DMK4012
SURFACTANT CHEMISTRY
CHAPTER 2: SURFACTANTS
DEFINITION OF SURFACTANT
■ Surfactant is coming from the words surface active agents.
■ It is characterized by its tendency to adsorb at surfaces and interfaces.
■ It is an organic compound that widely used in detergent, cosmetics, pharmaceutical,
agriculture, biotechnology, etc.
■ Exist in natural and synthetic forms.
■ For a compound to be considered as a surfactant, it should possess the following
characteristics:-
1. Composed of polar and non-polar groups.
2. It should exhibit surface activity.
3. It should form self-assembled aggregates (micelles) in liquid.
SURFACTANT COMPOSITION AND STRUCTURES
■ Surfactant molecule consist of two structures:-
1. Polar head groups (hydrophilic, lipophobic or oleophobic)
2. Non-polar tail groups (hydrophobic, lipophilic or oleophilic)
■ The hydrophilic groups makes the surfactant soluble in polar solvent such as water. While,
the hydrophobic groups makes the surfactant soluble in non-polar solvent such as oil.
■ The relative sizes and shapes of the hydrophilic and hydrophobic parts of the surfactant
molecule determine many of its properties. Surfactant can have:-
1. One polar head and one non-polar tail
2. One polar head and two non-polar tail
3. Two polar head and one non-polar tail
4. Two polar head from two surfactant combined with rigid spacer (linear or ring organic
structure)
5. A number of surfactants (more than two) linked together with covalent bonds (polymeric
surfactant
ADSORPTION OF SURFACTANT
Cont...
■ Adsorption is the adhesion of atoms, ions, or
molecules from a gas, liquid or dissolved solid to a
interface.
■ There are two general types of adsorption:
1. Physical adsorption, in which the adsorbate is
bound to the surface or interface through the weak
van der waals forces or intermolecular forces.
2. Chemical adsorption or chemisorption, which
involves the stronger valences forces or
intramolecular forces (chemical bonding).
Cont...
Adsorbent – an adsorptive substance (atoms or
molecules at surface or interface)
Adsorbate – an adsorbed substance (surfactant
molecules)
The solid substance on the surface of which adsorption
occurs is known as adsorbent.
The substances that get adsorbed on the solid surface
due to intermolecular attraction are called adsorbate.
The adsorbent may be a solid or a liquid and the
adsorbate may be a gas or a solute in some solution.
CONT....
■ The adsorption of surfactant is divided into 3 categories,they are:-
1. Liquid-gas adsorption (foaming)
2. Liquid-liquid adsorption (emulsification)
3. Liquid-solid adsorption (dispersion, coating and detergency)
APPLICATION OF SURFACTANTS
■ Soap
■ Detergent
■ Lubricants
■ Pharmaceuticals
■ Cosmetics
■ Baked good
■ Margarine
■ Dairy-type emulsions
■ Salad dressings
CLASSIFICATION OF SURFACTANT
■ A simple classification based on the nature of the hydrophilic group on the surfactant
■ There are 4 types of surfactants, these classifications are based on upon the
composition of the polar head group. The classifcations as follow:-
1. Non-ionic surfactant
2. Anionic surfactant
3. Cationic surfactant
4. Amphoteric surfactant
Cont...
■ Non-ionic surfactant has no charge group in its head. Many long chain alcohols
exhibit some surfactant properties.
■ Anionic surfactant contain anionic functional group at their head, such as sulfonate,
phosphate, sulfate and carboxylates.
■ Cationic surfactant are comprised of a positibely charged head, such as quarternary
ammonium.
■ Amphoteric surfactant or zwitterion surfactants have both cationic and anionic
centers attached to the same molecule. The anionic part such as sulfonate and the
cationic part such as quarternary ammonium.
■ They are also biosurfactant that coming from natural resources.
■ Nowadays, researchers are studying on producing green surfactants either naturally
or synthetically which are biodegradables.
Anionic Surfactant
■ The most widely used class of surfactant in industrail application (50%).
■ Due to relatively low cost of manufacture and can be used in all type of detergent.
■ The optimum detergency for the hydrophobic chain is a linear alkyl group with a
chain length of 12-16 carbon.
■ Linear chains are preferred since they are more effective and more degradable than
branched chain.
■ The following examples are the most used anionic surfactants based on the polar
head:-
1. Carboxylates (R-COO-X)
2. Sulphates (R-OSO3- X)
3. Sulphonates (R-SO3-X)
4. Phosphates (R-OPO(OH)O-X)
■ The counter ion X is usually Na+
Carboxylates group
■ The earliest known surfactants since they constitute the earliest soaps
■ Eg. sodium or potassium stearate and sodium myristate
■ The alkyl group may contain unsaturated portion, eg. Sodium oleate, which contains
one double bond in the C17 alkyl chain.
