Surfactants

1
Surfactants and Its Importance
 Surfactants (Surface Active Agents)

Surfactants are materials that

lowers the surface tension (or
interfacial tension) between two
liquids or between a liquid and a
solid.

Also can be termed as

Amphiphiles as it contains both
hydrophilic and hydrophobic
regions.
 Structure of Surfactant

⚫ Surfactant have Amphipathic Structure.

Head
Tail

Tail or Hydrophobic Group-

Little affinity for bulk solvent. Usually hydrocarbon chain
in aqueous solvent, can be linear or branched.

Head or hydrophilic Group.- is usually a polar group like

carboxylic, sulphate, or sulphonate group.
Strong Affinity for bulk solvent, can be neutral or charged.
 Sodium dodecyl sulphate .The polar "head" has affinity for water and the "tail" has
affinity for oil
 Classification of surfactants
Surfactant can be classified based on charge groups present in their head. A nonionic
surfactant do not have any charge groups over its head. The head of an ionic surfactant
carries a net charge. If the charge is negative, the surfactant is more specifically called
anionic and if the charge is positive, it is called cationic.
If a surfactant contains a head with two oppositely charged groups, it is termed
zwitterion.

1. Anionic surfactants
2. Cationic surfactants
3. Non-ionic surfactants
4. Zwitterionic/ amphoteric surfactants
 Classification of Surfactants

⚫ A non-ionic surfactant has no charged groups in its head.

Non Ionic

Anionic

Cationic

zwitterionic
 1.) Non Ionic Surfactants

⚫ Nonionic surfactants have covalently bonded oxygen-containing

hydrophilic groups, which are bonded to hydrophobic parent
structures.
⚫ Water Soluble.
⚫ Solubility decreases with increase in temperature.
 Nonionic surfactants

 Those surfactants do not have any electrical charge, which makes them
resistant to water hardness deactivation.
 They are less irritant than other anionic or cationic surfactants.
 The hydrophilic part contains the polyoxyethylene, polyoxypropylene or
polyol derivatives.
 The hydrophobic part contains saturated or unsaturated fatty acids or fatty
alcohols
They are excellent grease/oil removers and emulsifiers.
Advantages of Nonionic type surfactants :
 As a class they are usually the least irritating

 They are compatible with all the other type

surfactants.

 They are compatible with salts

 They are compatible at the widest pH range

 They are pre-formed

 As a class they are the most versatile

 The non ionic surfactant can be classified as

• Polyol esters ,
• polyoxyethylene esters ,
• poloxamers .
 The Polyol esters includes glycol and glycerol esters and sorbitan
derivatives.
 Polyoxyethylene esters includes polyethylene glycol (PEG 40,PEG -50,
PEG- 55).
 The most commonly used non-ionic surfactants are ethers of fatty
Alcohols.
Examples of Non Ionic Surfactants
 Anionic surfactants:

In solution, the head is negatively charged.

These surfactants are the most widely used type
of surfactant for preparing shampoos because
of its excellent cleaning properties and high hair
conditioning effects. Anionic surfactants are
particularly effective at oil cleaning and oil/clay
suspension.
Anionic surfactants contain anionic functional
groups at their head, such as sulfate, sulfonate,
phosphate and carboxylate.
The most commonly used anionic surfactants are alkyl sulphates, alkyl ethoxylate
sulphates and soaps. Most of the anionic surfactants are carboxylate ,sulfate and
sulfonate ions .(ARG Remington ,The science and practice of pharmacy ,19th edn ,Vol 1) . The straight chain is a
saturated /unsaturated C12-C18 aliphatic group. The water solubility potential of
the surfactant is determined by the presence of double bonds . (G.Zagrafti .The science and practice
of pharmacy)
 Anionic Surfactants
1.) Suphate, Sulphonate and Phosphate Esters :-
⚫ Prominent sulfates includes

o Salts of higher fatty acids (soaps)

Sodium dodecyl sulfate (SDS)
(Sodium lauryl sulphate (SLS)) (widely used to produce o/w emulsions).

