Molecules and ions that are absorbed at the interface
is termed as Surfactants
Surfactants have two distinct regions in their chemical
structure, one of which is water-liking or Hydrophilic
and the other of which is water-hating or
These molecules are referred to as Amphiphilic or
Amphipathic molecules or simply as Surfactants or
Surface active agents.
The functional groups such as alcoholic (-OH),
carboxylic acid (-COOH), sulphate (-SO4) & quaternary
ammonium(NH4+) contribute to hydrophilic portion
Alkyl chains contribute to lipophilic nature of
The polar end oriented towards the water as well as the
non polar end projected upwards to space.
• When a surfactant is placed in water it forms micelles at
concentrations above its critical micelle concentration(CMC),
they form aggregates known as micelles.
• In a micelle, the hydrophobic tails flock to the interior in
order to minimize their contact with water, and the hydrophilic
heads remain on the outer surface in order to maximize their
contact with water .
• Critical micellar concentration is the concentration at which
the monomeric surfactant molecules associates into small
aggregates called micelles.
• Diluting the surfactant solution to below the cmc causes the
micelles to disperse or break up into single or non associated
• Micelles are not static aggregates but dissociate, regroup and
• There is a dynamic equilibrium between single surfactant
molecules and micelles.
• The shape of micelles in dilute surfactant solutions
is approximately spherical.
•Solubilization can be defined as the spontaneous dissolving of
a substance by reversible interaction with the micelles of a
surfactant in water to form a thermodynamically stable isotropic
solution with reduced thermodynamic activity
•At surfactant concentrations above the cmc the solubility
increases linearly with the concentration of surfactant,
indicating that solubilization is related to micellization.
•The lower is the CMC value and higher the aggregation
number , the more stable are the micelles.
• Sodium Lauryl Sulphate BP
• Mixture of sodium alkyl sulphates, the chief of which is
sodium dodecyl sulfate, C12 H25 SO4 – Na+
• It is very soluble in water at room temperature, and is used
• pharmaceutically as a preoperative skin cleaner, having
• Bacteriostatic action against gram-positive bacteria, and
also in medicated shampoos
• Component of emulsifying wax.
cationic surfactants are important pharmaceutically
because of their bactericidal activity against a wide range
of gram-positive and some gram-negative organisms.
• They may be used on the skin, especially in the cleaning of
• Their aqueous solutions are used for cleaning
• These are not ionised in aqueous solution
• Polyoxy ethylene sorbitan fatty acid esters
• Sorbitan esters are supplied commercially as Spans and
are mixtures of the partial esters of sorbitol and its monoand di-anhydrides with oleic acid.
• They are generally insoluble in water (low hydrophile –
lipophile balance (HLB) value) are used as water-in-oil
emulsifiers and as wetting agents.
• Polysorbates are complex mixtures of partial esters of sorbitol
and its mono and di-anhydrides condensed with an
approximate number of moles of ethyleneoxide.
• They are supplied commercially as Tweens. The polysorbates
are miscible with water, as reflected in their higher HLB
values, and are used as emulsifying agents for oil-in-water
They are added to the drugs in order to increase the product
characteristics in the design of dosage forms in a variety of ways like
solublising agents, wetting agents ,detergents, suspending ,foaming,
INFLUENCES THE DRUG ACTION
These are at low conc. Enhances the penetration of hexylresorcinol
into pinworm ,ascaris.
These are alter the integrity and lost the essential elements by leak
Mainly cationic surfactants show activity
But non ionic surfacants help in metabolism of organisms & facilitate their
• Natural surfactants enhances the absorption of antibiotics
They can be used in shampoos & lathering shaving cream so it can
produce stable foam when mixed with air pockets enclosed with thin film
ANTI FOAMING AGENTS
They can be used in fermentation process to prevents the foams in
production .eg., octnol, ether, castor oil & silicones
SOME ARE DRUGS
Phenothiazine & procaine-tranquilizer, local anesthetic
Veratrum alkaloids-anti cancer
M. J. Rosen. Surfactants and
Interfacial Phenomena (3rd
edn.), John Wiley
R. Zana (ed.). Dynamics of
Surfactant Self-Assemblies, CRC
3. M. Abe & J. F. Scamehorn.
Mixed Surfactant Systems, CRC