CHEE2945 – Lecture 4
Surfactants:
- Surfactants are comprised of a hydrophobic and a hydrophilic component.
- They are also known as amphiphiles, or amphiphilic molecules.
- The relative properties of the hydrophobic and hydrophilic sections determine
the surfactant behaviour, e.g., if it will stabilise oil in water (o/w) or water in oil
(w/o) emulsions.
- They are pictured as having a head and a tail.
- Most commonly, surfactants have a hydrophilic head and hydrophobic tail.
- Tails are usually long hydrocarbon (or sometimes fluorocarbon) groups.
- They can be either cationic (positive charged head), anionic (negatively
charged head) or non-ionic (neutral head).
- The head group has:
o Strong affinity for water,
o Weak affinity for air or oil,
o Absorbs readily at mineral oxide/water interfaces.
- The tail group has:
o Weak affinity for water,
o Strong affinity for oil and air,
o Absorbs at hydrophobic surfaces (e.g., graphite).
Cationic surfactants:
- Approximately 10% of industrial surfactants are cationic.
- Many cationic surfactants are amines. For example, cetyl trimethyl ammonium
bromide C16H33N(CH3)3+ Br- (CTAB). This compound is very important in
research as it is usually very pure.
Anionic surfactants:
- Approximately 60% of industrial applications are anionic.
- They are often sulphates. One example is sodium dodecyl sulphate C 12H27-
SO4- Na+ (SDS). It is commonly used in shampoos and detergents. Another
common example is sodium laureth sulphate (SLES), which is an ethoxylated
version of SDS. It is milder on skin and cheap.
- They are also often sulphonates, e.g., sodium dodecyl sulphonate. These are
common in consumer care products.
Surfactants:
- Surfactants are comprised of a hydrophobic and a hydrophilic component.
- They are also known as amphiphiles, or amphiphilic molecules.
- The relative properties of the hydrophobic and hydrophilic sections determine
the surfactant behaviour, e.g., if it will stabilise oil in water (o/w) or water in oil
(w/o) emulsions.
- They are pictured as having a head and a tail.
- Most commonly, surfactants have a hydrophilic head and hydrophobic tail.
- Tails are usually long hydrocarbon (or sometimes fluorocarbon) groups.
- They can be either cationic (positive charged head), anionic (negatively
charged head) or non-ionic (neutral head).
- The head group has:
o Strong affinity for water,
o Weak affinity for air or oil,
o Absorbs readily at mineral oxide/water interfaces.
- The tail group has:
o Weak affinity for water,
o Strong affinity for oil and air,
o Absorbs at hydrophobic surfaces (e.g., graphite).
Cationic surfactants:
- Approximately 10% of industrial surfactants are cationic.
- Many cationic surfactants are amines. For example, cetyl trimethyl ammonium
bromide C16H33N(CH3)3+ Br- (CTAB). This compound is very important in
research as it is usually very pure.
Anionic surfactants:
- Approximately 60% of industrial applications are anionic.
- They are often sulphates. One example is sodium dodecyl sulphate C 12H27-
SO4- Na+ (SDS). It is commonly used in shampoos and detergents. Another
common example is sodium laureth sulphate (SLES), which is an ethoxylated
version of SDS. It is milder on skin and cheap.
- They are also often sulphonates, e.g., sodium dodecyl sulphonate. These are
common in consumer care products.
