Surfactant
Definition:
Short for "SURFace ACTive AgeNT". A surfactant is a molecule with an
amphiphilic character that has a tendency to accumulate at interfaces.
Summary/Description
Surfactants is a larger class of molecules which have a significant
technological and biological importance. Generally these molecules
consist of a hydrophilic (water soluble) and a hydrophobic (water
insoluble) part. This amphiphilic nature of surfactants is responsible
for their association behaviour in solution (micelles, bilayers,
vesicles, etc.) and their accumulation at interfaces (gas/liquid,
liquid/liquid or liquid/solid). The hydrophobic part usually consists
of hydrocarbon or fluorocarbon chains, while the hydrophilic part
consists of a polar group (-OH, -COOH, -NH3+, -PO4-(CH2)2NH3+ etc.).
The association behaviour of surfactants in solution and their
affinity for interfaces is determined by the physical and chemical
properties of the hydrophobic and hydrophilic groups, respectively. The
size and shape of the hydrocarbon moiety and the size, charge and
hydration of the hydrophilic head group are of utmost importance in
this respect. Depending on the balance between these properties a wide
variety of self-assembled structures, both at interfaces and in bulk,
have been observed. The driving force behind the association is the
reduction of the free energy of the system. Therefore, when a
surfactant comes in contact with water it accumulates at the air/water
interface causing a decrease in the surface tension of water.
Surfactants are the active ingredients in soap, since the
hydrophobic component sticks to grease and dirt while the hydrophilic
section sticks to the water.
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