFC-E, etc; Anionic Rapid Penetrant T 、 Alkali resistant penetrant OEP-70 , alkali resistant penetrant AEP, high-temperature penetrant JFC-M, etc. Osmosis is the phenomenon that two solutions with different concentrations are separated by a semipermeable membrane (a membrane that allows solvent molecules to pass through, but does not allow solute molecules to pass through), and water molecules or other solvent molecules enter the solution with high concentration from the solution with low concentration through the semipermeable membrane. Or the phenomenon that water molecules move from the side with high water potential to the side with low water potential through the semipermeable membrane. plant cell The vacuoles of are filled with aqueous solution. If the vacuole membrane and plasma membrane are regarded as semipermeable membranes, infiltration will occur between cells, or when cells are immersed in solution or water. In fact, biomembrane is not an ideal semi permeable membrane. It is a selective permeable membrane, which allows both water molecules and some solutes to pass through, but usually allows solvent molecules to pass through much more than solute molecules, so infiltration can occur. Due to the existence of cell wall, plant cells can generate pressure to gradually equalize the water potential inside and outside the cell, and the cell stops Imbibition 。 Therefore, plant cells generally do not break when placed in water. Animal cell If red blood cells are put into water, they will break. Conditions for seepage
Semipermeable membrane, concentration difference inside and outside cells
Permeation experiment
Fasten the broad bean seed coat to the funnel, inject sucrose solution, and then immerse the whole device into a beaker containing clear water, with the liquid level inside and outside the funnel equal. Since the broad bean seed coat is close to a semi permeable membrane (i.e. a membrane that allows water molecules to pass but cannot be penetrated by sucrose molecules), the whole device becomes a permeation system. In an osmotic system, the direction of water movement depends on the water potential of solutions on both sides of the semipermeable membrane. The water of the solution with high water potential flows to the solution with low water potential. In fact, the water molecules on both sides of the semipermeable membrane can pass freely, but the water potential of clear water is high and the water potential of sucrose solution is low. There are more water molecules from clear water to sucrose solution than from sucrose solution to clear water. Therefore, in appearance, the water in the beaker flows into the funnel, the liquid level in the glass tube in the funnel rises, and the hydrostatic pressure begins to increase. As the water gradually enters the glass tube, the liquid level rises and the hydrostatic pressure increases. The compressed water moves faster from the glass tube to the beaker, and the speed of water in and out of the membrane is closer and closer. Finally, the liquid level will no longer rise and stay still, which means that the speed of water in and out is equal and in dynamic equilibrium. The phenomenon that water moves from the system with high water potential to the system with low water potential through the semipermeable membrane is called osmosis.
Permeation and Swelling and Permeation Mechanism
Infiltration and Imbibition The process by which a hydrophilic gel absorbs water molecules and expands them. It is a nonliving physical process. Plant tissues contain many such substances, such as cellulose, pectin, starch and protein, which have strong hydrophilicity. When they are not saturated with water, they have a strong potential to absorb water. The most obvious example is air dried seeds, because they store a lot of protein or starch. The binding trend of protein and water is greater than that of starch, so the imbibition of legume seeds is very obvious. The imbibited object expands due to the adsorption of water molecules, and its pressure is very large. For example, if the dry seeds are filled with rock cracks, the imbibition pressure generated by its water absorption can cause rock fracture.
The way plants absorb water
Plants absorb water in two ways: imbibition and osmosis.
There is no vacuole in the swelling effect plant cell The way to absorb water, such as cells at growth points, stem seed cells, etc., is based on the principle that there are a large number of hydrophilic substances in the cells, which can absorb a large amount of water from the outside world. Living cells and dead cells can absorb water through swelling. Osmotic action is the way that mature plant cells with vacuoles absorb water. The principle is: Protoplast have Selectivity There is a concentration difference between the solution inside and outside the protoplast layer, so water molecules can diffuse from the side with low concentration to the side with high concentration through the protoplast layer. The osmotic pressure of the solution is related to the amount of solute molecules in the solution. The more solute molecules in the solution, the higher the osmotic pressure, and vice versa. When comparing the osmotic pressure of the two solutions, take the amount of solute molecules in the two solutions as the standard for comparison. If the solute molecules are the same, the mass fraction can also be compared. The cell that can absorb water through osmosis must be a living cell. A mature plant cell is an osmotic system. The best example to verify the absorption or loss of water through osmosis is the separation of mass wall and Plasmolysis restoration Experiment. Excessive fertilization at one time causes "seedling burning", which is due to the sudden increase in the concentration of soil solution, which makes it difficult or impossible for the root cells of plants to absorb water. One of the reasons why most crops in saline alkali land cannot grow normally is that the concentration of soil solution is too high. The submerged fish and meat are not easy to deteriorate, because the high concentration of salt solution makes the cells and other microorganisms lose water and die. 