■ Most commercial soaps are a mixture of fatty acids obtained from tallow, coconut
oil, palm oil, etc. The main attraction of these simple soaps is their low cost, their
ready biodegradability and low toxicity.
■ While the main disadvantage is they readily to form precipitation in water containing
bivalent ions such as Ca2+ and Mg2+ (hard water).
■ To avoid the precipitation the carboxylates are modified by introducing some
hydrophilic chains such as ethoxy carboxylates, ester carboxylate containg hydroxyl
or multi COOH groups.
■ The addition of these hydrophilic groups will increase water solubility and enhance
the chemical stability (no hydrolysis).
Sulphates group
■ These are the largest and most important class of synthetic surfactant.
■ Produced by the reaction of a fatty alcohol with sulphuric acid to form esters of
sulphuric acid.
■ In practice, the mixture of sulphur dioxide and air been used for sulphating the
alcohol.
■ The properties of sulphate surfactants depend on the nature of alkyl chain and the
sulphate group.
■ The most common suphate surfactant is sodium dodecyl sulphate (SDS) or also
known as sodium lauryl suphate (SLS).
■ At room temperature (25 ⁰C) or above SLS will be soluble but below room
temperature the surfactant will be separate out as a soft paste.
■ The critical micelle concentration of SLS is 8.0 x 10 -3 mol dm-3.
Sulphonates group
■ With suphonates, the sulfur atom is directly attached to the carbon atom of the alkyl
group, giving the molecules stability against hyrdolysis compared to sulphates.
■ Alkyl aryl sulphonates or linear alkyl benzene sulphonates (LABS) are the most
common type of these kind of surfactant.
■ Eg. Sodium alkyl benzene sulphonate
■ Usually prepared by reaction of sulfuric acid with alkyl aryl hydrocarbons (dodecyl
benzene)
Cont...
■ LABS are manufactured from alkyl benzene and the alkyl chain length can vary from
C8-C15, the most common is C10, sodium dodecyl benzene sulphonates.
■ The main disadvantages of LABS are their effect on the skin so it cannot be used in
personal care formulation.
■ Nowadays most of the detergent manufacturers are changing from LABS to methyl
ester sulphonates (MES) which are origin from palm oil.
■ MES is made from renewable natural resources which gives it excellent bio-
degradability, improved calcium hardness tolerance during the washing process and
superior detergency.
Nonionic surfactants
■ Nonionic surfactants come as a close second with about 45% of the overall
industrial production.
■ They do no ionize in aqueous solution because their hydrophilic head is neutral (no
charged) such as alcohol, phenol, acid, ester or amine.
■ Several classes can be distinguished as:-
1. Alcohol ethoxylates
2. Alkyl phenol ethoxylates
3. Fatty acid ethoxylates
4. Sorbitan ester and ethoxylated derivatives
5. Fatty amine ethoxylates
Alcohol ethoxylates
■ Produced by ethoxylation of a fatty alcohol such as dodecanol or lauryl alcohol
■ Several general names are given to this class of surfactants such as ethoxylated
fatty alcohols, alkyl polyoxyethylene glycol, monoalkyl poly(ethylene oxide) glycol
ethers.
■ A typical example is dodecyl hexaoxyethylene glycol mono ether (picture below).
Cont...
Alkyl phenol ethoxylates
■ These are prepared by reaction of ethylene oxide with alkyl phenol.
■ The most common example is nonylphenol ethoxylates.
■ These surfactants are cheap to produce but suffer from biodegradability and
potential toxicity .
■ Despite these problems, nonyl phenol ethoxylates are still be used because of their
solubility both in aqueous and non-aqueous media, good emulsification and
dispersion properties.
nonyl phenol ethoxylates
Fatty acid ethoxylates
■ These are produced by the reaction of ethylene oxide with a fatty acid
■ These surfactants are generally soluble in water provided there are enough EO units
and the alkyl chain length of the acid is not too long,
■ The surfactants are compatible with aqueous ions provided there is not much
unreacted acid. However, these surfactants undergo hydrolysis in highly alkaline
solutions.
■ The most common example are lauric acid ethoxylate and stearic acid ethoxylate
Sorbitan ester and their ethoxylated derivatives
■ Sorbitan ester of fatty acids (Spans, the commercial name) and their ethoxylated
derivatives (Tweens, the commercial name) are perhaps one of the most commonly used
nonionics surfactant.
■ The sorbitan ester are produced by reacting sorbitol with a fatty acid at a high
temperature ( > 200 ⁰C )
Sorbitol
Sorbitan tristearate
Cont...
■ The free OH group in the sorbitol can be esterified to produce mono, di- and tri-
esters.
