The Surfactants : Definition

Definition :

" The surfactants are able to disperse oily main parts in water (cleanser power), to form foam, to stabilise emulsions and to further the interfaces moistening.

Surfactants molecules posess a 6 atoms of carbon chain which is hydrophob ('doesn't like water'), and have a polar group hydrophile (who has affinity with water).

Those molecules having both hydrophob and hydrophile parts are called "amphiphile".

The molecule can be schematised this way :

---------------------O hydrophile part
hydrophob part



Classification :

a) Anionic Surfactant :

----------------(-) the hydrophile part is anionic

Different kind of anionic surfactants :

> derivees of fat acids : RCOO-,Na+ ( R : long chain in C12 to C18 the more often) resulting from saponification of triglycerids (triester of glycerol and fat acid) of vegetal oils.

example : sodium palmitate: CH3-(CH2)14-COO- , Na+

Where do we find them ?

N.B : Soaps containing the sodium ion are tough (we find them in bar of soap), those with potassium ion are smooth (used in shave foams or as surfactants in creams).

> alkylsulfates : R-O- SO3
- R = long chain of carbon : (synthetic detergents )

exemple : ammonium dodecyl sulfate or ammonium lauryl sulfate :
C12H25 – O – SO3- , NH4+

Where do we find them ?

present in toothpaste, shampoos, bath and shower products …

b) Cationic Surfactant :

--------------------(+) the hydrophile part is cationic

Kind of Cationic surfactants :

> quaternar ammonium salts : RR1R2R3 N+, allergising and irritating for eyes and skin, are often associed with other kind of surfactnats to attenuate those effects.

They have interesting bactericids properties.

Where do we find them ?

Their conditioning properties make them enter in after-shampoos formulation.

example : cetyltrimethylammonium bromure : C16-H33 N+ (CH3)3 , Br -

c) Non-ionic Surfactant :

The hydrophile part is neutral but strongly polar. Those elements are biologically safe.

> sorbates or esters of sorbitol and fat acids

> sorbitan esters (sorbitan : C6H12O5), and fat acids

Where do we find them ?

in emulsions but also numerous shampoos for their cleanser and foaming power.

d) Amphotere or Zwitterionic Surfactants

They possess two groupments of opposite charge. Following the pH they are under a cationic form or an anionic form.

> derivatives of betaine

> amine acid and their derivative which are often used in cosmetology as co-surfactant (in addition to principal surfactants) to stabilize micro-emulsion.

They are excellent cleanser.

Where do we find them ?

Non irritating, amphoteres enter in the formulation of :

- numerous soft shampoos

- products for sensitive skin

- eye demak up

- dermatological toners and gels "

source : http://www.ac-bordeaux.fr/Etablissement/StLouis/OLYMP/cosmeto/cosmeto.pdf and translated by me