1.Emulsifying agents help the production of a stable emulsion
3.If a substance is added which alters the solubility of the emulsifying agent, this balance may be altered and the emulsion may change type
4.An ideal emulsifying agent should be
Naturally Occurring Emulsifying Agents
1. Polysaccharides
•
Acacia is the best emulsifying agent as it forms a thick
film at the oil-water interface to act as a barrier to
coalescence
2.
Semisynthetic polysaccharides
•
Low-viscosity grades of methylcellulose and
carboxymethyl-cellulose are used to form o/w
emulsions
3.
Sterol-containing substances
•
These agents act as water-in-oil emulsifying agents.
Examples include beeswax, wool fat and wool alcohols
Synthetic Surfactants
1.
Anionic surfactants
a)
These are organic salts which, in water, have a surface-active
anion.
b)
They are widely used in external preparations as o/w
emulsifying agents
c)
They must be in their ionized form to be effective
d)
Emulsions made with anionic surfactants are generally
stable at more alkaline pH
e)
They are incompatible with some organic and inorganic
cations (e.g. cetrimide)
c)
Examples are sodium stearate, calcium oleate,
triethanolamine oleate, sodium lauryl sulphate
COO
-
Synthetic Surfactants (Con’t)
2.
Cationic surfactants
a)
These are usually quaternary ammonium
compounds which have a surface-active cation
b)
They are used in the preparation of o/w emulsions
for external use
c)
Emulsions formed by a cationic surfactant are
generally stable at acidic pH
d)
Incompatible with
anionic surfactants and drugs
d)
They usually have antimicrobial activity
e)
Examples are cetrimide and benzalkonium chloride
N
+
Synthetic Surfactants (Con’t)
3.
Non-ionic surfactants
a)
They are used to produce either o/w or w/o emulsions
for both external and internal use
b)
They are highly resistant to pH change
c)
The non-ionic surfactants are compatible with both
anionic and cationic substances
c)
The type of emulsion formed depends on the balance
between hydrophilic and lipophilic groups which is
given by the HLB (hydrophilic-lipophilic balance)
number
d)
Examples are glycerol esters, sorbitan esters and
polysorbates
The HLB (hydrophilic-lipophilic
balance) system
a)
An HLB number represents the relative proportions
of the lipophilic and hydrophilic parts of the
emulsifying agent
b)
High numbers (8-18) indicate a hydrophilic molecule,
and produce an o/w emulsion
c)
Low numbers (3-6) indicate a lipophilic molecule and
produce a w/o emulsion
Emulsifying agent
HLB value
Glyceryl monosterate
3.8
Sorbitan monosterate
4.7
Polysorbate 20
16.7
