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Semipermeable membrane
 
 
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A semipermeable membrane, also termed a selectively-permeable membrane, a partially-permeable membrane or a differentially-permeable membrane, is a membrane that will allow certain molecule
Molecule

In chemistry, a molecule is defined as a sufficiently stable, electric charge neutral group of at least two atoms in a definite arrangement held together by very strong chemical bonds....
s or ion
Ion

An ion is an atom or molecule which has lost or gained one or more electrons, giving it a positive or negative electrical charge. According to the Bohr_model this will be from or in the outer shield 'n'....
s to pass through it by diffusion
Diffusion

Molecular diffusion, often called simply diffusion, is a net transport of molecules from a region of higher concentration to one of lower concentration by random molecular motion....
 and occasionally specialized "facilitated diffusion
Facilitated diffusion

Facilitated diffusion is a process of diffusion, a form of passive transport facilitated by transport proteins. Facilitated diffusion is the spontaneous passage of molecules or ions across a biological membrane passing through specific transmembrane transport proteins....
." The rate of passage depends on the pressure
Pressure

Pressure is the force per unit area applied to an object in a direction surface normal to the surface. Gauge pressure is the pressure relative to the local atmospheric or ambient pressure....
, concentration
Concentration

In chemistry, concentration is the measure of how much of a given chemical substance there is mixed with another substance. This can apply to any sort of chemical mixture, but most frequently the concept is limited to homogeneous solutions, where it refers to the amount of solute in the solvent....
, and temperature
Temperature

In physics, temperature is a physical property of a Physical system that underlies the common notions of hot and cold; something that feels hotter generally has the greater temperature....
 of the molecules or solutes on either side, as well as the permeability of the membrane to each solute.






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Semipermeable Membrane
A semipermeable membrane, also termed a selectively-permeable membrane, a partially-permeable membrane or a differentially-permeable membrane, is a membrane that will allow certain molecule
Molecule

In chemistry, a molecule is defined as a sufficiently stable, electric charge neutral group of at least two atoms in a definite arrangement held together by very strong chemical bonds....
s or ion
Ion

An ion is an atom or molecule which has lost or gained one or more electrons, giving it a positive or negative electrical charge. According to the Bohr_model this will be from or in the outer shield 'n'....
s to pass through it by diffusion
Diffusion

Molecular diffusion, often called simply diffusion, is a net transport of molecules from a region of higher concentration to one of lower concentration by random molecular motion....
 and occasionally specialized "facilitated diffusion
Facilitated diffusion

Facilitated diffusion is a process of diffusion, a form of passive transport facilitated by transport proteins. Facilitated diffusion is the spontaneous passage of molecules or ions across a biological membrane passing through specific transmembrane transport proteins....
." The rate of passage depends on the pressure
Pressure

Pressure is the force per unit area applied to an object in a direction surface normal to the surface. Gauge pressure is the pressure relative to the local atmospheric or ambient pressure....
, concentration
Concentration

In chemistry, concentration is the measure of how much of a given chemical substance there is mixed with another substance. This can apply to any sort of chemical mixture, but most frequently the concept is limited to homogeneous solutions, where it refers to the amount of solute in the solvent....
, and temperature
Temperature

In physics, temperature is a physical property of a Physical system that underlies the common notions of hot and cold; something that feels hotter generally has the greater temperature....
 of the molecules or solutes on either side, as well as the permeability of the membrane to each solute. Depending on the membrane and the solute, permeability may depend on solute size, solubility
Solubility

Solubility is often seen as a property of a substance; for instance the solubility of a solid substance usually refers to the concentration of the substance in a liquid that has reached equilibrium with the substance in solid phase ....
, properties, or chemistry. An example of a semi-permeable membrane is the lipid bilayer
Lipid bilayer

A lipid bilayer is a thin membrane made of two layers of lipid molecules. These membranes are flat sheets that form a continuous barrier around cell ....
, on which is based the plasma membrane that surrounds all biological cell
Cell (biology)

The cell is the structural and functional unit of all known Life organisms. It is the smallest unit of an organism that is classified as living, and is often called the building bricks of life....
s. Many natural and synthetic materials thicker than a membrane are also semipermeable. An example of this is the thin film on the inside of an egg
Egg (biology)

In most birds and reptiles, an egg is the zygote, resulting from fertilization of the ovum. To enable incubation the egg is usually kept within a favourable temperature range as it nourishes and protects the growing embryo....
.