Sodium glycocholate,
Sodium taurocholate
o Alkylbenzene sulfonates (detergents)
Sodium Oleate: CH3(CH2)7CH=CH(CH2)7COO -
Na+

Sodium Dodecyl sulphate(SDS)

Sodium Dodecyl benzene sulphonate: CH3(CH2)11C6H4SO3- Na+

Sodium Stearate: CH3(CH2)16COO- Na+

 Docusate (dioctyl sodium sulfosuccinate)
⚫ Perfluoro octane suphonate (PFOS)

⚫ Perfluoro butane suphonate

I. ORGANO PHOSPHORED SURFACTANTS

e.g., : Potasium Laureth Phospate (Dermalcare 213L/K)
II. SARCOSIDES OR ALCYL AMINO ACIDS
e.g., : Sodium lauroil sarcosinate (Crodasinic LS 30), Cocamide DEA, Cocamide MEA
The most used synthetic product is lauryl sarcosinate, which is both a strong
bactericide and a blocking agent of hexokinase (putrefaction enzyme). Since it is not
cationic, it is compatible with anionic surfactants, and it is used in tooth paste and
"dry" shampoos for carpets and upholstery.
⚫ Alkyl-aryl ether phosphates

⚫Alkyl ether phosphates

⚫2.) Carboxylates

These are the most common surfactants and comprise the

carboxylate salts (soaps), such as Sodium Sterate. More
specialized species include Sodium Lauroyl Sarcosinate and
carboxylate-based fluorosurfactants such as Perfluorononanoate,
Perfluorooctanoate (PFOA or PFO).
 Cationic surfactants
In solution, the head of the cationic surfactant is positively charged.(Polar Head is
Positively Charged)
Cationic surfactants are quaternary ammonium compounds and they are mostly
used for their disinfectant and preservative properties as they have good
bactericidal properties. They are used on skin for cleansing wounds or burns.
Mostly used cationic surfactants are cetrimide which has tetradecyl trimethyl
ammonium bromide with minimum amount of dodecyl and hexadecyl compounds
. Other cationic surfactants are benzalkonium chloride, cetylpyridinium chloride
etc.
1. QUATERNARY COMPOUNDS or QUATS.
They are not good detergents nor foaming agents, and they cannot be mixed in
formulations which contain anionic surfactants, with the exception of non
quaternary nitrogenated compounds, or when a catanionic complex synergetic
action is sought.

Quaternary compound (quats) Benzalkonium Chloride

The quats kill bacterial spores but rather than inhibit their growth. They form a residual

antimicrobial film after being applied to surfaces. They attached to the bacteria and

cause the cytoplasmic membrane to leak, damaging and kill the bacteria. The quats are

low in toxicity, non irritant to skin and can be neutralized or made ineffective by using

any anionic detergent.

Quat sanitizers are generally more effective in the alkaline pH range. However the effect

of pH may vary with bacterial species, with gram-negative bacteria being more

susceptible to quats in the acid pH range and gram-positive microbes in the alkaline

range.
Quats inactivated by anionic detergents (soaps), by many nonionic detergents, and by

calcium, magnesium, ferric, and aluminum ions. Also, they are not recommended to be

used in hard water. Effective levels are at 200 ppm. However, an increase in alkalinity

through formulation with compatible detergents may enhance the bactericidal activity

of the quats
2. OTHER CATIONIC SURFACTANT

Cationic class contains aromatic or saturated heterocycles is N-dodecyl pyridinium chloride

or 1-hexadecyl Pyridium Chloride (INCI: Cetyl Pyridium Chloride) is used as batericide and

fungicide. If a second hydrophilic group is added (amide, ethylene oxide) the product is the

both a detergent and a bactericide. is compatible with anionic formulas since it is not

strictly cationic.

They also found as antistatic agents in fabric softeners and hair rinse formulas. E.g., Ester

quats-sunqat TE 90 (softening agent), CTAC or BTAC as anti static agent

3. NITROGENATED SURFACTANTS WITH A SECOND HYDROPHILE
Cationic surfactants cannot be mixed in general with anionics, since they react

with one another to produce insoluble catanionic compounds. This is quite a

practical problem since most inexpensive formulas contain anionics of the

sulfonate or sulfate ester type, and it would be desirable to add to them some

cationic substance for softening purpose.

The incompatibility problem is circumvented by using a nitrogenated

surfactant of the amine type, i.e. with no actual positive ion, whose water

solubility is enhanced by incorporating a second polar group.

1. ALKANOL-AMIDES

They are among the best foam boosters available at neutral and alkaline

pH, with additional corrosion inhibition properties at neutral pH.

Fatty acid alkanol-amides are commonly used as foaming and wetting

agents in hand dish-washing detergents, shampoos and bar soaps,

particularly the diethanol- lauryl (coco) amide. E.g., : Cocamide DEA,

cocamide MEA
 Cationic Surfactants

Examples :-

1.) pH-dependent primary, secondary,

or tertiary amines.

