Surfactents

DEFINITION

Surfactants are compounds that lower the surface tension of a liquid, allowing easier spreading, and lowering of the interfacial tension between two liquids, or between a liquid and a solid. Surfactants may act as: detergents, wetting agents, emulsifiers, foaming agents, and dispersants.

Etymology

The term surfactant is a blend of surface active agent.[1] Surfactants are usually organic compounds that are amphiphilic, meaning they contain both hydrophobic groups (their tails) and hydrophilic groups (their heads)

Substances that don’t dissolve in water are hydrophobic.Substances that are miscible in water are hydrophilic.

Example:

Sodium stearate is a typical dual-nature molecule. It has an ionic, hydrophilic polar head and a hydrophobic nonpolar tail.     

Properties

1.Micelle

A micelle—the lipophilic tails of the surfactant molecules remain on the inside of the micelle due to unfavourable interactions. The polar “heads” of the micelle,due to favourable interactions with water, form a hydrophilic outer layer that in effect protects the hydrophobic core of the micelle. The compounds that make up a micelle are typically amphiphilic in nature, meaning that not only are micelles soluble in protic solvents such as water but also in aprotic solvents as a reverse micelle.

i.                    Critical micelle concentration:

 The concentration at which surfactants begin to form micelles is known as the critical micelle concentration (CMC).

2.Surface Tension Reducing Property:

Surfactants reduce the surface tension of water by adsorbing at the liquid-gas interface. They also reduce the interfacial tension between oil and water by adsorbing at the liquid-liquid interface.

3.Aggregates formation:

Many surfactants can also assemble in the bulk solution into aggregates.

Examples of such aggregates are

i:vesicles

ii. micelles.

4. Thermodynamics Behavior:

Thermodynamics of the surfactant systems are of great importance, theoretically and practically.[2] This is because surfactant systems represent systems between ordered and disordered states of matter. Surfactant solutions may contain an ordered phase (micelles) and a disordered phase (free surfactant molecules and/or ions in the solution).

5. Detergency

The function of detergency or cleaning is a complex combination of all the previous functions. The surface to be cleaned and the soil to be removed must initially be wet  and the soils suspended, solubilised, dissolved or separated in some way so that the soil will not just re-deposit on the surface.