One example of a semipermeable membrane is a phospholipid bilayer, a group of phospholipids (consisting of a phosphate head and two fatty acid
Fatty acid

In chemistry, especially biochemistry, a fatty acid is a carboxylic acid often with a long unbranched aliphatic tail , which is either saturation or Unsaturated compound....
 tails) arranged into a double-layer, with the hydrophilic phosphate heads exposed to the water content outside and within the cell and the hydrophobic tails hidden in the inside. The phospholipid bilayer is the most permeable to small, uncharged solutes. Protein channels float through the phospholipids, and, collectively, this model is known as the fluid mosaic model.

In the process of reverse osmosis
Reverse osmosis

Reverse osmosis is a filtration process typically used for water. It works by using pressure to force a solution through a semi-permeable membrane, retaining the solute on one side and allowing the pure solvent to pass to the other side....
, thin film composite membrane
Thin film composite membrane

Thin film composite material artificial membrane are semipermeable membranes manufactured principally for use in water purification or desalination systems....
s (TFC or TFM) are used. These are semipermeable membranes manufactured principally for use in water purification
Water purification

This article discusses large scale, municipal water purification. For portable/emergency water purification, see Portable water purification.Water purification is the process of removing undesirable chemical and biological contaminants from raw water....
 or desalination
Desalination

Desalination, desalinization, or desalinisation refers to any of several processes that remove excess sodium chloride and other minerals from water....
 systems. They also have use in chemical applications such as batteries and fuel cells. In essence, a TFC material is a molecular sieve constructed in the form of a film from two or more layered materials.

Membranes used in reverse osmosis are, in general, made out of polyimide
Polyimide

Polyimide is a polymer of imide monomers. The structure of imide is as shown.Thermosetting polyimides are commercially available as uncured resins, stock shapes, thin sheets, laminates and machines parts....
, chosen primarily for its permeability to water and relative impermeability to various dissolved impurities including salt ions and other small molecules that cannot be filtered. Another example of a semipermeable membrane is dialysis tubing
Dialysis tubing

Dialysis Tubing is a type of Semipermeable membrane tubing made from regenerated cellulose or cellophane. It is used for diffusion, or more accurately osmosis....
.

Other types are cellulose ester membrane (CEM), charge mosaic membrane (CMM), bipolar membrane (BPM), anion exchange membrane (AEM).

See also

  • ADME
    ADME

    ADME is an acronym in pharmacokinetics and pharmacology for absorption , distribution , metabolism, and excretion, and describes the disposition of a pharmaceutical Chemical compound within an organism....
  • Artificial membrane
    Artificial membrane

    Artificial membrane also known as synthetic membrane is a syntheticly created membrane which is usually intended for separation purposes in laboratory or in industry....
  • Barrer
    Barrer

    A Barrer is a non-SI unit of gas Semipermeable membrane used in the contact lens industry. It is a bulk property. It is named after Permeation#Richard Barrer .281910 - 1996.29....
  • Osmosis
    Osmosis

    Osmosis is the diffusion of a solvent through a Semipermeable membrane, from a solution of low solute concentration to a solution with high solute concentration , up a solute concentration gradient....
  • Reverse osmosis
    Reverse osmosis

    Reverse osmosis is a filtration process typically used for water. It works by using pressure to force a solution through a semi-permeable membrane, retaining the solute on one side and allowing the pure solvent to pass to the other side....
  • Diffusion
    Diffusion

    Molecular diffusion, often called simply diffusion, is a net transport of molecules from a region of higher concentration to one of lower concentration by random molecular motion....


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