2.) Permanently charged quaternary

ammonium salts :
Cetrimonium Bromide (CTAB)
Cetylpyridinium chloride (CPC)
Benzalkonium chloride (BAC)
Benzethonium chloride (BZT)
Dimethyldioctadecylammonium
chloride
Dioctadecyldimethylammonium
bromide (DODAB)
 Amphoteric surfactants
Amphoteric or zwitterionic surfactants have two functional group, one anionic

and one cationic. In most cases it is the pH which determines which of the

groups would dominate. with a minimum of interfacial activity and a

concomitant maximum of water solubility.

Amphoteric surfactants, particularly the aminoacid ones are quite

biocompatible, and are used in pharmaceuticals and cosmetics.

 These surfactants are very mild, making them particularly suited for use in
personal care preparations over sensitive skins.
 They can be anionic (negatively charged), cationic (positively charged) or
non-ionic (no charge) in solution, depending on the acidity or pH of the
water.
 Those surfactants may contain two charged groups of different sign.
Whereas the positive charge is almost always ammonium but the source of the
negative charge may vary (carboxylate, sulphate, sulphonate).
 These surfactants have excellent dermatological properties. They are
frequently used in shampoos and other cosmetic products, and also in hand
dishwashing liquids because of their high foaming properties.

(Zhang W, Dai X et al)

1. AMINO PROPIONIC ACIDS
The general formula for amino propionic acids is RN+-CH2-CH2-COO- . Their

isoelectric point is around pH = 4. They are soluble in acid or alkaline

solutions. They adsorb on skin, hair, and textile fibers. They are used as

antistatic and lubricants for hair and fabrics. The dodecyl amino propionic

acid is used in cosmetics as wetting agent and bactericide. At high pH it is

good detergent and foaming agent. However, due to their carboxylic acid

groups, these surfactants are sensitive to divalent cations.

2. IMIDO PROPIONIC ACIDS

Their general formula is HOOC-CH2-CH2-RN+H-CH2-CH2-COO-. Their

isoelectric point is around pH = 2-3. They are thus more water soluble

than the previous ones. They are used as textile softeners. Dicarboxylic

compounds of alkyl imidazole, in which the alkyl group is located on the

carbon placed between the nitrogen atoms, are used in cosmetics and

de luxe soap bars.

QUATERNIZED COMPOUNDS
Quaternized compound have similar structures. The most important are
betaines and sulfobetaines or taurines, which have a single methylene group
between the acid and the quaternary ammomium.

These surfactants are amphoteric at neutral and alkaline pH, and cationic at
acid pH (at which the carboxylic acid is not ionized). Since the nitrogen atom is
quaternized, these surfactants always display a positive charge. They tolerate a
high salinity, particularly divalent cations, e.g. calcium and magnesium.
 They are the most used class of amphoteric surfactants. They are found in

softeners for textiles, hair rinse formulas, and corrosion inhibition additives.

They are good foam boosters because of their cationic characteristics.

Sulfobetaines have an anionic group (sulfonate) which tolerates calcium ions,

and are used as lime soap dispersing agents (LSDA) in de luxe soap bars and

detergents.
 HLB Scale

It is the measure of the degree to which the molecule is hydrophilic or lipophilic

The HLB value can be used to predict the

surfactant properties of a molecule:

< 10 : Lipid-soluble (water-insoluble)

> 10 : Water-soluble (lipid-insoluble)
1 to 3: anti-foaming agent
3 to 6: W/O (water in oil) emulsifier
7 to 9: wetting and spreading agent
13 to 16: detergent
8 to 16: O/W (oil in water) emulsifier
16 to 18: solubiliser or hydrotrope
 Importance of Surfactants
⚫ QUATs as Anti Microbials

Quaternary ammonium compounds have also been shown to have antimicrobial activity.
Certain quaternary ammonium compounds, especially those containing long alkyl
chains, are used as antimicrobials and disinfectants.
Kills the Germs by Disrupting Cell Membranes.
Examples benzalkonium chloride, benzethonium chloride,
methylbenzethonium chloride, cetalkonium chloride etc.
⚫ As a Wetting Agent

A surfactant that, when dissolved in water, lowers the advancing contact angle, aids in
displacing an air phase at the surface, and replaces it with a liquid phase

Eg. 1.) the displacement of air from the surface of sulfur, charcoal, and other powders for
the purpose of dispersing these drugs in liquid vehicles
2.) the displacement of dirt and debris by the use of detergents in the washing of wounds;
and the application of medicinal lotions and sprays to surface of skin and mucous
membranes. The cleaning action of soaps and detergents is termed as detergency

⚫ Detergency
The cleaning action of soaps and detergents is termed as detergency.

