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SURFACTANTS IN SOLUTION. Amphiphilic Surfactants. Amphiphilic surfactants contain a non-polar portion and a polar portion . . Aerosol OT. Classification of Surfactants. Anionic Cationic Zwitterionic Nonionic. Sodium dodecylsulfate (SDS). Cetylpyridinium bromide.

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amphiphilic surfactants
Amphiphilic Surfactants

Amphiphilic surfactants contain a non-polar portion anda polar portion.

Aerosol OT

classification of surfactants
Classification of Surfactants
  • Anionic
  • Cationic
  • Zwitterionic
  • Nonionic

Sodium dodecylsulfate (SDS)

Cetylpyridinium bromide

Dipalmitoylphosphatidylcholine (lecithin)

Polyoxyethylene(4) lauryl ether (Brij 30)

surfactant aggregates

4 nm

Surfactant Aggregates

Normal micelles

Unimers

cylindrical

spherical

Inverted hexagonal phase

Reverse micelles

Bilayer lamella

molecular architecture
Molecular Architecture

Aerosol OT

Sodium dodecylsulfate (SDS)

slide6

14

12

10

8

CMC

6

4

2

0

0

Surfactant concentration

1

Critical Micelle Concentration

CMC

Below CMC only unimers are present

Above CMC there are micelles in equilibrium with unimers

slide7

14

Concentration

unimers

14

Osmotic pressure

12

12

10

10

8

8

CMC

6

CMC

6

micelles

4

4

2

2

0

0

0

1

Surfactant concentration

0

1

Surfactant concentration

14

14

1/R

Molar conductivity

Isc

12

12

Light scattering

10

10

8

8

CMC

CMC

6

6

4

4

2

2

0

0

0

1

0

1

(Surfactant concentration)1/2

Surfactant concentration

Solution Properties

solubilization

Reverse micelles

Normal micelles

polar compound

non-polar compound

Solubilization

Spontaneous transfer of a compound insoluble in the bulk solvent into solution due to incorporation into the surfactant micelles

amphiphilic compound

solubility effects

14

Solubility

12

10

8

CMC

6

4

2

0

0

Surfactant concentration

1

Solubility Effects

Solubility of a poorly soluble compound increases as a result of solubilization in the micelles

hlb and use of surfactants
HLB and Use of Surfactants

Amphiphilic surfactants are characterized by the hydrophilic-lipophilic balance (HLB): a relative ratio of polar and non-polar groups in the surfactant

HLB ca. 1 to 3.5: Antifoams

HLB ca. 3.5 to 8: Water-in-Oil Emulsifiers

HLB ca. 7 to 9: Wetting and spreading agents

HLB ca. 8 to 16: Oil-in-Water Emulsifiers

HLB ca. 13 to 16: Detergents

HLB ca. 15 to 40: Solubilizers

required hlb
Required HLB

HLB needed for emulsification of the oil phase. If there are several oil ingredients the required HLB is calculated as a sum of their respective required HLB multiplied by the fraction of each.

  • Calculate the required HLB for the oil phase of the following o/w emulsion: cetyl alcohol 15 g., white wax 1g. Lanolin 2 g, emulsifier (q.s.), glycerin 5 g. water 100 g.
    • Required HLB Fraction
    • (from reference)
    • Cetyl alcohol 15 x 15/18 12.5
    • White wax 12 x 1/18 0.7
    • Lanolin 10 x 2/18 1.1
    • Total required HLB 14.3
hlb of surfactant blend
HLB of Surfactant Blend

Surfactant blends are commonly used to obtain desired emulsifying properties.

  • What is the HLB of the mixture of 40 % Span 60 (HLB = 4.7) and 60 % Tween 60 (HLB = 14.9)?
    • HLB of mixture:
      • 4.7 x 0.4 + 14.9 x 0.6 = 10.8
  • In what proportion should Span 80 (HLB = 4.3) and Tween 80 (HLB = 15.0) be mixed to obtain “required” HLB of 12.0?
    • 4.3.(1-x) + 15.x = 12 x = 0.72
    • 72 % Tween 80 and 28 % Span 80