What is a vacuum flask

A membrane (from Middle High German membrane "Parchment"; from Latin membrana "Skin" or membrane "Limb") is a separating layer, a thin skin.


A distinction is made between membranes that are used to separate mixtures of substances (semipermeable membranes, filtration membranes, separating membranes, permselective membranes) and membranes that are intended to generate or modify vibrations (vibration membranes, oscillation membranes), but also membranes as primary elements (elementary particles) of the universe.

A special feature of the membrane is its property of only absorbing tensile forces under load and being able to pass them on to their edges. This state of a membrane is also called membrane tension state. A very nice example of this condition is a soap bubble.

Separation membranes

They exist in the


With regard to the Diffusion properties a distinction is made :

  • completely impermeable, (impermeable)
  • partially impermeable (semi-permeable or better: selectively permeable)
  • be permeable in one direction.
  • completely permeable, (omnipermeable)

Life in its current form is inconceivable without semipermeable membranes, because every biological cell is surrounded by a membrane and must allow certain substances to pass through the membrane.

Artificial membranes for separation technology consist of polymers (polyethersulfone, polyacrylonitrile, cellulose acetate or thin layers of silicone on a polymer carrier) and are usually produced by casting thin films. Other manufacturing processes are interfacial condensation (aromatic polyamide on a carrier) or nuclear track etching (bombardment of thin polycarbonate films with heavy particles of an accelerator).

The separation process is based on the transport through pores (sieve mechanism, ultrafiltration, filtration), the different solubility and diffusion (gas separation, dialysis, pervaporation) or charge differences (electrodialysis). The driving forces for transport are differences in pressure (filtration), concentration / chemical potential (dialysis), temperature or load.

Important technical applications are the production of drinking water by reverse osmosis (around 7 million cubic meters annually worldwide), filtration in the food industry, the recovery of organic vapors, e.g. B. Gasoline vapor recovery and electrolysis for chlorine production. However, about 50% of the market is used in medicine: as an artificial kidney to remove toxic substances by washing blood and as an artificial lung by supplying oxygen to the blood without bubbles.

The most important research centers in the field of material separation with membranes in Europe are the GKSS Research Center Geesthacht, the Universities of Twente, Enschede and Calabria and the IEM UMR Institute in Montpellier. The European Network of Excellence on Manoscale-based Membrane Technology is also controlled from there.

Technical membranes are used as filter membranes z. B. as an osmosis membrane in the domestic water supply or in pervaporation.

Vibration membranes

They exist in the

  • Technique: vibration membrane
  • Biology: biomembrane

In case of Vibration properties A membrane can be used to generate, amplify, absorb, dampen or measure the vibration. The stimulation of membrane vibrations presupposes that there is a continuously acting external force, which is given by the tensile stress caused by an edge restraint. The vibration excitation can take place in very different ways, for example by the impact of airborne sound, z. B. eardrum, by striking with a mallet, for example in the case of membranophones, or by electrical means, for example by stimulating a loudspeaker membrane.

Such vibrating diaphragms play an extremely important role in acoustics in numerous areas, for example in electroacoustic transducers, where they are used to convert mechanical sound energy into electrical energy, e.g. B. the microphone, or vice versa to convert electrical energy into sound energy, z. B. with speakers or headphones, during the listening process, as well as with certain musical instruments, z. B. the membranophones.

In both biology and technology, membranes are used in a wide variety of applications and functions.

Technical vibration diaphragms are used as vibration diaphragms in microphones, loudspeakers, pressure gauges, pumps, musical instruments, etc.

Examples of membranes

  • Basement membrane
  • eardrum
  • Nictitating skin
  • Dialysis membrane
  • Hymen

See also

  • Double membrane - scientists from the GKSS research center in Geesthacht present a new process

Category: Soft Matter