It is most important property of surface active agents. Surface active agents are referred
as detergents. The term Detergency is mostly used in the cleaning / removing of grease,
oil and dirt from the solid surface. The principle of detergency is based on the formation of
micelle.

The process needs many of the actions specific to surfactant molecules.

1.The surfactant requires good wetting properties to ensure good contact with the solid
surface.
1. It also has the ability to remove dirt into the bulk liquid.

 This property is achieved by lowering the surface tension of the medium in

which surfactants is dissolved.
 By lowering this interfacial tension between two media or interfaces (e.g.
air/water, water/stain, stain/fabric) the surfactant plays a key role in the removal
and suspension of dirt.
 The lower surface tension of the water makes it easier to lift dirt and grease off of
dirty dishes, clothes and other surfaces, and help to keep them suspended in the
dirty water.

 The water-loving or hydrophilic head remains in the water and it pulls the
stains towards the water, away from the fabric.
 The surfactant molecules surround the stain particles, break them up and force them
away from the surface of the fabric.
 They then suspend the stain particles in the wash water to remove them. If the dirt
is oily it may be emulsified or solubilized by the surfactant.
⚫ Lung/Pulmonary Surfactant

Pulmonary surfactant is a mixture of lipids and proteins which is secreted by the epithelial
type II cells into the alveolar space. Its main function is to reduce the surface tension at the
air/liquid interface in the Lung and keep them from collapsing when an individual
exhales.

One of the most important pharmaceutical pulmonary surfactants is Survanta (beractant)

⚫ As an Emulsifier
A Substance which Stabilizes a Emulsion.
Eg . Acacia , Polysorbate 20, 40, 60, 80, Lecithin etc.
 This is the property of surfactants to form a stable emulsion of two or more
immiscible liquids.
 When oil and water mixed together and agitated, droplets of varying size are
produced.
 Tension exists at the interface because the two immiscible liquid phases
tend to have different attractive forces for a molecule at the interface.

 Molecules of one phase are repelled by other phase due to greater interfacial
tension, but for dispersion of liquid necessary of reduction of interfacial
tension.
This is done by addition of surfactants and having following mechanisms.

• Reduction of interfacial tension – Thermodynamic stabilization.

• Formation of interfacial film – mechanical barrier to coalescence.
•Formation of electrical double layer – electrical barrier to approach of
particles.
⚫ Foaming and Antifoaming Agents.

Foaming is useful in case of antimicrobial formulation and also in Cosmetics such

as Shaving Creams, Face wash, Shampoo, Conditioners etc.
Anti Foaming Agents include Alcohol , Ether , Castor Oil used to break the Foam.
⚫ Bio-Surfactants

Defined as the surface-active biomolecules produced by microorganisms with

wide-range of applications.

Increasing mobility, increasing solubility, lubrication, wetting, rewetting,

softening, fixing dyes, making emulsions, stabilizing dispersions, coagulating
suspended solids, making foams, preventing foam formation and defoaming.

The most significant application of biosurfactants was studied in

bioremediation for example in removing heavy metals from soils.
 Solubilization
• Solubilization can be defined as ‘‘the preparation of a thermodynamically stable
isotropic solution of a substance normally insoluble or very slightly soluble in a
given solvent by the introduction of an additional amphiphilic component or
components.

• ’’ The amphiphilic components (surfactants) must be introduced at a

concentration at or above their critical micelle concentrations.
• Simple micellar systems (and reverse micellar) as well as liquid crystalline
phases and vesicles referred to above are all capable of solubilization.

• In liquid crystalline phases and vesicles, a ternary system is formed on

incorporation of the solubilizate and thus these anisotropic systems are not
strictly in accordance with the definition given above.
 Other Applications

⚫ Paints
⚫ Ink
⚫ Toothpaste
⚫ Hair Conditioners
⚫ Sanitizers
 References

1.) Martins, Physical Pharmacy and Pharmaceutical Science

,Sixth Edition, Lipincott Williams & Wilkins, 2011, Pg no
355-382
2.)M.E Alton, The Science of Dosage From Design, Second
Edition, Churchill Livingstone, Pg no. 54-69
3.) Wikipedia- The free Encyclopedia.