■ Several products are available depending on the nature of the alkyl group of the acid
and whether the product is a mono-, di- or tri-ester. Some examples are:-
Sorbitan monolaurate (Span 20)
Sorbitan monopalmitate (Span 40)
Sorbitan monosterate (Span 60)
Sorbitan mono-oleate (Span 80)
Sorbitan tristearate (Span 65)
Sorbitan trioleate (Span 85)
Cont...
■ Ethoxylated derivatives are produced by the reaction of ethylene oxide on any
hydroxyl group remaining on the sorbitan ester group.
■ Some example of Tween surfactants are given below:-
1. Polyoxyethylene (20) sorbitan monolaurate (Tween 20)
2. Polyoxyethylene (20) sorbitan monopalmitate (Tween 40)
3. Polyoxyethylene (20) sorbitan monostearate (Tween 60)
4. Polyoxyethylene (20) sorbitan tristearate (Tween 65)
5. Polyoxyethylene (20) sorbitan trioleate (Tween 85)
■ Sorbitan esters and their ethoxylated derivatives has been approved as food
additives
■ They are widely used in cosmetics and pharmaceutical products.
Fatty amine ethoxylates
■ Prepared by the addition of ethylene oxide to primary or secondary fatty amines.
■ With primary amines both hydrogen atoms on the amine group react with ethylene
oxide while for secondary amine only one hydorgen atom react with ethylene oxide.
■ The fatty amine ethoxylates are used as emulsifiers and can also be employed in
formulation of emulsifier blends.
■ They play an important role as emulsifiers in agrochemical industries, cleaners in
industrial processes especially in metal industry, oil field chemicals, fabric softeners,
petroleum additives and for applications in textile and leather processing, paper de-
inking, mining & drilling.
Cationic Surfactant
■ Cationic surfactant is a class of surfactant that containing positive charged at the
hydrophilic head.
■ The most common cationic surfactants are containing the quarternary ammonium
compound with chloride ion as the anion or counter ion.
Cont...
■ A common class of cationic surfactants is the alkyl trimethyl ammonium chloride,
with the alkyl group having a chain length of 8-18 C atoms, Eg. dodecyl trimethyl
ammonium.
■ Another widely used cationic surfactant class is that containing two long-chain alkyl
groups, ie. dialkyl dimethyl ammonium chloride, with the alkyl groups having a chain
length of 8-18 C atoms.
Didecyl dimethyl ammonium chloride
■ These type of surfactants are commonly used in detergents as fabric softeners.
Cont..
■ Another form of quarternary ammonium surfactant is imidazolines. Eg. below
Ditallow derivative quaternized with dimethyl sulphate
■ Cationic surfactants are generally water soluble when there is only one alkyl group.
■ They are generally compatible with most inorganic ions and hard water
■ They generally stable to pH changes, both acid and alkaline.
■ The prime use of cationic surfactants is their tendency to adsorb at negatively
charged surfaces
Amphoteric Surfactants
■ Containing both cationic and anionic group
■ Also known as zwitterionic surfactants
■ In most cases it is the pH which determines which group would dominate, by
favoring one or the other ionization: anionic at alkaline pH and cationic at acid pH.
Near the isoelectric point.
■ The most common amphoterics are the N-alkyl betaines, which are the derivatives of
trimethyl glycine or betaine.
■ Eg. Lauryl amido propyl dimethyl betaine/cocamidopropyl betaine
betaine
cocamidopropyl betaine
Cont..
■ The main characteristic is their dependence on the pH of the solution in which they
are dissolved.
■ In acid solution, the molecule acquires a positive charge and behave like a cationic
surfactant.
■ In alkaline solution, they become negatively charged and behave like an anionic
one.
■ A specific pH can be defined at which both ionic groups show equal ionization (the
isoelectric point)
Cont..
■ The change in charge with pH of amphoteric surfactants affects their properties,
such as wetting, detergency, foaming etc.
■ At the isoelectric point, the amphoteric surfactants resemble those of non-ionics
■ Below and above the isoelectric point the properties shift towards those of cationic
and anionic surfactants.
■ Zwitterionic surfactants have excellent dermatological properties
■ They also exhibit low eye irritation and are frequently used in shampoos and the
other personal care products.
Biosurfactants
■ Biosurfactants are amphiphilic compound produced in living surfaces, mostly on
microbial cell surfaces or excreted extracellular hydrophobic and hydrophilic
moieties.
■ They possess the characteristics property of reducing the surface and interfacial
tension using the same mechanisms as chemical surfactants
■ Biosurfactants are mainly classified according to their chemical structure and their
microbial origin
■ The main classes of biosurfactants are:-
1. Glycolipid
2. Phospholipid
3. Polymeric biosurfactant
4. Lipopeptides (surfactin)
