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Schematic of size based membrane exclusion

A membrane is a layer of material which serves as a selective barrier between two phases and remains impermeable to specific particles, molecules, or substances when exposed to the action of a driving force. Some components are allowed passage by the membrane into a permeate stream, whereas others are retained by it and accumulate in the retentate stream.[1]

Membranes can be of various thickness, with homogeneous or heterogeneous structure. Membrane can also be classified according to their pore diameter. According to IUPAC, there are three different types of pore size classifications: microporous (dp < 2nm), mesoporous (2nm < dp < 50nm) and macroporous (dp > 50nm).[2] Membranes can be neutral or charged, and particles transport can be active or passive. The latter can be facilitated by pressure, concentration, chemical or electrical gradients of the membrane process. Membranes can be generally classified into three groups: inorganic, polymeric or biological membranes. These three types of membranes differ significantly in their structure and functionality.[3]

Contents

Biological

Artificial

Polymeric

See also

References

  1. ^ Zydney, Andrew L.; Zeman, Leos J. (1996). Microfiltration and ultrafiltration: principles and applications. New York: CRC. ISBN 0-8247-9735-3.  
  2. ^ Macroporous Materials Containing Three Dimensional Periodic Structures
  3. ^ Mulder, Marcel (1996). Basic principles of membrane technology (2 ed.). Kluwer Academic: Springer. ISBN 0-7923-4248-8.  
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Simple English

A membrane is a thin soft layer of material. A membrane separates two things.

In biology a membrane can be mean two things: a tissue or plasma membrane. Plasma membranes are very small. Tissue membranes are bigger.

Membrane as tissue

A membrane can mean a thin layer of cells or tissue. This layer covers, separates, or lines a tissue or organ. An example is the mucous membrane that is the skin that lines the inside of your nose and mouth.

Plasma membranes

The plasma membrane covers cells. Plasma membranes also divide the cell into different spaces called organelles. Organelles are special areas of the cell that do different work. For example, the nucleus holds the DNA in a cell. The mitochondria make energy for the cell.

Plasma membranes are made of lipids (fats) and protein. The lipids keep the inside of the cell separate from the outside. The proteins do many things. They give the cell messages from outside. They let some things (like glucose, calcium, and potassium) go into and out of the cell.



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